[PATCH v2] btrfs: add lockdep_assert_held to need_preemptive_reclaim

[PATCH v2] btrfs: add lockdep_assert_held to need_preemptive_reclaim

[Niels Dossche]

In a previous patch ("btrfs: extend locking to all space_info members
accesses") the locking for the space_info members was extended in
btrfs_preempt_reclaim_metadata_space because not all the member
accesses that needed locks were actually locked (bytes_pinned et al).

It was then suggested to also add a call to lockdep_assert_held to
need_preemptive_reclaim. This function also works with space_info
members. As of now, it has only two callsites which both hold the lock.
It was suggested to add this to be better safe than sorry regarding the
locking on bytes_pinned et al, in order to prevent similar issues in the
future.

Suggested-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Niels Dossche <dossche.niels@gmail.com>
---

Changes since v1:
 * Made commit message clearer
 * Changed initialization of thresh back to the original way

 fs/btrfs/space-info.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/btrfs/space-info.c b/fs/btrfs/space-info.c
index 294242c194d8..3122aad03e20 100644
--- a/fs/btrfs/space-info.c
+++ b/fs/btrfs/space-info.c
@@ -737,6 +737,8 @@ static bool need_preemptive_reclaim(struct btrfs_fs_info *fs_info,
 	u64 thresh = div_factor_fine(space_info->total_bytes, 90);
 	u64 used;
 
+	lockdep_assert_held(&space_info->lock);
+
 	/* If we're just plain full then async reclaim just slows us down. */
 	if ((space_info->bytes_used + space_info->bytes_reserved +
 	     global_rsv_size) >= thresh)
-- 
2.35.1

Re: [PATCH v2] btrfs: add lockdep_assert_held to need_preemptive_reclaim

[Johannes Thumshirn]

Looks good,
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>

Re: [PATCH v2] btrfs: add lockdep_assert_held to need_preemptive_reclaim

[David Sterba]

On Thu, Mar 03, 2022 at 01:38:39AM +0100, Niels Dossche wrote:
> In a previous patch ("btrfs: extend locking to all space_info members
> accesses") the locking for the space_info members was extended in
> btrfs_preempt_reclaim_metadata_space because not all the member
> accesses that needed locks were actually locked (bytes_pinned et al).
> 
> It was then suggested to also add a call to lockdep_assert_held to
> need_preemptive_reclaim. This function also works with space_info
> members. As of now, it has only two callsites which both hold the lock.
> It was suggested to add this to be better safe than sorry regarding the
> locking on bytes_pinned et al, in order to prevent similar issues in the
> future.
> 
> Suggested-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
> Signed-off-by: Niels Dossche <dossche.niels@gmail.com>

Added to misc-next, thanks.