From: Jason Baron jbaron@akamai.com
commit e836007089ba8fdf24e636ef2b007651fb4582e6 upstream.
We've found that using raid0 with the 'original' layout and discard enabled with different disk sizes (such that at least two zones are created) can result in data corruption. This is due to the fact that the discard handling in 'raid0_handle_discard()' assumes the 'alternate' layout. We've seen this corruption using ext4 but other filesystems are likely susceptible as well.
More specifically, while multiple zones are necessary to create the corruption, the corruption may not occur with multiple zones if they layout in such a way the layout matches what the 'alternate' layout would have produced. Thus, not all raid0 devices with the 'original' layout, different size disks and discard enabled will encounter this corruption.
The 3.14 kernel inadvertently changed the raid0 disk layout for different size disks. Thus, running a pre-3.14 kernel and post-3.14 kernel on the same raid0 array could corrupt data. This lead to the creation of the 'original' layout (to match the pre-3.14 layout) and the 'alternate' layout (to match the post 3.14 layout) in the 5.4 kernel time frame and an option to tell the kernel which layout to use (since it couldn't be autodetected). However, when the 'original' layout was added back to 5.4 discard support for the 'original' layout was not added leading this issue.
I've been able to reliably reproduce the corruption with the following test case:
1. create raid0 array with different size disks using original layout 2. mkfs 3. mount -o discard 4. create lots of files 5. remove 1/2 the files 6. fstrim -a (or just the mount point for the raid0 array) 7. umount 8. fsck -fn /dev/md0 (spews all sorts of corruptions)
Let's fix this by adding proper discard support to the 'original' layout. The fix 'maps' the 'original' layout disks to the order in which they are read/written such that we can compare the disks in the same way that the current 'alternate' layout does. A 'disk_shift' field is added to 'struct strip_zone'. This could be computed on the fly in raid0_handle_discard() but by adding this field, we save some computation in the discard path.
Note we could also potentially fix this by re-ordering the disks in the zones that follow the first one, and then always read/writing them using the 'alternate' layout. However, that is seen as a more substantial change, and we are attempting the least invasive fix at this time to remedy the corruption.
I've verified the change using the reproducer mentioned above. Typically, the corruption is seen after less than 3 iterations, while the patch has run 500+ iterations.
Cc: NeilBrown neilb@suse.de Cc: Song Liu song@kernel.org Fixes: c84a1372df92 ("md/raid0: avoid RAID0 data corruption due to layout confusion.") Cc: stable@vger.kernel.org Signed-off-by: Jason Baron jbaron@akamai.com Signed-off-by: Song Liu song@kernel.org Link: https://lore.kernel.org/r/20230623180523.1901230-1-jbaron@akamai.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/md/raid0.c | 62 ++++++++++++++++++++++++++++++++++++++++++++++------- drivers/md/raid0.h | 1 2 files changed, 55 insertions(+), 8 deletions(-)
--- a/drivers/md/raid0.c +++ b/drivers/md/raid0.c @@ -270,6 +270,18 @@ static int create_strip_zones(struct mdd goto abort; }
+ if (conf->layout == RAID0_ORIG_LAYOUT) { + for (i = 1; i < conf->nr_strip_zones; i++) { + sector_t first_sector = conf->strip_zone[i-1].zone_end; + + sector_div(first_sector, mddev->chunk_sectors); + zone = conf->strip_zone + i; + /* disk_shift is first disk index used in the zone */ + zone->disk_shift = sector_div(first_sector, + zone->nb_dev); + } + } + pr_debug("md/raid0:%s: done.\n", mdname(mddev)); *private_conf = conf;
@@ -431,6 +443,20 @@ exit_acct_set: return ret; }
+/* + * Convert disk_index to the disk order in which it is read/written. + * For example, if we have 4 disks, they are numbered 0,1,2,3. If we + * write the disks starting at disk 3, then the read/write order would + * be disk 3, then 0, then 1, and then disk 2 and we want map_disk_shift() + * to map the disks as follows 0,1,2,3 => 1,2,3,0. So disk 0 would map + * to 1, 1 to 2, 2 to 3, and 3 to 0. That way we can compare disks in + * that 'output' space to understand the read/write disk ordering. + */ +static int map_disk_shift(int disk_index, int num_disks, int disk_shift) +{ + return ((disk_index + num_disks - disk_shift) % num_disks); +} + static void raid0_handle_discard(struct mddev *mddev, struct bio *bio) { struct r0conf *conf = mddev->private; @@ -444,7 +470,9 @@ static void raid0_handle_discard(struct sector_t end_disk_offset; unsigned int end_disk_index; unsigned int disk; + sector_t orig_start, orig_end;
+ orig_start = start; zone = find_zone(conf, &start);
if (bio_end_sector(bio) > zone->zone_end) { @@ -458,6 +486,7 @@ static void raid0_handle_discard(struct } else end = bio_end_sector(bio);
+ orig_end = end; if (zone != conf->strip_zone) end = end - zone[-1].zone_end;
@@ -469,13 +498,26 @@ static void raid0_handle_discard(struct last_stripe_index = end; sector_div(last_stripe_index, stripe_size);
- start_disk_index = (int)(start - first_stripe_index * stripe_size) / - mddev->chunk_sectors; + /* In the first zone the original and alternate layouts are the same */ + if ((conf->layout == RAID0_ORIG_LAYOUT) && (zone != conf->strip_zone)) { + sector_div(orig_start, mddev->chunk_sectors); + start_disk_index = sector_div(orig_start, zone->nb_dev); + start_disk_index = map_disk_shift(start_disk_index, + zone->nb_dev, + zone->disk_shift); + sector_div(orig_end, mddev->chunk_sectors); + end_disk_index = sector_div(orig_end, zone->nb_dev); + end_disk_index = map_disk_shift(end_disk_index, + zone->nb_dev, zone->disk_shift); + } else { + start_disk_index = (int)(start - first_stripe_index * stripe_size) / + mddev->chunk_sectors; + end_disk_index = (int)(end - last_stripe_index * stripe_size) / + mddev->chunk_sectors; + } start_disk_offset = ((int)(start - first_stripe_index * stripe_size) % mddev->chunk_sectors) + first_stripe_index * mddev->chunk_sectors; - end_disk_index = (int)(end - last_stripe_index * stripe_size) / - mddev->chunk_sectors; end_disk_offset = ((int)(end - last_stripe_index * stripe_size) % mddev->chunk_sectors) + last_stripe_index * mddev->chunk_sectors; @@ -483,18 +525,22 @@ static void raid0_handle_discard(struct for (disk = 0; disk < zone->nb_dev; disk++) { sector_t dev_start, dev_end; struct md_rdev *rdev; + int compare_disk; + + compare_disk = map_disk_shift(disk, zone->nb_dev, + zone->disk_shift);
- if (disk < start_disk_index) + if (compare_disk < start_disk_index) dev_start = (first_stripe_index + 1) * mddev->chunk_sectors; - else if (disk > start_disk_index) + else if (compare_disk > start_disk_index) dev_start = first_stripe_index * mddev->chunk_sectors; else dev_start = start_disk_offset;
- if (disk < end_disk_index) + if (compare_disk < end_disk_index) dev_end = (last_stripe_index + 1) * mddev->chunk_sectors; - else if (disk > end_disk_index) + else if (compare_disk > end_disk_index) dev_end = last_stripe_index * mddev->chunk_sectors; else dev_end = end_disk_offset; --- a/drivers/md/raid0.h +++ b/drivers/md/raid0.h @@ -6,6 +6,7 @@ struct strip_zone { sector_t zone_end; /* Start of the next zone (in sectors) */ sector_t dev_start; /* Zone offset in real dev (in sectors) */ int nb_dev; /* # of devices attached to the zone */ + int disk_shift; /* start disk for the original layout */ };
/* Linux 3.14 (20d0189b101) made an unintended change to