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bcache: fix a lost wake-up problem caused by mca_cannibalize_lock

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This patch fix a lost wake-up problem caused by the race between
mca_cannibalize_lock and bch_cannibalize_unlock.

Consider two processes, A and B. Process A is executing
mca_cannibalize_lock, while process B takes c->btree_cache_alloc_lock
and is executing bch_cannibalize_unlock. The problem happens that after
process A executes cmpxchg and will execute prepare_to_wait. In this
timeslice process B executes wake_up, but after that process A executes
prepare_to_wait and set the state to TASK_INTERRUPTIBLE. Then process A
goes to sleep but no one will wake up it. This problem may cause bcache
device to dead.

Signed-off-by: Guoju Fang <fangguoju@gmail.com>
Signed-off-by: Coly Li <colyli@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Guoju Fang
2019-11-13 16:03:16 +08:00
committed by Jens Axboe
parent c0e0954e90
commit 34cf78bf34
3 changed files with 10 additions and 4 deletions
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12
drivers/md/bcache/btree.c
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@@ -910,15 +910,17 @@ out:
static int mca_cannibalize_lock(struct cache_set *c, struct btree_op *op)
{
struct task_struct *old;
old = cmpxchg(&c->btree_cache_alloc_lock, NULL, current);
if (old && old != current) {
spin_lock(&c->btree_cannibalize_lock);
if (likely(c->btree_cache_alloc_lock == NULL)) {
c->btree_cache_alloc_lock = current;
} else if (c->btree_cache_alloc_lock != current) {
if (op)
prepare_to_wait(&c->btree_cache_wait, &op->wait,
TASK_UNINTERRUPTIBLE);
spin_unlock(&c->btree_cannibalize_lock);
return -EINTR;
}
spin_unlock(&c->btree_cannibalize_lock);
return 0;
}
@@ -953,10 +955,12 @@ static struct btree *mca_cannibalize(struct cache_set *c, struct btree_op *op,
*/
static void bch_cannibalize_unlock(struct cache_set *c)
{
spin_lock(&c->btree_cannibalize_lock);
if (c->btree_cache_alloc_lock == current) {
c->btree_cache_alloc_lock = NULL;
wake_up(&c->btree_cache_wait);
}
spin_unlock(&c->btree_cannibalize_lock);
}
static struct btree *mca_alloc(struct cache_set *c, struct btree_op *op,