btrfs: add correction to handle -1 edge case in async discard (81b29a3b) · Commits · 戴 / test

From Dave's testing described below, it's possible to drive a file system to have bogus values of discardable_extents and _bytes. As btrfs_discard_calc_delay() is the only user of discardable_extents, we can correct here for any negative discardable_extents/discardable_bytes. The problem is not reliably reproducible. The workload that created it was based on linux git tree, switching between release tags, then everytihng deleted followed by a full rebalance. At this state the values of discardable_bytes was 16K and discardable_extents was -1, expected values 0 and 0. Repeating the workload again did not correct the bogus values so the offset seems to be stable once it happens. Reported-by:

David Sterba <dsterba@suse.com> Signed-off-by:

Dennis Zhou <dennis@kernel.org> Signed-off-by:

David Sterba <dsterba@suse.com>

fs/btrfs/discard.c

+22 −0

Original line number	Diff line number	Diff line
		@@ -516,6 +516,7 @@ bool btrfs_run_discard_work(struct btrfs_discard_ctl *discard_ctl)
		void btrfs_discard_calc_delay(struct btrfs_discard_ctl *discard_ctl)
		{
		s32 discardable_extents;
		s64 discardable_bytes;
		u32 iops_limit;
		unsigned long delay;
		unsigned long lower_limit = BTRFS_DISCARD_MIN_DELAY_MSEC;
		@@ -526,6 +527,27 @@ void btrfs_discard_calc_delay(struct btrfs_discard_ctl *discard_ctl)

		spin_lock(&discard_ctl->lock);

		/*
		* The following is to fix a potential -1 discrepenancy that we're not
		* sure how to reproduce. But given that this is the only place that
		* utilizes these numbers and this is only called by from
		* btrfs_finish_extent_commit() which is synchronized, we can correct
		* here.
		*/
		if (discardable_extents < 0)
		atomic_add(-discardable_extents,
		&discard_ctl->discardable_extents);

		discardable_bytes = atomic64_read(&discard_ctl->discardable_bytes);
		if (discardable_bytes < 0)
		atomic64_add(-discardable_bytes,
		&discard_ctl->discardable_bytes);

		if (discardable_extents <= 0) {
		spin_unlock(&discard_ctl->lock);
		return;
		}

		iops_limit = READ_ONCE(discard_ctl->iops_limit);
		if (iops_limit)
		lower_limit = max_t(unsigned long, lower_limit,

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