summaryrefslogtreecommitdiff
diff options
context:
space:
mode:
authorGuoju Fang <fangguoju@gmail.com>2019-11-13 16:03:16 +0800
committerJens Axboe <axboe@kernel.dk>2019-11-13 15:42:50 -0700
commit34cf78bf34d48dddddfeeadb44f9841d7864997a (patch)
treed6010b3ea9defa5300f679f4fe8bd55d85ebd2bd
parentc0e0954e909c17b43d176ab219fc598964616ae6 (diff)
bcache: fix a lost wake-up problem caused by mca_cannibalize_lock
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>
-rw-r--r--drivers/md/bcache/bcache.h1
-rw-r--r--drivers/md/bcache/btree.c12
-rw-r--r--drivers/md/bcache/super.c1
3 files changed, 10 insertions, 4 deletions
diff --git a/drivers/md/bcache/bcache.h b/drivers/md/bcache/bcache.h
index 013e35a9e317..3653faf3bf48 100644
--- a/drivers/md/bcache/bcache.h
+++ b/drivers/md/bcache/bcache.h
@@ -582,6 +582,7 @@ struct cache_set {
*/
wait_queue_head_t btree_cache_wait;
struct task_struct *btree_cache_alloc_lock;
+ spinlock_t btree_cannibalize_lock;
/*
* When we free a btree node, we increment the gen of the bucket the
diff --git a/drivers/md/bcache/btree.c b/drivers/md/bcache/btree.c
index 00523cd1db80..39d7fc1ef1ee 100644
--- a/drivers/md/bcache/btree.c
+++ b/drivers/md/bcache/btree.c
@@ -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,
diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
index 20ed838e9413..ebb854ed05a4 100644
--- a/drivers/md/bcache/super.c
+++ b/drivers/md/bcache/super.c
@@ -1769,6 +1769,7 @@ struct cache_set *bch_cache_set_alloc(struct cache_sb *sb)
sema_init(&c->sb_write_mutex, 1);
mutex_init(&c->bucket_lock);
init_waitqueue_head(&c->btree_cache_wait);
+ spin_lock_init(&c->btree_cannibalize_lock);
init_waitqueue_head(&c->bucket_wait);
init_waitqueue_head(&c->gc_wait);
sema_init(&c->uuid_write_mutex, 1);