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x86, mce: fix a race condition in mce_read()

Browse source 
Impact: bugfix

Considering the situation as follow:

before: mcelog.next == 1, mcelog.entry[0].finished = 1

+--------------------------------------------------------------------------
R                   W1                  W2                  W3

read mcelog.next (1)
                    mcelog.next++ (2)
                    (working on entry 1,
                    finished == 0)

mcelog.next = 0
                                        mcelog.next++ (1)
                                        (working on entry 0)
                                                           mcelog.next++ (2)
                                                           (working on entry 1)
                        <----------------- race ---------------->
                    (done on entry 1,
                    finished = 1)
                                                           (done on entry 1,
                                                           finished = 1)

To fix the race condition, a cmpxchg loop is added to mce_read() to
ensure no new MCE record can be added between mcelog.next reading and
mcelog.next = 0.

Signed-off-by: Huang Ying <ying.huang@intel.com>
Signed-off-by: Andi Kleen <ak@linux.intel.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
This commit is contained in:
Huang Ying 2009-02-12 13:39:34 +01:00 committed by H. Peter Anvin
parent d6b75584a3
commit ef41df4344
1 changed files with 23 additions and 16 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

39
arch/x86/kernel/cpu/mcheck/mce_64.c
View file

@ -595,7 +595,7 @@ static ssize_t mce_read(struct file *filp, char __user *ubuf, size_t usize,
{
unsigned long *cpu_tsc;
static DEFINE_MUTEX(mce_read_mutex);
unsigned next;
unsigned prev, next;
char __user *buf = ubuf;
int i, err;
@ -614,25 +614,32 @@ static ssize_t mce_read(struct file *filp, char __user *ubuf, size_t usize,
}
err = 0;
for (i = 0; i < next; i++) {
unsigned long start = jiffies;
prev = 0;
do {
for (i = prev; i < next; i++) {
unsigned long start = jiffies;
while (!mcelog.entry[i].finished) {
if (time_after_eq(jiffies, start + 2)) {
memset(mcelog.entry + i,0, sizeof(struct mce));
goto timeout;
while (!mcelog.entry[i].finished) {
if (time_after_eq(jiffies, start + 2)) {
memset(mcelog.entry + i, 0,
sizeof(struct mce));
goto timeout;
}
cpu_relax();
}
cpu_relax();
smp_rmb();
err |= copy_to_user(buf, mcelog.entry + i,
sizeof(struct mce));
buf += sizeof(struct mce);
timeout:
;
}
smp_rmb();
err |= copy_to_user(buf, mcelog.entry + i, sizeof(struct mce));
buf += sizeof(struct mce);
timeout:
;
}
memset(mcelog.entry, 0, next * sizeof(struct mce));
mcelog.next = 0;
memset(mcelog.entry + prev, 0,
(next - prev) * sizeof(struct mce));
prev = next;
next = cmpxchg(&mcelog.next, prev, 0);
} while (next != prev);
synchronize_sched();