public-mirrors/linux
1
0
Fork 0
mirror of git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git synced 2025-08-04 08:17:46 +00:00
Code Issues Projects Releases Packages Wiki Activity Actions

btrfs: get used bytes while holding lock at btrfs_reclaim_bgs_work()

Browse source 
At btrfs_reclaim_bgs_work(), we are grabbing twice the used bytes counter
of the block group while not holding the block group's spinlock. This can
result in races, reported by KCSAN and similar tools, since a concurrent
task can be updating that counter while at btrfs_update_block_group().

So avoid these races by grabbing the counter in a critical section
delimited by the block group's spinlock after setting the block group to
RO mode. This also avoids using two different values of the counter in
case it changes in between each read. This silences KCSAN and is required
for the next patch in the series too.

Fixes: 243192b676 ("btrfs: report reclaim stats in sysfs")
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
Filipe Manana 2025-02-24 15:40:26 +00:00 • committed by David Sterba
parent 1283b8c125
commit ba5d06440c
1 changed files with 16 additions and 5 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

21
fs/btrfs/block-group.c
View file

@ -1823,7 +1823,7 @@ void btrfs_reclaim_bgs_work(struct work_struct *work)
list_sort(NULL, &fs_info->reclaim_bgs, reclaim_bgs_cmp);
while (!list_empty(&fs_info->reclaim_bgs)) {
u64 zone_unusable;
u64 reclaimed;
u64 used;
int ret = 0;
bg = list_first_entry(&fs_info->reclaim_bgs,
@ -1919,19 +1919,30 @@ void btrfs_reclaim_bgs_work(struct work_struct *work)
if (ret < 0)
goto next;
/*
* Grab the used bytes counter while holding the block group's
* spinlock to prevent races with tasks concurrently updating it
* due to extent allocation and deallocation (running
* btrfs_update_block_group()) - we have set the block group to
* RO but that only prevents extent reservation, allocation
* happens after reservation.
*/
spin_lock(&bg->lock);
used = bg->used;
spin_unlock(&bg->lock);
btrfs_info(fs_info,
"reclaiming chunk %llu with %llu%% used %llu%% unusable",
bg->start,
div64_u64(bg->used * 100, bg->length),
div64_u64(used * 100, bg->length),
div64_u64(zone_unusable * 100, bg->length));
trace_btrfs_reclaim_block_group(bg);
reclaimed = bg->used;
ret = btrfs_relocate_chunk(fs_info, bg->start);
if (ret) {
btrfs_dec_block_group_ro(bg);
btrfs_err(fs_info, "error relocating chunk %llu",
bg->start);
reclaimed = 0;
used = 0;
spin_lock(&space_info->lock);
space_info->reclaim_errors++;
if (READ_ONCE(space_info->periodic_reclaim))
@ -1940,7 +1951,7 @@ void btrfs_reclaim_bgs_work(struct work_struct *work)
}
spin_lock(&space_info->lock);
space_info->reclaim_count++;
space_info->reclaim_bytes += reclaimed;
space_info->reclaim_bytes += used;
spin_unlock(&space_info->lock);
next: