Linux 6.9+ is unable to start a degraded RAID1 array with one drive,
when that drive has a write-mostly flag set. During such an attempt,
the following assertion in bio_split() is hit:
BUG_ON(sectors <= 0);
Call Trace:
? bio_split+0x96/0xb0
? exc_invalid_op+0x53/0x70
? bio_split+0x96/0xb0
? asm_exc_invalid_op+0x1b/0x20
? bio_split+0x96/0xb0
? raid1_read_request+0x890/0xd20
? __call_rcu_common.constprop.0+0x97/0x260
raid1_make_request+0x81/0xce0
? __get_random_u32_below+0x17/0x70
? new_slab+0x2b3/0x580
md_handle_request+0x77/0x210
md_submit_bio+0x62/0xa0
__submit_bio+0x17b/0x230
submit_bio_noacct_nocheck+0x18e/0x3c0
submit_bio_noacct+0x244/0x670
After investigation, it turned out that choose_slow_rdev() does not set
the value of max_sectors in some cases and because of it,
raid1_read_request calls bio_split with sectors == 0.
Fix it by filling in this variable.
This bug was introduced in
commit dfa8ecd167 ("md/raid1: factor out choose_slow_rdev() from read_balance()")
but apparently hidden until
commit 0091c5a269 ("md/raid1: factor out helpers to choose the best rdev from read_balance()")
shortly thereafter.
Cc: stable@vger.kernel.org # 6.9.x+
Signed-off-by: Mateusz Jończyk <mat.jonczyk@o2.pl>
Fixes: dfa8ecd167 ("md/raid1: factor out choose_slow_rdev() from read_balance()")
Cc: Song Liu <song@kernel.org>
Cc: Yu Kuai <yukuai3@huawei.com>
Cc: Paul Luse <paul.e.luse@linux.intel.com>
Cc: Xiao Ni <xni@redhat.com>
Cc: Mariusz Tkaczyk <mariusz.tkaczyk@linux.intel.com>
Link: https://lore.kernel.org/linux-raid/20240706143038.7253-1-mat.jonczyk@o2.pl/
--
Tested on both Linux 6.10 and 6.9.8.
Inside a VM, mdadm testsuite for RAID1 on 6.10 did not find any problems:
./test --dev=loop --no-error --raidtype=raid1
(on 6.9.8 there was one failure, caused by external bitmap support not
compiled in).
Notes:
- I was reliably getting deadlocks when adding / removing devices
on such an array - while the array was loaded with fsstress with 20
concurrent processes. When the array was idle or loaded with fsstress
with 8 processes, no such deadlocks happened in my tests.
This occurred also on unpatched Linux 6.8.0 though, but not on
6.1.97-rc1, so this is likely an independent regression (to be
investigated).
- I was also getting deadlocks when adding / removing the bitmap on the
array in similar conditions - this happened on Linux 6.1.97-rc1
also though. fsstress with 8 concurrent processes did cause it only
once during many tests.
- in my testing, there was once a problem with hot adding an
internal bitmap to the array:
mdadm: Cannot add bitmap while array is resyncing or reshaping etc.
mdadm: failed to set internal bitmap.
even though no such reshaping was happening according to /proc/mdstat.
This seems unrelated, though.
Reviewed-by: Yu Kuai <yukuai3@huawei.com>
Signed-off-by: Song Liu <song@kernel.org>
Link: https://lore.kernel.org/r/20240711202316.10775-1-mat.jonczyk@o2.pl
36a5c03f23