On 3/16/18 4:12 PM, David Sterba wrote: > On Fri, Mar 16, 2018 at 02:36:27PM -0400, [email protected] wrote: >> From: Jeff Mahoney <[email protected]> >> >> While running btrfs/011, I hit the following lockdep splat. >> >> This is the important bit: >> pcpu_alloc+0x1ac/0x5e0 >> __percpu_counter_init+0x4e/0xb0 >> btrfs_init_fs_root+0x99/0x1c0 [btrfs] >> btrfs_get_fs_root.part.54+0x5b/0x150 [btrfs] >> resolve_indirect_refs+0x130/0x830 [btrfs] >> find_parent_nodes+0x69e/0xff0 [btrfs] >> btrfs_find_all_roots_safe+0xa0/0x110 [btrfs] >> btrfs_find_all_roots+0x50/0x70 [btrfs] >> btrfs_qgroup_prepare_account_extents+0x53/0x90 [btrfs] >> btrfs_commit_transaction+0x3ce/0x9b0 [btrfs] >> >> The percpu_counter_init call in btrfs_alloc_subvolume_writers >> uses GFP_KERNEL, which we can't do during transaction commit. >> >> This switches it to GFP_NOFS. > >> Signed-off-by: Jeff Mahoney <[email protected]> >> --- >> fs/btrfs/disk-io.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c >> index 21f34ad0d411..eb6bb3169a9e 100644 >> --- a/fs/btrfs/disk-io.c >> +++ b/fs/btrfs/disk-io.c >> @@ -1108,7 +1108,7 @@ static struct btrfs_subvolume_writers >> *btrfs_alloc_subvolume_writers(void) >> if (!writers) >> return ERR_PTR(-ENOMEM); >> >> - ret = percpu_counter_init(&writers->counter, 0, GFP_KERNEL); >> + ret = percpu_counter_init(&writers->counter, 0, GFP_NOFS); > > A line above the diff context is another allocation that does GFP_NOFS, > so one of the gfp flags were wrong. > > Looks like there's another instance where percpu allocates with > GFP_KERNEL: create_space_info that can be called from the path that > allocates chunks, so this also looks like a NOFS candidate.
We can get rid of this case entirely. Those call sites should be removed since the space_infos are all allocated at mount time. -Jeff -- Jeff Mahoney SUSE Labs
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