Re: dm: use queue_limits_set

[Mike Snitzer <snitzer@kernel.org>]

On Mon, May 20, 2024 at 06:03:11PM -0400, Mike Snitzer wrote:
> On Mon, May 20, 2024 at 10:12:37PM +0200, Christoph Hellwig wrote:
> > On Mon, May 20, 2024 at 01:17:46PM -0400, Mike Snitzer wrote:
> > > Doubt there was anything in fstests setting max discard user limit
> > > (max_user_discard_sectors) in Ted's case. blk_set_stacking_limits()
> > > sets max_user_discard_sectors to UINT_MAX, so given the use of
> > > min(lim->max_hw_discard_sectors, lim->max_user_discard_sectors) I
> > > suspect blk_stack_limits() stacks up max_discard_sectors to match the
> > > underlying storage's max_hw_discard_sectors.
> > > 
> > > And max_hw_discard_sectors exceeds BIO_PRISON_MAX_RANGE, resulting in
> > > dm_cell_key_has_valid_range() triggering on:
> > > WARN_ON_ONCE(key->block_end - key->block_begin > BIO_PRISON_MAX_RANGE)
> > 
> > Oh, that makes more sense.
> > 
> > I think you just want to set the max_hw_discard_sectors limit before
> > stacking in the lower device limits so that they can only lower it.
> > 
> > (and in the long run we should just stop stacking the limits except
> > for request based dm which really needs it)
> 
> This is what I staged, I cannot send a patch out right now.. 
> 
> Ted if you need the patch in email (rather than from linux-dm.git) I
> can send it later tonight.  Please see:
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm.git/commit/?h=dm-6.10&id=825d8bbd2f32cb229c3b6653bd454832c3c20acb

From: Mike Snitzer <snitzer@kernel.org>
Date: Mon, 20 May 2024 13:34:06 -0400
Subject: [PATCH] dm: always manage discard support in terms of max_hw_discard_sectors

Commit 4f563a64732d ("block: add a max_user_discard_sectors queue
limit") changed block core to set max_discard_sectors to:
 min(lim->max_hw_discard_sectors, lim->max_user_discard_sectors)

Since commit 1c0e720228ad ("dm: use queue_limits_set") it was reported
dm-thinp was failing in a few fstests (generic/347 and generic/405)
with the first WARN_ON_ONCE in dm_cell_key_has_valid_range() being
reported, e.g.:
WARNING: CPU: 1 PID: 30 at drivers/md/dm-bio-prison-v1.c:128 dm_cell_key_has_valid_range+0x3d/0x50

blk_set_stacking_limits() sets max_user_discard_sectors to UINT_MAX,
so given how block core now sets max_discard_sectors (detailed above)
it follows that blk_stack_limits() stacks up the underlying device's
max_hw_discard_sectors and max_discard_sectors is set to match it. If
max_hw_discard_sectors exceeds dm's BIO_PRISON_MAX_RANGE, then
dm_cell_key_has_valid_range() will trigger the warning with:
WARN_ON_ONCE(key->block_end - key->block_begin > BIO_PRISON_MAX_RANGE)

Aside from this warning, the discard will fail.  Fix this and other DM
issues by governing discard support in terms of max_hw_discard_sectors
instead of max_discard_sectors.

Reported-by: Theodore Ts'o <tytso@mit.edu>
Fixes: 1c0e720228ad ("dm: use queue_limits_set")
Signed-off-by: Mike Snitzer <snitzer@kernel.org>
---
 drivers/md/dm-cache-target.c | 5 ++---
 drivers/md/dm-clone-target.c | 4 ++--
 drivers/md/dm-log-writes.c   | 2 +-
 drivers/md/dm-snap.c         | 2 +-
 drivers/md/dm-target.c       | 1 -
 drivers/md/dm-thin.c         | 4 ++--
 drivers/md/dm-zero.c         | 1 -
 drivers/md/dm-zoned-target.c | 1 -
 drivers/md/dm.c              | 2 +-
 9 files changed, 9 insertions(+), 13 deletions(-)

diff --git a/drivers/md/dm-cache-target.c b/drivers/md/dm-cache-target.c
index 911f73f7ebba..1f0bc1173230 100644
--- a/drivers/md/dm-cache-target.c
+++ b/drivers/md/dm-cache-target.c
@@ -3394,8 +3394,8 @@ static void set_discard_limits(struct cache *cache, struct queue_limits *limits)
 
 	if (!cache->features.discard_passdown) {
 		/* No passdown is done so setting own virtual limits */
-		limits->max_discard_sectors = min_t(sector_t, cache->discard_block_size * 1024,
-						    cache->origin_sectors);
+		limits->max_hw_discard_sectors = min_t(sector_t, cache->discard_block_size * 1024,
+						       cache->origin_sectors);
 		limits->discard_granularity = cache->discard_block_size << SECTOR_SHIFT;
 		return;
 	}
@@ -3404,7 +3404,6 @@ static void set_discard_limits(struct cache *cache, struct queue_limits *limits)
 	 * cache_iterate_devices() is stacking both origin and fast device limits
 	 * but discards aren't passed to fast device, so inherit origin's limits.
 	 */
-	limits->max_discard_sectors = origin_limits->max_discard_sectors;
 	limits->max_hw_discard_sectors = origin_limits->max_hw_discard_sectors;
 	limits->discard_granularity = origin_limits->discard_granularity;
 	limits->discard_alignment = origin_limits->discard_alignment;
diff --git a/drivers/md/dm-clone-target.c b/drivers/md/dm-clone-target.c
index 94b2fc33f64b..2332d9798141 100644
--- a/drivers/md/dm-clone-target.c
+++ b/drivers/md/dm-clone-target.c
@@ -2050,7 +2050,8 @@ static void set_discard_limits(struct clone *clone, struct queue_limits *limits)
 	if (!test_bit(DM_CLONE_DISCARD_PASSDOWN, &clone->flags)) {
 		/* No passdown is done so we set our own virtual limits */
 		limits->discard_granularity = clone->region_size << SECTOR_SHIFT;
-		limits->max_discard_sectors = round_down(UINT_MAX >> SECTOR_SHIFT, clone->region_size);
+		limits->max_hw_discard_sectors = round_down(UINT_MAX >> SECTOR_SHIFT,
+							    clone->region_size);
 		return;
 	}
 
@@ -2059,7 +2060,6 @@ static void set_discard_limits(struct clone *clone, struct queue_limits *limits)
 	 * device limits but discards aren't passed to the source device, so
 	 * inherit destination's limits.
 	 */
-	limits->max_discard_sectors = dest_limits->max_discard_sectors;
 	limits->max_hw_discard_sectors = dest_limits->max_hw_discard_sectors;
 	limits->discard_granularity = dest_limits->discard_granularity;
 	limits->discard_alignment = dest_limits->discard_alignment;
diff --git a/drivers/md/dm-log-writes.c b/drivers/md/dm-log-writes.c
index f17a6cf2284e..8d7df8303d0a 100644
--- a/drivers/md/dm-log-writes.c
+++ b/drivers/md/dm-log-writes.c
@@ -871,7 +871,7 @@ static void log_writes_io_hints(struct dm_target *ti, struct queue_limits *limit
 	if (!bdev_max_discard_sectors(lc->dev->bdev)) {
 		lc->device_supports_discard = false;
 		limits->discard_granularity = lc->sectorsize;
-		limits->max_discard_sectors = (UINT_MAX >> SECTOR_SHIFT);
+		limits->max_hw_discard_sectors = (UINT_MAX >> SECTOR_SHIFT);
 	}
 	limits->logical_block_size = bdev_logical_block_size(lc->dev->bdev);
 	limits->physical_block_size = bdev_physical_block_size(lc->dev->bdev);
diff --git a/drivers/md/dm-snap.c b/drivers/md/dm-snap.c
index 0ace06d1bee3..f40c18da4000 100644
--- a/drivers/md/dm-snap.c
+++ b/drivers/md/dm-snap.c
@@ -2410,7 +2410,7 @@ static void snapshot_io_hints(struct dm_target *ti, struct queue_limits *limits)
 
 		/* All discards are split on chunk_size boundary */
 		limits->discard_granularity = snap->store->chunk_size;
-		limits->max_discard_sectors = snap->store->chunk_size;
+		limits->max_hw_discard_sectors = snap->store->chunk_size;
 
 		up_read(&_origins_lock);
 	}
diff --git a/drivers/md/dm-target.c b/drivers/md/dm-target.c
index 0c4efb0bef8a..652627aea11b 100644
--- a/drivers/md/dm-target.c
+++ b/drivers/md/dm-target.c
@@ -249,7 +249,6 @@ static int io_err_iterate_devices(struct dm_target *ti,
 
 static void io_err_io_hints(struct dm_target *ti, struct queue_limits *limits)
 {
-	limits->max_discard_sectors = UINT_MAX;
 	limits->max_hw_discard_sectors = UINT_MAX;
 	limits->discard_granularity = 512;
 }
diff --git a/drivers/md/dm-thin.c b/drivers/md/dm-thin.c
index 4793ad2aa1f7..e0528a4f809c 100644
--- a/drivers/md/dm-thin.c
+++ b/drivers/md/dm-thin.c
@@ -4100,7 +4100,7 @@ static void pool_io_hints(struct dm_target *ti, struct queue_limits *limits)
 	if (pt->adjusted_pf.discard_enabled) {
 		disable_discard_passdown_if_not_supported(pt);
 		if (!pt->adjusted_pf.discard_passdown)
-			limits->max_discard_sectors = 0;
+			limits->max_hw_discard_sectors = 0;
 		/*
 		 * The pool uses the same discard limits as the underlying data
 		 * device.  DM core has already set this up.
@@ -4497,7 +4497,7 @@ static void thin_io_hints(struct dm_target *ti, struct queue_limits *limits)
 
 	if (pool->pf.discard_enabled) {
 		limits->discard_granularity = pool->sectors_per_block << SECTOR_SHIFT;
-		limits->max_discard_sectors = pool->sectors_per_block * BIO_PRISON_MAX_RANGE;
+		limits->max_hw_discard_sectors = pool->sectors_per_block * BIO_PRISON_MAX_RANGE;
 	}
 }
 
diff --git a/drivers/md/dm-zero.c b/drivers/md/dm-zero.c
index 3b13e6eb1aa4..9a0bb623e823 100644
--- a/drivers/md/dm-zero.c
+++ b/drivers/md/dm-zero.c
@@ -61,7 +61,6 @@ static int zero_map(struct dm_target *ti, struct bio *bio)
 
 static void zero_io_hints(struct dm_target *ti, struct queue_limits *limits)
 {
-	limits->max_discard_sectors = UINT_MAX;
 	limits->max_hw_discard_sectors = UINT_MAX;
 	limits->discard_granularity = 512;
 }
diff --git a/drivers/md/dm-zoned-target.c b/drivers/md/dm-zoned-target.c
index 621794a9edd6..12236e6f46f3 100644
--- a/drivers/md/dm-zoned-target.c
+++ b/drivers/md/dm-zoned-target.c
@@ -1001,7 +1001,6 @@ static void dmz_io_hints(struct dm_target *ti, struct queue_limits *limits)
 
 	limits->discard_alignment = 0;
 	limits->discard_granularity = DMZ_BLOCK_SIZE;
-	limits->max_discard_sectors = chunk_sectors;
 	limits->max_hw_discard_sectors = chunk_sectors;
 	limits->max_write_zeroes_sectors = chunk_sectors;
 
diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 7d0746b37c8e..3adfc6b83c01 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -1086,7 +1086,7 @@ void disable_discard(struct mapped_device *md)
 	struct queue_limits *limits = dm_get_queue_limits(md);
 
 	/* device doesn't really support DISCARD, disable it */
-	limits->max_discard_sectors = 0;
+	limits->max_hw_discard_sectors = 0;
 }
 
 void disable_write_zeroes(struct mapped_device *md)
-- 
2.44.0