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Lei Xue e1dfa986fd cachefiles: Fix race between read_waiter and read_copier involving op->to_do 
[ Upstream commit 7bb0c53384 ]

There is a potential race in fscache operation enqueuing for reading and
copying multiple pages from cachefiles to netfs.  The problem can be seen
easily on a heavy loaded system (for example many processes reading files
continually on an NFS share covered by fscache triggered this problem within
a few minutes).

The race is due to cachefiles_read_waiter() adding the op to the monitor
to_do list and then then drop the object->work_lock spinlock before
completing fscache_enqueue_operation().  Once the lock is dropped,
cachefiles_read_copier() grabs the op, completes processing it, and
makes it through fscache_retrieval_complete() which sets the op->state to
the final state of FSCACHE_OP_ST_COMPLETE(4).  When cachefiles_read_waiter()
finally gets through the remainder of fscache_enqueue_operation()
it sees the invalid state, and hits the ASSERTCMP and the following
oops is seen:
[ 2259.612361] FS-Cache:
[ 2259.614785] FS-Cache: Assertion failed
[ 2259.618639] FS-Cache: 4 == 5 is false
[ 2259.622456] ------------[ cut here ]------------
[ 2259.627190] kernel BUG at fs/fscache/operation.c:70!
...
[ 2259.791675] RIP: 0010:[<ffffffffc061b4cf>]  [<ffffffffc061b4cf>] fscache_enqueue_operation+0xff/0x170 [fscache]
[ 2259.802059] RSP: 0000:ffffa0263d543be0  EFLAGS: 00010046
[ 2259.807521] RAX: 0000000000000019 RBX: ffffa01a4d390480 RCX: 0000000000000006
[ 2259.814847] RDX: 0000000000000000 RSI: 0000000000000046 RDI: ffffa0263d553890
[ 2259.822176] RBP: ffffa0263d543be8 R08: 0000000000000000 R09: ffffa0263c2d8708
[ 2259.829502] R10: 0000000000001e7f R11: 0000000000000000 R12: ffffa01a4d390480
[ 2259.844483] R13: ffff9fa9546c5920 R14: ffffa0263d543c80 R15: ffffa0293ff9bf10
[ 2259.859554] FS:  00007f4b6efbd700(0000) GS:ffffa0263d540000(0000) knlGS:0000000000000000
[ 2259.875571] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 2259.889117] CR2: 00007f49e1624ff0 CR3: 0000012b38b38000 CR4: 00000000007607e0
[ 2259.904015] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 2259.918764] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 2259.933449] PKRU: 55555554
[ 2259.943654] Call Trace:
[ 2259.953592]  <IRQ>
[ 2259.955577]  [<ffffffffc03a7c12>] cachefiles_read_waiter+0x92/0xf0 [cachefiles]
[ 2259.978039]  [<ffffffffa34d3942>] __wake_up_common+0x82/0x120
[ 2259.991392]  [<ffffffffa34d3a63>] __wake_up_common_lock+0x83/0xc0
[ 2260.004930]  [<ffffffffa34d3510>] ? task_rq_unlock+0x20/0x20
[ 2260.017863]  [<ffffffffa34d3ab3>] __wake_up+0x13/0x20
[ 2260.030230]  [<ffffffffa34c72a0>] __wake_up_bit+0x50/0x70
[ 2260.042535]  [<ffffffffa35bdcdb>] unlock_page+0x2b/0x30
[ 2260.054495]  [<ffffffffa35bdd09>] page_endio+0x29/0x90
[ 2260.066184]  [<ffffffffa368fc81>] mpage_end_io+0x51/0x80

CPU1
cachefiles_read_waiter()
 20 static int cachefiles_read_waiter(wait_queue_entry_t *wait, unsigned mode,
 21                                   int sync, void *_key)
 22 {
...
 61         spin_lock(&object->work_lock);
 62         list_add_tail(&monitor->op_link, &op->to_do);
 63         spin_unlock(&object->work_lock);
<begin race window>
 64
 65         fscache_enqueue_retrieval(op);
182 static inline void fscache_enqueue_retrieval(struct fscache_retrieval *op)
183 {
184         fscache_enqueue_operation(&op->op);
185 }
 58 void fscache_enqueue_operation(struct fscache_operation *op)
 59 {
 60         struct fscache_cookie *cookie = op->object->cookie;
 61
 62         _enter("{OBJ%x OP%x,%u}",
 63                op->object->debug_id, op->debug_id, atomic_read(&op->usage));
 64
 65         ASSERT(list_empty(&op->pend_link));
 66         ASSERT(op->processor != NULL);
 67         ASSERT(fscache_object_is_available(op->object));
 68         ASSERTCMP(atomic_read(&op->usage), >, 0);
<end race window>

CPU2
cachefiles_read_copier()
168         while (!list_empty(&op->to_do)) {
...
202                 fscache_end_io(op, monitor->netfs_page, error);
203                 put_page(monitor->netfs_page);
204                 fscache_retrieval_complete(op, 1);

CPU1
 58 void fscache_enqueue_operation(struct fscache_operation *op)
 59 {
...
 69         ASSERTIFCMP(op->state != FSCACHE_OP_ST_IN_PROGRESS,
 70                     op->state, ==,  FSCACHE_OP_ST_CANCELLED);

Signed-off-by: Lei Xue <carmark.dlut@gmail.com>
Signed-off-by: Dave Wysochanski <dwysocha@redhat.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
 		2020-06-03 08:21:11 +02:00
Documentation USB: hub: Revert commit bd0e6c9614 ("usb: hub: try old enumeration scheme first for high speed devices") 2020-04-29 16:33:14 +02:00
LICENSES LICENSES: Rename other to deprecated 2019-05-03 06:34:32 -06:00
arch ARM: dts: rockchip: fix pinctrl sub nodename for spi in rk322x.dtsi 2020-06-03 08:21:08 +02:00
block iocost: protect iocg->abs_vdebt with iocg->waitq.lock 2020-05-14 07:58:27 +02:00
certs PKCS#7: Refactor verify_pkcs7_signature() 2019-08-05 18:40:18 -04:00
crypto gcc-10: avoid shadowing standard library 'free()' in crypto 2020-05-20 08:20:29 +02:00
drivers drm/amdgpu: Use GEM obj reference for KFD BOs 2020-06-03 08:21:11 +02:00
fs cachefiles: Fix race between read_waiter and read_copier involving op->to_do 2020-06-03 08:21:11 +02:00
include net/tls: fix race condition causing kernel panic 2020-06-03 08:21:01 +02:00
init x86: Fix early boot crash on gcc-10, third try 2020-05-20 08:20:34 +02:00
ipc ipc/util.c: sysvipc_find_ipc() incorrectly updates position index 2020-05-20 08:20:16 +02:00
kernel sched/fair: Fix enqueue_task_fair() warning some more 2020-05-27 17:46:52 +02:00
lib vsprintf: don't obfuscate NULL and error pointers 2020-05-27 17:46:43 +02:00
mm kasan: disable branch tracing for core runtime 2020-05-27 17:46:48 +02:00
net net/tls: free record only on encryption error 2020-06-03 08:21:06 +02:00
samples vmalloc: fix remap_vmalloc_range() bounds checks 2020-04-29 16:33:14 +02:00
scripts kbuild: Remove debug info from kallsyms linking 2020-05-27 17:46:44 +02:00
security apparmor: Fix aa_label refcnt leak in policy_update 2020-05-27 17:46:42 +02:00
sound ALSA: usb-audio: add mapping for ASRock TRX40 Creator 2020-06-03 08:21:09 +02:00
tools KVM: selftests: Fix build for evmcs.h 2020-05-27 17:46:36 +02:00
usr initramfs: restore default compression behavior 2020-04-08 09:08:38 +02:00
virt KVM: arm: vgic: Synchronize the whole guest on GIC{D,R}_I{S,C}ACTIVER read 2020-05-20 08:20:04 +02:00
.clang-format clang-format: Update with the latest for_each macro list 2019-08-31 10:00:51 +02:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore Modules updates for v5.4 2019-09-22 10:34:46 -07:00
.mailmap ARM: SoC fixes 2019-11-10 13:41:59 -08:00
COPYING COPYING: use the new text with points to the license files 2018-03-23 12:41:45 -06:00
CREDITS MAINTAINERS: Remove Simon as Renesas SoC Co-Maintainer 2019-10-10 08:12:51 -07:00
Kbuild kbuild: do not descend to ./Kbuild when cleaning 2019-08-21 21:03:58 +09:00
Kconfig docs: kbuild: convert docs to ReST and rename to *.rst 2019-06-14 14:21:21 -06:00
MAINTAINERS MAINTAINERS: Update drm/i915 bug filing URL 2020-02-28 17:22:19 +01:00
Makefile Linux 5.4.43 2020-05-27 17:46:53 +02:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.