[PATCH] btrfs: extend locking to all space_info members accesses

[PATCH] btrfs: extend locking to all space_info members accesses

[Niels Dossche]

bytes_pinned is always accessed under space_info->lock, except in
btrfs_preempt_reclaim_metadata_space, however the other members are
accessed under that lock. The reserved member of the rsv's are also
partially accessed under a lock and partially not. Move all these
accesses into the same lock to ensure consistency.

Signed-off-by: Niels Dossche <niels.dossche@ugent.be>
Signed-off-by: Niels Dossche <dossche.niels@gmail.com>
---
 fs/btrfs/space-info.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/btrfs/space-info.c b/fs/btrfs/space-info.c
index 294242c194d8..62382ae1eb02 100644
--- a/fs/btrfs/space-info.c
+++ b/fs/btrfs/space-info.c
@@ -1061,7 +1061,6 @@ static void btrfs_preempt_reclaim_metadata_space(struct work_struct *work)
 			trans_rsv->reserved;
 		if (block_rsv_size < space_info->bytes_may_use)
 			delalloc_size = space_info->bytes_may_use - block_rsv_size;
-		spin_unlock(&space_info->lock);
 
 		/*
 		 * We don't want to include the global_rsv in our calculation,
@@ -1092,6 +1091,8 @@ static void btrfs_preempt_reclaim_metadata_space(struct work_struct *work)
 			flush = FLUSH_DELAYED_REFS_NR;
 		}
 
+		spin_unlock(&space_info->lock);
+
 		/*
 		 * We don't want to reclaim everything, just a portion, so scale
 		 * down the to_reclaim by 1/4.  If it takes us down to 0,
-- 
2.35.1

Re: [PATCH] btrfs: extend locking to all space_info members accesses

[Johannes Thumshirn]

On 25/02/2022 22:21, Niels Dossche wrote:
> bytes_pinned is always accessed under space_info->lock, except in
> btrfs_preempt_reclaim_metadata_space, however the other members are
> accessed under that lock. The reserved member of the rsv's are also
> partially accessed under a lock and partially not. Move all these
> accesses into the same lock to ensure consistency.

Maybe also add a lockdep_assert_held() call to need_preemptive_reclaim().

As of now, it has only two callsites which both hold the lock before
accessing bytes_pinned et al, but better safe then sorry.

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

Re: [PATCH] btrfs: extend locking to all space_info members accesses

[Josef Bacik]

On Fri, Feb 25, 2022 at 10:20:28PM +0100, Niels Dossche wrote:
> bytes_pinned is always accessed under space_info->lock, except in
> btrfs_preempt_reclaim_metadata_space, however the other members are
> accessed under that lock. The reserved member of the rsv's are also
> partially accessed under a lock and partially not. Move all these
> accesses into the same lock to ensure consistency.
> 
> Signed-off-by: Niels Dossche <niels.dossche@ugent.be>
> Signed-off-by: Niels Dossche <dossche.niels@gmail.com>

Reviewed-by: Josef Bacik <josef@toxicpanda.com>

Thanks,

Josef

Re: [PATCH] btrfs: extend locking to all space_info members accesses

[David Sterba]

On Fri, Feb 25, 2022 at 10:20:28PM +0100, Niels Dossche wrote:
> bytes_pinned is always accessed under space_info->lock, except in
> btrfs_preempt_reclaim_metadata_space, however the other members are
> accessed under that lock. The reserved member of the rsv's are also
> partially accessed under a lock and partially not. Move all these
> accesses into the same lock to ensure consistency.
> 
> Signed-off-by: Niels Dossche <niels.dossche@ugent.be>
> Signed-off-by: Niels Dossche <dossche.niels@gmail.com>

Added to misc-next, thanks.