From cf749823857230017c86504bfdc70524f929ba96 Mon Sep 17 00:00:00 2001 From: Josef Bacik Date: Wed, 1 Oct 2008 19:11:18 -0400 Subject: [PATCH] Btrfs: fix deadlock between alloc_mutex/chunk_mutex This fixes a deadlock that happens between the alloc_mutex and chunk_mutex. Process A comes in, decides to do a do_chunk_alloc, which takes the chunk_mutex, and is holding the alloc_mutex because the only way you get to do_chunk_alloc is by holding the alloc_mutex. btrfs_alloc_chunk does its thing and goes to insert a new item, which results in a cow of the block. We get into del_pending_extents from there, where if we need to be rescheduled we drop the alloc_mutex and schedule. At this point process B comes in to do an allocation and gets the alloc_mutex, and because process A did not do the chunk allocation completely it thinks its a good time to do a chunk allocation as well, and hangs on the chunk_mutex. Process A wakes up and tries to take the alloc_mutex and cannot. The way to fix this is do a mutex_trylock() on chunk_mutex. If we return 0 we didn't get the lock, and if this is just a "hey it may be a good time to allocate a chunk" then we just exit. If we are trying to force an allocation then we reschedule and keep trying to acquire the chunk_mutex. If once we acquire it the space is already full then we can just exit, otherwise we can continue with the chunk allocation. Thank you, Signed-off-by: Josef Bacik --- fs/btrfs/extent-tree.c | 15 +++++++++++++-- 1 file changed, 13 insertions(+), 2 deletions(-) diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c index 677d5e774fa..db37b867e4f 100644 --- a/fs/btrfs/extent-tree.c +++ b/fs/btrfs/extent-tree.c @@ -1505,7 +1505,7 @@ static int do_chunk_alloc(struct btrfs_trans_handle *trans, u64 thresh; u64 start; u64 num_bytes; - int ret = 0; + int ret = 0, waited = 0; flags = reduce_alloc_profile(extent_root, flags); @@ -1530,7 +1530,18 @@ static int do_chunk_alloc(struct btrfs_trans_handle *trans, space_info->bytes_reserved + alloc_bytes) < thresh) goto out; - mutex_lock(&extent_root->fs_info->chunk_mutex); + while (!mutex_trylock(&extent_root->fs_info->chunk_mutex)) { + if (!force) + goto out; + mutex_unlock(&extent_root->fs_info->alloc_mutex); + cond_resched(); + mutex_lock(&extent_root->fs_info->alloc_mutex); + waited = 1; + } + + if (waited && space_info->full) + goto out_unlock; + ret = btrfs_alloc_chunk(trans, extent_root, &start, &num_bytes, flags); if (ret == -ENOSPC) { printk("space info full %Lu\n", flags); -- 2.39.3