![Cong Wang](/assets/img/avatar_default.png)
cec_timer_fn() is a timer callback which reads ce_arr.array[] and
updates its decay values. However, it runs in interrupt context and the
mutex protection the CEC uses for that array, is inadequate. Convert the
used timer to a workqueue to keep the tasks the CEC performs preemptible
and thus low-prio.
[ bp: Rewrite commit message.
s/timer/decay/gi to make it agnostic as to what facility is used. ]
Fixes: 011d826111
("RAS: Add a Corrected Errors Collector")
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tony Luck <tony.luck@intel.com>
Cc: linux-edac <linux-edac@vger.kernel.org>
Cc: <stable@vger.kernel.org>
Link: https://lkml.kernel.org/r/20190416213351.28999-2-xiyou.wangcong@gmail.com
536 lines
12 KiB
C
536 lines
12 KiB
C
// SPDX-License-Identifier: GPL-2.0
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#include <linux/mm.h>
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#include <linux/gfp.h>
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#include <linux/kernel.h>
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#include <linux/workqueue.h>
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#include <asm/mce.h>
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#include "debugfs.h"
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/*
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* RAS Correctable Errors Collector
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*
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* This is a simple gadget which collects correctable errors and counts their
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* occurrence per physical page address.
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*
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* We've opted for possibly the simplest data structure to collect those - an
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* array of the size of a memory page. It stores 512 u64's with the following
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* structure:
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*
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* [63 ... PFN ... 12 | 11 ... generation ... 10 | 9 ... count ... 0]
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*
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* The generation in the two highest order bits is two bits which are set to 11b
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* on every insertion. During the course of each entry's existence, the
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* generation field gets decremented during spring cleaning to 10b, then 01b and
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* then 00b.
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*
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* This way we're employing the natural numeric ordering to make sure that newly
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* inserted/touched elements have higher 12-bit counts (which we've manufactured)
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* and thus iterating over the array initially won't kick out those elements
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* which were inserted last.
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*
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* Spring cleaning is what we do when we reach a certain number CLEAN_ELEMS of
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* elements entered into the array, during which, we're decaying all elements.
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* If, after decay, an element gets inserted again, its generation is set to 11b
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* to make sure it has higher numerical count than other, older elements and
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* thus emulate an an LRU-like behavior when deleting elements to free up space
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* in the page.
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*
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* When an element reaches it's max count of count_threshold, we try to poison
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* it by assuming that errors triggered count_threshold times in a single page
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* are excessive and that page shouldn't be used anymore. count_threshold is
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* initialized to COUNT_MASK which is the maximum.
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*
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* That error event entry causes cec_add_elem() to return !0 value and thus
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* signal to its callers to log the error.
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*
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* To the question why we've chosen a page and moving elements around with
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* memmove(), it is because it is a very simple structure to handle and max data
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* movement is 4K which on highly optimized modern CPUs is almost unnoticeable.
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* We wanted to avoid the pointer traversal of more complex structures like a
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* linked list or some sort of a balancing search tree.
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*
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* Deleting an element takes O(n) but since it is only a single page, it should
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* be fast enough and it shouldn't happen all too often depending on error
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* patterns.
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*/
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#undef pr_fmt
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#define pr_fmt(fmt) "RAS: " fmt
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/*
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* We use DECAY_BITS bits of PAGE_SHIFT bits for counting decay, i.e., how long
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* elements have stayed in the array without having been accessed again.
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*/
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#define DECAY_BITS 2
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#define DECAY_MASK ((1ULL << DECAY_BITS) - 1)
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#define MAX_ELEMS (PAGE_SIZE / sizeof(u64))
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/*
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* Threshold amount of inserted elements after which we start spring
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* cleaning.
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*/
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#define CLEAN_ELEMS (MAX_ELEMS >> DECAY_BITS)
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/* Bits which count the number of errors happened in this 4K page. */
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#define COUNT_BITS (PAGE_SHIFT - DECAY_BITS)
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#define COUNT_MASK ((1ULL << COUNT_BITS) - 1)
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#define FULL_COUNT_MASK (PAGE_SIZE - 1)
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/*
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* u64: [ 63 ... 12 | DECAY_BITS | COUNT_BITS ]
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*/
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#define PFN(e) ((e) >> PAGE_SHIFT)
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#define DECAY(e) (((e) >> COUNT_BITS) & DECAY_MASK)
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#define COUNT(e) ((unsigned int)(e) & COUNT_MASK)
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#define FULL_COUNT(e) ((e) & (PAGE_SIZE - 1))
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static struct ce_array {
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u64 *array; /* container page */
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unsigned int n; /* number of elements in the array */
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unsigned int decay_count; /*
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* number of element insertions/increments
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* since the last spring cleaning.
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*/
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u64 pfns_poisoned; /*
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* number of PFNs which got poisoned.
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*/
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u64 ces_entered; /*
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* The number of correctable errors
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* entered into the collector.
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*/
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u64 decays_done; /*
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* Times we did spring cleaning.
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*/
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union {
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struct {
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__u32 disabled : 1, /* cmdline disabled */
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__resv : 31;
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};
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__u32 flags;
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};
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} ce_arr;
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static DEFINE_MUTEX(ce_mutex);
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static u64 dfs_pfn;
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/* Amount of errors after which we offline */
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static unsigned int count_threshold = COUNT_MASK;
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/* Each element "decays" each decay_interval which is 24hrs by default. */
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#define CEC_DECAY_DEFAULT_INTERVAL 24 * 60 * 60 /* 24 hrs */
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#define CEC_DECAY_MIN_INTERVAL 1 * 60 * 60 /* 1h */
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#define CEC_DECAY_MAX_INTERVAL 30 * 24 * 60 * 60 /* one month */
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static struct delayed_work cec_work;
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static u64 decay_interval = CEC_DECAY_DEFAULT_INTERVAL;
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/*
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* Decrement decay value. We're using DECAY_BITS bits to denote decay of an
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* element in the array. On insertion and any access, it gets reset to max.
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*/
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static void do_spring_cleaning(struct ce_array *ca)
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{
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int i;
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for (i = 0; i < ca->n; i++) {
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u8 decay = DECAY(ca->array[i]);
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if (!decay)
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continue;
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decay--;
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ca->array[i] &= ~(DECAY_MASK << COUNT_BITS);
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ca->array[i] |= (decay << COUNT_BITS);
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}
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ca->decay_count = 0;
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ca->decays_done++;
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}
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/*
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* @interval in seconds
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*/
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static void cec_mod_work(unsigned long interval)
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{
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unsigned long iv;
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iv = interval * HZ;
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mod_delayed_work(system_wq, &cec_work, round_jiffies(iv));
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}
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static void cec_work_fn(struct work_struct *work)
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{
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mutex_lock(&ce_mutex);
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do_spring_cleaning(&ce_arr);
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mutex_unlock(&ce_mutex);
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cec_mod_work(decay_interval);
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}
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/*
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* @to: index of the smallest element which is >= then @pfn.
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*
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* Return the index of the pfn if found, otherwise negative value.
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*/
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static int __find_elem(struct ce_array *ca, u64 pfn, unsigned int *to)
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{
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int min = 0, max = ca->n - 1;
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u64 this_pfn;
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while (min <= max) {
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int i = (min + max) >> 1;
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this_pfn = PFN(ca->array[i]);
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if (this_pfn < pfn)
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min = i + 1;
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else if (this_pfn > pfn)
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max = i - 1;
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else if (this_pfn == pfn) {
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if (to)
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*to = i;
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return i;
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}
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}
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/*
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* When the loop terminates without finding @pfn, min has the index of
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* the element slot where the new @pfn should be inserted. The loop
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* terminates when min > max, which means the min index points to the
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* bigger element while the max index to the smaller element, in-between
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* which the new @pfn belongs to.
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*
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* For more details, see exercise 1, Section 6.2.1 in TAOCP, vol. 3.
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*/
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if (to)
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*to = min;
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return -ENOKEY;
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}
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static int find_elem(struct ce_array *ca, u64 pfn, unsigned int *to)
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{
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WARN_ON(!to);
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if (!ca->n) {
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*to = 0;
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return -ENOKEY;
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}
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return __find_elem(ca, pfn, to);
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}
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static void del_elem(struct ce_array *ca, int idx)
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{
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/* Save us a function call when deleting the last element. */
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if (ca->n - (idx + 1))
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memmove((void *)&ca->array[idx],
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(void *)&ca->array[idx + 1],
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(ca->n - (idx + 1)) * sizeof(u64));
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ca->n--;
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}
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static u64 del_lru_elem_unlocked(struct ce_array *ca)
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{
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unsigned int min = FULL_COUNT_MASK;
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int i, min_idx = 0;
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for (i = 0; i < ca->n; i++) {
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unsigned int this = FULL_COUNT(ca->array[i]);
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if (min > this) {
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min = this;
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min_idx = i;
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}
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}
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del_elem(ca, min_idx);
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return PFN(ca->array[min_idx]);
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}
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/*
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* We return the 0th pfn in the error case under the assumption that it cannot
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* be poisoned and excessive CEs in there are a serious deal anyway.
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*/
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static u64 __maybe_unused del_lru_elem(void)
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{
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struct ce_array *ca = &ce_arr;
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u64 pfn;
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if (!ca->n)
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return 0;
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mutex_lock(&ce_mutex);
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pfn = del_lru_elem_unlocked(ca);
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mutex_unlock(&ce_mutex);
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return pfn;
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}
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int cec_add_elem(u64 pfn)
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{
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struct ce_array *ca = &ce_arr;
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unsigned int to;
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int count, ret = 0;
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/*
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* We can be called very early on the identify_cpu() path where we are
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* not initialized yet. We ignore the error for simplicity.
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*/
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if (!ce_arr.array || ce_arr.disabled)
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return -ENODEV;
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mutex_lock(&ce_mutex);
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ca->ces_entered++;
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if (ca->n == MAX_ELEMS)
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WARN_ON(!del_lru_elem_unlocked(ca));
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ret = find_elem(ca, pfn, &to);
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if (ret < 0) {
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/*
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* Shift range [to-end] to make room for one more element.
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*/
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memmove((void *)&ca->array[to + 1],
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(void *)&ca->array[to],
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(ca->n - to) * sizeof(u64));
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ca->array[to] = (pfn << PAGE_SHIFT) |
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(DECAY_MASK << COUNT_BITS) | 1;
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ca->n++;
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ret = 0;
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goto decay;
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}
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count = COUNT(ca->array[to]);
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if (count < count_threshold) {
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ca->array[to] |= (DECAY_MASK << COUNT_BITS);
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ca->array[to]++;
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ret = 0;
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} else {
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u64 pfn = ca->array[to] >> PAGE_SHIFT;
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if (!pfn_valid(pfn)) {
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pr_warn("CEC: Invalid pfn: 0x%llx\n", pfn);
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} else {
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/* We have reached max count for this page, soft-offline it. */
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pr_err("Soft-offlining pfn: 0x%llx\n", pfn);
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memory_failure_queue(pfn, MF_SOFT_OFFLINE);
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ca->pfns_poisoned++;
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}
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del_elem(ca, to);
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/*
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* Return a >0 value to denote that we've reached the offlining
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* threshold.
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*/
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ret = 1;
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goto unlock;
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}
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decay:
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ca->decay_count++;
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if (ca->decay_count >= CLEAN_ELEMS)
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do_spring_cleaning(ca);
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unlock:
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mutex_unlock(&ce_mutex);
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return ret;
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}
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static int u64_get(void *data, u64 *val)
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{
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*val = *(u64 *)data;
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return 0;
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}
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static int pfn_set(void *data, u64 val)
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{
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*(u64 *)data = val;
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return cec_add_elem(val);
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}
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DEFINE_DEBUGFS_ATTRIBUTE(pfn_ops, u64_get, pfn_set, "0x%llx\n");
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static int decay_interval_set(void *data, u64 val)
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{
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*(u64 *)data = val;
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if (val < CEC_DECAY_MIN_INTERVAL)
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return -EINVAL;
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if (val > CEC_DECAY_MAX_INTERVAL)
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return -EINVAL;
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decay_interval = val;
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cec_mod_work(decay_interval);
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return 0;
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}
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DEFINE_DEBUGFS_ATTRIBUTE(decay_interval_ops, u64_get, decay_interval_set, "%lld\n");
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static int count_threshold_set(void *data, u64 val)
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{
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*(u64 *)data = val;
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if (val > COUNT_MASK)
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val = COUNT_MASK;
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count_threshold = val;
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return 0;
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}
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DEFINE_DEBUGFS_ATTRIBUTE(count_threshold_ops, u64_get, count_threshold_set, "%lld\n");
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static int array_dump(struct seq_file *m, void *v)
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{
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struct ce_array *ca = &ce_arr;
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u64 prev = 0;
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int i;
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mutex_lock(&ce_mutex);
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seq_printf(m, "{ n: %d\n", ca->n);
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for (i = 0; i < ca->n; i++) {
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u64 this = PFN(ca->array[i]);
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seq_printf(m, " %03d: [%016llx|%03llx]\n", i, this, FULL_COUNT(ca->array[i]));
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WARN_ON(prev > this);
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prev = this;
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}
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seq_printf(m, "}\n");
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seq_printf(m, "Stats:\nCEs: %llu\nofflined pages: %llu\n",
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ca->ces_entered, ca->pfns_poisoned);
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seq_printf(m, "Flags: 0x%x\n", ca->flags);
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seq_printf(m, "Decay interval: %lld seconds\n", decay_interval);
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seq_printf(m, "Decays: %lld\n", ca->decays_done);
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seq_printf(m, "Action threshold: %d\n", count_threshold);
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mutex_unlock(&ce_mutex);
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return 0;
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}
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static int array_open(struct inode *inode, struct file *filp)
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{
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return single_open(filp, array_dump, NULL);
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}
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static const struct file_operations array_ops = {
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.owner = THIS_MODULE,
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.open = array_open,
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.read = seq_read,
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.llseek = seq_lseek,
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.release = single_release,
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};
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static int __init create_debugfs_nodes(void)
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{
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struct dentry *d, *pfn, *decay, *count, *array;
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d = debugfs_create_dir("cec", ras_debugfs_dir);
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if (!d) {
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pr_warn("Error creating cec debugfs node!\n");
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return -1;
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}
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pfn = debugfs_create_file("pfn", S_IRUSR | S_IWUSR, d, &dfs_pfn, &pfn_ops);
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if (!pfn) {
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pr_warn("Error creating pfn debugfs node!\n");
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goto err;
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}
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array = debugfs_create_file("array", S_IRUSR, d, NULL, &array_ops);
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if (!array) {
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pr_warn("Error creating array debugfs node!\n");
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goto err;
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}
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decay = debugfs_create_file("decay_interval", S_IRUSR | S_IWUSR, d,
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&decay_interval, &decay_interval_ops);
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if (!decay) {
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pr_warn("Error creating decay_interval debugfs node!\n");
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goto err;
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}
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count = debugfs_create_file("count_threshold", S_IRUSR | S_IWUSR, d,
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&count_threshold, &count_threshold_ops);
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if (!count) {
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pr_warn("Error creating count_threshold debugfs node!\n");
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goto err;
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}
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return 0;
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err:
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debugfs_remove_recursive(d);
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return 1;
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}
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void __init cec_init(void)
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{
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if (ce_arr.disabled)
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return;
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ce_arr.array = (void *)get_zeroed_page(GFP_KERNEL);
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if (!ce_arr.array) {
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pr_err("Error allocating CE array page!\n");
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return;
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}
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if (create_debugfs_nodes())
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return;
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INIT_DELAYED_WORK(&cec_work, cec_work_fn);
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schedule_delayed_work(&cec_work, CEC_DECAY_DEFAULT_INTERVAL);
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pr_info("Correctable Errors collector initialized.\n");
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}
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int __init parse_cec_param(char *str)
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{
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if (!str)
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return 0;
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if (*str == '=')
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str++;
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if (!strcmp(str, "cec_disable"))
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ce_arr.disabled = 1;
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else
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return 0;
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|
return 1;
|
|
}
|