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a47431dfb3
During reshape:
- reshape_request() advances rdev->recovery_offset for non-In_sync
devices locklessly.
- analyse_stripe() reads rdev->recovery_offset locklessly to decide:
a. use a replacement device to read ?
b. a device can already be treated as in-sync for the current
stripe ?
one possible scenario is:
CPU1 CPU2
reshape_request()
-> mddev->curr_resync_completed = sector_nr
-> if (!mddev->reshape_backwards)
-> rdev->recovery_offset = sector_nr
analyse_stripe(sh)
-> rdev = conf->disks[i].replacement
-> if (rdev->recovery_offset >=
sh->sector + stripe_sectors)
set_bit(R5_ReadRepl)
-> or
-> if (sh->sector + stripe_sectors <=
rdev->recovery_offset)
set_bit(R5_Insync)
And it could be:
- reading from a replacement before it is recovered far enough; or
- treating a not-yet-recovered device as in-sync for the current stripe.
Fixes: db0505d320 ("md: be cautious about using ->curr_resync_completed for ->recovery_offset")
The race report:
==================================================================
BUG: KCSAN: data-race in ops_run_io / reshape_request
write to 0xffff8bdee168b270 of 8 bytes by task 1704 on cpu 10:
reshape_request+0x1292/0x17b0
raid5_sync_request+0x815/0xa00
md_do_sync.cold+0xf8d/0x1516
[......]
read to 0xffff8bdee168b270 of 8 bytes by task 1696 on cpu 9:
ops_run_io+0xc25/0x1960
handle_stripe+0x2273/0x4570
handle_active_stripes.isra.0+0x6e0/0xa50
raid5d+0x7d5/0xb90
[......]
value changed: 0x0000000000091a00 -> 0x0000000000091b00
==================================================================
Signed-off-by: Chen Cheng <chencheng@fnnas.com>
Reviewed-by: Yu Kuai <yukuai@fygo.io>
Link: https://patch.msgid.link/20260627102519.136940-1-chencheng@fnnas.com
Signed-off-by: Yu Kuai <yukuai@fygo.io>
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