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md/raid5: validate discard support at request time

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Raid5 used to disable discard limits when devices_handle_discard_safely
was not set or when stacked member limits could not support a full-stripe
discard. That hides discard from userspace before raid5 can decide whether
a request can be handled safely.

Follow other virtual drivers and advertise a UINT_MAX discard limit for the
md device. Cache lower discard support in r5conf when setting queue limits,
and reject unsupported discard bios before queuing stripe work.

Link: https://patch.msgid.link/20260605072639.2434847-3-yukuai@kernel.org
Signed-off-by: Yu Kuai <yukuai@fygo.io>
This commit is contained in:
Yu Kuai
2026-06-05 15:26:38 +08:00
parent 74ddbf98e2
commit 9057309267
2 changed files with 20 additions and 15 deletions
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34
drivers/md/raid5.c
View File

@@ -1134,6 +1134,18 @@ static void defer_issue_bios(struct r5conf *conf, sector_t sector,
dispatch_bio_list(&tmp);
}
static bool raid5_discard_limits(struct mddev *mddev, struct bio *bi)
{
struct r5conf *conf = mddev->private;
if (!conf->raid5_discard_unsupported)
return true;
bi->bi_status = BLK_STS_NOTSUPP;
bio_endio(bi);
return false;
}
static void
raid5_end_read_request(struct bio *bi);
static void
@@ -5704,6 +5716,9 @@ static void make_discard_request(struct mddev *mddev, struct bio *bi)
/* Skip discard while reshape is happening */
return;
if (!raid5_discard_limits(mddev, bi))
return;
stripe_sectors = conf->chunk_sectors *
(conf->raid_disks - conf->max_degraded);
first_stripe = DIV_ROUND_UP_SECTOR_T(bi->bi_iter.bi_sector,
@@ -7817,24 +7832,12 @@ static int raid5_set_limits(struct mddev *mddev)
queue_limits_stack_bdev(&lim, rdev->bdev, rdev->new_data_offset,
mddev->gendisk->disk_name);
/*
* Zeroing is required for discard, otherwise data could be lost.
*
* Consider a scenario: discard a stripe (the stripe could be
* inconsistent if discard_zeroes_data is 0); write one disk of the
* stripe (the stripe could be inconsistent again depending on which
* disks are used to calculate parity); the disk is broken; The stripe
* data of this disk is lost.
*
* We only allow DISCARD if the sysadmin has confirmed that only safe
* devices are in use by setting a module parameter. A better idea
* might be to turn DISCARD into WRITE_ZEROES requests, as that is
* required to be safe.
*/
if (!devices_handle_discard_safely ||
lim.max_discard_sectors < (stripe >> 9) ||
lim.discard_granularity < stripe)
lim.max_hw_discard_sectors = 0;
conf->raid5_discard_unsupported = true;
else
conf->raid5_discard_unsupported = false;
/*
* Requests require having a bitmap for each stripe.
@@ -7843,6 +7846,7 @@ static int raid5_set_limits(struct mddev *mddev)
lim.max_hw_sectors = RAID5_MAX_REQ_STRIPES << RAID5_STRIPE_SHIFT(conf);
if ((lim.max_hw_sectors << 9) < lim.io_opt)
lim.max_hw_sectors = lim.io_opt >> 9;
lim.max_hw_discard_sectors = UINT_MAX;
/* No restrictions on the number of segments in the request */
lim.max_segments = USHRT_MAX;

1
drivers/md/raid5.h
View File

@@ -689,6 +689,7 @@ struct r5conf {
struct list_head pending_list;
int pending_data_cnt;
struct r5pending_data *next_pending_data;
bool raid5_discard_unsupported;
mempool_t *ctx_pool;
int ctx_size;