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| author | Sage Weil <sage@newdream.net> | 2010-10-29 23:37:34 +0400 |
|---|---|---|
| committer | Chris Mason <chris.mason@oracle.com> | 2010-10-29 23:37:34 +0400 |
| commit | 99d16cbcaf694c803a1b6bf7e851694ffe1d255d (patch) | |
| tree | dacf7f8eca75dc0d92566b5d3876f3efe8196e35 | |
| parent | fccdae435c1b295cca546f23f6f43126a28ffac3 (diff) | |
| download | linux-99d16cbcaf694c803a1b6bf7e851694ffe1d255d.tar.xz | |
Btrfs: fix deadlock in btrfs_commit_transaction
We calculate timeout (either 1 or MAX_SCHEDULE_TIMEOUT) based on whether
num_writers > 1 or should_grow at the top of the loop. Then, much much
later, we wait for that timeout if either num_writers or should_grow is
true. However, it's possible for a racing process (calling
btrfs_end_transaction()) to decrement num_writers such that we wait
forever instead of for 1.
Fix this by deciding how long to wait when we wait. Include a smp_mb()
before checking if the waitqueue is active to ensure the num_writers
is visible.
Signed-off-by: Sage Weil <sage@newdream.net>
Signed-off-by: Chris Mason <chris.mason@oracle.com>
| -rw-r--r-- | fs/btrfs/transaction.c | 13 |
1 files changed, 5 insertions, 8 deletions
diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c index 325d9a5f0128..700dc4b34ada 100644 --- a/fs/btrfs/transaction.c +++ b/fs/btrfs/transaction.c @@ -402,6 +402,7 @@ static int __btrfs_end_transaction(struct btrfs_trans_handle *trans, WARN_ON(cur_trans->num_writers < 1); cur_trans->num_writers--; + smp_mb(); if (waitqueue_active(&cur_trans->writer_wait)) wake_up(&cur_trans->writer_wait); put_transaction(cur_trans); @@ -1010,7 +1011,6 @@ int btrfs_commit_transaction(struct btrfs_trans_handle *trans, struct btrfs_root *root) { unsigned long joined = 0; - unsigned long timeout = 1; struct btrfs_transaction *cur_trans; struct btrfs_transaction *prev_trans = NULL; DEFINE_WAIT(wait); @@ -1081,11 +1081,6 @@ int btrfs_commit_transaction(struct btrfs_trans_handle *trans, snap_pending = 1; WARN_ON(cur_trans != trans->transaction); - if (cur_trans->num_writers > 1) - timeout = MAX_SCHEDULE_TIMEOUT; - else if (should_grow) - timeout = 1; - mutex_unlock(&root->fs_info->trans_mutex); if (flush_on_commit || snap_pending) { @@ -1107,8 +1102,10 @@ int btrfs_commit_transaction(struct btrfs_trans_handle *trans, TASK_UNINTERRUPTIBLE); smp_mb(); - if (cur_trans->num_writers > 1 || should_grow) - schedule_timeout(timeout); + if (cur_trans->num_writers > 1) + schedule_timeout(MAX_SCHEDULE_TIMEOUT); + else if (should_grow) + schedule_timeout(1); mutex_lock(&root->fs_info->trans_mutex); finish_wait(&cur_trans->writer_wait, &wait); |