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Btrfs: fix race during transaction joins

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While we're allocating ram for a new transaction, we drop our spinlock.
When we get the lock back, we do check to see if a transaction started
while we slept, but we don't check to make sure it isn't blocked
because a commit has already started.

Signed-off-by: Chris Mason <chris.mason@oracle.com>
This commit is contained in:
Chris Mason 2011-11-06 03:26:19 -05:00
parent 56d2a48f81
commit d43317dcd0
1 changed files with 8 additions and 5 deletions
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13
fs/btrfs/transaction.c
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@ -55,6 +55,7 @@ static noinline int join_transaction(struct btrfs_root *root, int nofail)
struct btrfs_transaction *cur_trans;
spin_lock(&root->fs_info->trans_lock);
loop:
if (root->fs_info->trans_no_join) {
if (!nofail) {
spin_unlock(&root->fs_info->trans_lock);
@ -75,16 +76,18 @@ static noinline int join_transaction(struct btrfs_root *root, int nofail)
cur_trans = kmem_cache_alloc(btrfs_transaction_cachep, GFP_NOFS);
if (!cur_trans)
return -ENOMEM;
spin_lock(&root->fs_info->trans_lock);
if (root->fs_info->running_transaction) {
/*
* someone started a transaction after we unlocked. Make sure
* to redo the trans_no_join checks above
*/
kmem_cache_free(btrfs_transaction_cachep, cur_trans);
cur_trans = root->fs_info->running_transaction;
atomic_inc(&cur_trans->use_count);
atomic_inc(&cur_trans->num_writers);
cur_trans->num_joined++;
spin_unlock(&root->fs_info->trans_lock);
return 0;
goto loop;
}
atomic_set(&cur_trans->num_writers, 1);
cur_trans->num_joined = 0;
init_waitqueue_head(&cur_trans->writer_wait);