| Message ID | 984c070461f31182e87d1b4f27c4565088a31b40.1616595693.git.naohiro.aota@wdc.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | btrfs: zoned: move log tree node allocation out of log_root_tree->log_mutex | expand |
On Wed, Mar 24, 2021 at 2:26 PM Naohiro Aota <naohiro.aota@wdc.com> wrote: > > Commit 6e37d2459941 ("btrfs: zoned: fix deadlock on log sync") pointed out > a deadlock warning and removed > mutex_{lock,unlock}(&fs_info->tree_root->log_mutex). While it looks like it > always cause a deadlock, we didn't see actual deadlock in fstests runs. The > reason is log_root_tree->log_mutex != fs_info->tree_root->log_mutex, not > taking the same lock. So, the warning was actually a false-positive. > > Since btrfs_alloc_log_tree_node() is protected only by > fs_info->tree_root->log_mutex, we can (and should) move the code out of the > lock scope of log_root_tree->log_mutex and silence the warning. > > Cc: Filipe Manana <fdmanana@suse.com> > Cc: Johannes Thumshirn <johannes.thumshirn@wdc.com> > Signed-off-by: Naohiro Aota <naohiro.aota@wdc.com> Reviewed-by: Filipe Manana <fdmanana@suse.com> Looks good, thanks. > --- > fs/btrfs/tree-log.c | 12 +++++++----- > 1 file changed, 7 insertions(+), 5 deletions(-) > > diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c > index 92a368627791..72c4b66ed516 100644 > --- a/fs/btrfs/tree-log.c > +++ b/fs/btrfs/tree-log.c > @@ -3165,20 +3165,22 @@ int btrfs_sync_log(struct btrfs_trans_handle *trans, > */ > mutex_unlock(&root->log_mutex); > > - btrfs_init_log_ctx(&root_log_ctx, NULL); > - > - mutex_lock(&log_root_tree->log_mutex); > - > if (btrfs_is_zoned(fs_info)) { > + mutex_lock(&fs_info->tree_root->log_mutex); > if (!log_root_tree->node) { > ret = btrfs_alloc_log_tree_node(trans, log_root_tree); > if (ret) { > - mutex_unlock(&log_root_tree->log_mutex); > + mutex_unlock(&fs_info->tree_log_mutex); > goto out; > } > } > + mutex_unlock(&fs_info->tree_root->log_mutex); > } > > + btrfs_init_log_ctx(&root_log_ctx, NULL); > + > + mutex_lock(&log_root_tree->log_mutex); > + > index2 = log_root_tree->log_transid % 2; > list_add_tail(&root_log_ctx.list, &log_root_tree->log_ctxs[index2]); > root_log_ctx.log_transid = log_root_tree->log_transid; > -- > 2.31.0 >
Looks good,
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
On Wed, Mar 24, 2021 at 11:23:11PM +0900, Naohiro Aota wrote: > Commit 6e37d2459941 ("btrfs: zoned: fix deadlock on log sync") pointed out > a deadlock warning and removed > mutex_{lock,unlock}(&fs_info->tree_root->log_mutex). While it looks like it > always cause a deadlock, we didn't see actual deadlock in fstests runs. The > reason is log_root_tree->log_mutex != fs_info->tree_root->log_mutex, not > taking the same lock. So, the warning was actually a false-positive. > > Since btrfs_alloc_log_tree_node() is protected only by > fs_info->tree_root->log_mutex, we can (and should) move the code out of the > lock scope of log_root_tree->log_mutex and silence the warning. > > Cc: Filipe Manana <fdmanana@suse.com> > Cc: Johannes Thumshirn <johannes.thumshirn@wdc.com> > Signed-off-by: Naohiro Aota <naohiro.aota@wdc.com> Added to misc-next, thanks.
diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c index 92a368627791..72c4b66ed516 100644 --- a/fs/btrfs/tree-log.c +++ b/fs/btrfs/tree-log.c @@ -3165,20 +3165,22 @@ int btrfs_sync_log(struct btrfs_trans_handle *trans, */ mutex_unlock(&root->log_mutex); - btrfs_init_log_ctx(&root_log_ctx, NULL); - - mutex_lock(&log_root_tree->log_mutex); - if (btrfs_is_zoned(fs_info)) { + mutex_lock(&fs_info->tree_root->log_mutex); if (!log_root_tree->node) { ret = btrfs_alloc_log_tree_node(trans, log_root_tree); if (ret) { - mutex_unlock(&log_root_tree->log_mutex); + mutex_unlock(&fs_info->tree_log_mutex); goto out; } } + mutex_unlock(&fs_info->tree_root->log_mutex); } + btrfs_init_log_ctx(&root_log_ctx, NULL); + + mutex_lock(&log_root_tree->log_mutex); + index2 = log_root_tree->log_transid % 2; list_add_tail(&root_log_ctx.list, &log_root_tree->log_ctxs[index2]); root_log_ctx.log_transid = log_root_tree->log_transid;
Commit 6e37d2459941 ("btrfs: zoned: fix deadlock on log sync") pointed out a deadlock warning and removed mutex_{lock,unlock}(&fs_info->tree_root->log_mutex). While it looks like it always cause a deadlock, we didn't see actual deadlock in fstests runs. The reason is log_root_tree->log_mutex != fs_info->tree_root->log_mutex, not taking the same lock. So, the warning was actually a false-positive. Since btrfs_alloc_log_tree_node() is protected only by fs_info->tree_root->log_mutex, we can (and should) move the code out of the lock scope of log_root_tree->log_mutex and silence the warning. Cc: Filipe Manana <fdmanana@suse.com> Cc: Johannes Thumshirn <johannes.thumshirn@wdc.com> Signed-off-by: Naohiro Aota <naohiro.aota@wdc.com> --- fs/btrfs/tree-log.c | 12 +++++++----- 1 file changed, 7 insertions(+), 5 deletions(-)