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authorLei Xue <carmark.dlut@gmail.com>2020-05-07 15:50:22 +0300
committerDavid Howells <dhowells@redhat.com>2020-05-09 01:01:10 +0300
commit7bb0c5338436dae953622470d52689265867f032 (patch)
tree9e24dfe5255bdbe644f058c9401d1d3079428cb1 /fs/cachefiles
parent50eaa652b54df1e2b48dc398d9e6114c9ed080eb (diff)
downloadlinux-7bb0c5338436dae953622470d52689265867f032.tar.xz
cachefiles: Fix race between read_waiter and read_copier involving op->to_do
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>
Diffstat (limited to 'fs/cachefiles')
-rw-r--r--fs/cachefiles/rdwr.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/fs/cachefiles/rdwr.c b/fs/cachefiles/rdwr.c
index d3d78176b23c..e7726f5f1241 100644
--- a/fs/cachefiles/rdwr.c
+++ b/fs/cachefiles/rdwr.c
@@ -60,9 +60,9 @@ static int cachefiles_read_waiter(wait_queue_entry_t *wait, unsigned mode,
object = container_of(op->op.object, struct cachefiles_object, fscache);
spin_lock(&object->work_lock);
list_add_tail(&monitor->op_link, &op->to_do);
+ fscache_enqueue_retrieval(op);
spin_unlock(&object->work_lock);
- fscache_enqueue_retrieval(op);
fscache_put_retrieval(op);
return 0;
}