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btrfs: don't call btrfs_start_delalloc_roots in flushoncommit 

We're holding the sb_start_intwrite lock at this point, and doing async
filemap_flush of the inodes will result in a deadlock if we freeze the
fs during this operation.  This is because we could do a
btrfs_join_transaction() in the thread we are waiting on which would
block at sb_start_intwrite, and thus deadlock.  Using
writeback_inodes_sb() side steps the problem by not introducing all of
these extra locking dependencies.

Signed-off-by: Josef Bacik <jbacik@fb.com>
Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
Josef Bacik 2017-10-19 14:16:01 -04:00 committed by David Sterba
parent 0e0adbcfdc
commit ce8ea7cc6e
1 changed files with 10 additions and 1 deletions
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11
fs/btrfs/transaction.c
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@ -1916,8 +1916,17 @@ static void cleanup_transaction(struct btrfs_trans_handle *trans,
static inline int btrfs_start_delalloc_flush(struct btrfs_fs_info *fs_info)
{
/*
* We use writeback_inodes_sb here because if we used
* btrfs_start_delalloc_roots we would deadlock with fs freeze.
* Currently are holding the fs freeze lock, if we do an async flush
* we'll do btrfs_join_transaction() and deadlock because we need to
* wait for the fs freeze lock. Using the direct flushing we benefit
* from already being in a transaction and our join_transaction doesn't
* have to re-take the fs freeze lock.
*/
if (btrfs_test_opt(fs_info, FLUSHONCOMMIT))
return btrfs_start_delalloc_roots(fs_info, 1, -1);
writeback_inodes_sb(fs_info->sb, WB_REASON_SYNC);
return 0;
}