On 2025/4/16 20:22, Mikulas Patocka wrote:
On Wed, 16 Apr 2025, LongPing Wei wrote:
A BUG was reported as below when CONFIG_DEBUG_ATOMIC_SLEEP and
try_verify_in_tasklet are enabled.
diff --git a/drivers/md/dm-bufio.c b/drivers/md/dm-bufio.c
index 9c8ed65cd87e..bdbd79e76f96 100644
--- a/drivers/md/dm-bufio.c
+++ b/drivers/md/dm-bufio.c
@@ -2424,6 +2424,10 @@ static void __scan(struct dm_bufio_client *c)
atomic_long_dec(&c->need_shrink);
freed++;
+
+ if (static_branch_unlikely(&no_sleep_enabled) &&
c->no_sleep)
+ continue;
+
cond_resched();
}
}
--
2.34.1
Hi
Thanks for the bug report. I think it is not a good practice in general to
hold a spinlock and loop over a list of unbounded size. So, I modified
your patch so that it drops the lock after every 16 iterations and calls
cond_resched() with the lock dropped.
Please, test this patch and report whether it works for you.
Mikulas
[PATCH] dm-bufio: don't schedule in atomic context
A BUG was reported as below when CONFIG_DEBUG_ATOMIC_SLEEP and
try_verify_in_tasklet are enabled.
[ 129.444685][ T934] BUG: sleeping function called from invalid context at
drivers/md/dm-bufio.c:2421
[ 129.444723][ T934] in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid:
934, name: kworker/1:4
[ 129.444740][ T934] preempt_count: 201, expected: 0
[ 129.444756][ T934] RCU nest depth: 0, expected: 0
[ 129.444781][ T934] Preemption disabled at:
[ 129.444789][ T934] [<ffffffd816231900>] shrink_work+0x21c/0x248
[ 129.445167][ T934] kernel BUG at kernel/sched/walt/walt_debug.c:16!
[ 129.445183][ T934] Internal error: Oops - BUG: 00000000f2000800 [#1]
PREEMPT SMP
[ 129.445204][ T934] Skip md ftrace buffer dump for: 0x1609e0
[ 129.447348][ T934] CPU: 1 PID: 934 Comm: kworker/1:4 Tainted: G W
OE 6.6.56-android15-8-o-g6f82312b30b9-debug #1
1400000003000000474e5500b3187743670464e8
[ 129.447362][ T934] Hardware name: Qualcomm Technologies, Inc. Parrot QRD,
Alpha-M (DT)
[ 129.447373][ T934] Workqueue: dm_bufio_cache shrink_work
[ 129.447394][ T934] pstate: 60400005 (nZCv daif +PAN -UAO -TCO -DIT -SSBS
BTYPE=--)
[ 129.447406][ T934] pc : android_rvh_schedule_bug+0x0/0x8 [sched_walt_debug]
[ 129.447435][ T934] lr : __traceiter_android_rvh_schedule_bug+0x44/0x6c
[ 129.447451][ T934] sp : ffffffc0843dbc90
[ 129.447459][ T934] x29: ffffffc0843dbc90 x28: ffffffffffffffff x27:
0000000000000c8b
[ 129.447479][ T934] x26: 0000000000000040 x25: ffffff804b3d6260 x24:
ffffffd816232b68
[ 129.447497][ T934] x23: ffffff805171c5b4 x22: 0000000000000000 x21:
ffffffd816231900
[ 129.447517][ T934] x20: ffffff80306ba898 x19: 0000000000000000 x18:
ffffffc084159030
[ 129.447535][ T934] x17: 00000000d2b5dd1f x16: 00000000d2b5dd1f x15:
ffffffd816720358
[ 129.447554][ T934] x14: 0000000000000004 x13: ffffff89ef978000 x12:
0000000000000003
[ 129.447572][ T934] x11: ffffffd817a823c4 x10: 0000000000000202 x9 :
7e779c5735de9400
[ 129.447591][ T934] x8 : ffffffd81560d004 x7 : 205b5d3938373434 x6 :
ffffffd8167397c8
[ 129.447610][ T934] x5 : 0000000000000000 x4 : 0000000000000001 x3 :
ffffffc0843db9e0
[ 129.447629][ T934] x2 : 0000000000002f15 x1 : 0000000000000000 x0 :
0000000000000000
[ 129.447647][ T934] Call trace:
[ 129.447655][ T934] android_rvh_schedule_bug+0x0/0x8 [sched_walt_debug
1400000003000000474e550080cce8a8a78606b6]
[ 129.447681][ T934] __might_resched+0x190/0x1a8
[ 129.447694][ T934] shrink_work+0x180/0x248
[ 129.447706][ T934] process_one_work+0x260/0x624
[ 129.447718][ T934] worker_thread+0x28c/0x454
[ 129.447729][ T934] kthread+0x118/0x158
[ 129.447742][ T934] ret_from_fork+0x10/0x20
[ 129.447761][ T934] Code: ???????? ???????? ???????? d2b5dd1f (d4210000)
[ 129.447772][ T934] ---[ end trace 0000000000000000 ]---
dm_bufio_lock will call spin_lock_bh when try_verify_in_tasklet
is enabled, and __scan will be called in atomic context.
Signed-off-by: LongPing Wei <weilongp...@oppo.com>
Cc: sta...@vger.kernel.org
---
drivers/md/dm-bufio.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
Index: linux-2.6/drivers/md/dm-bufio.c
===================================================================
--- linux-2.6.orig/drivers/md/dm-bufio.c 2025-04-14 16:01:58.000000000
+0200
+++ linux-2.6/drivers/md/dm-bufio.c 2025-04-16 14:18:44.000000000 +0200
@@ -2424,7 +2424,12 @@ static void __scan(struct dm_bufio_clien
atomic_long_dec(&c->need_shrink);
freed++;
- cond_resched();
+
+ if (!(freed & 15)) {
+ dm_bufio_unlock(c);
+ cond_resched();
+ dm_bufio_lock(c);
+ }
}
}
}
Hi, Mikulas
I have tested my v2 patch with try_verify_in_tasklet enabled on my
device and the BUG is fixed.
Should we change the current behaviour for devices wihtout
try_verify_in_tasklet enabled?
Thanks
LongPing
