md/raid5: protect lockless recovery_offset accesses during reshape

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: db0505d32066 ("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>

0 files changed, 0 insertions, 0 deletions