Re: NULL pointer dereference in blk_queue_flag_set

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Hey Song,

thanks for the quick reply! I applied your patch on top of 5.17-rc2 and it fixes the issue:

[   15.394670] device-mapper: raid: Loading target version 1.15.1
[   15.395216] device-mapper: raid: Ignoring chunk size parameter for RAID 1
[   15.395224] device-mapper: raid: Choosing default region size of 4MiB
[   15.399865] md/raid1:mdX: active with 2 out of 2 mirrors

Best Regards,

Leon

On 02.02.22 07:57, Song Liu wrote:
Hi Leon,

On Tue, Feb 1, 2022 at 2:15 PM jkhsjdhjs <jkhsjdhjs@xxxxxxxxxxx> wrote:
Dear Song Liu,

my kernel (5.17-rc2) experiences a NULL pointer dereference when
activating an LDM (Windows Logical Disk Manager) on Arch Linux using
ldmtool [1]. I have attached the relevant excerpt of dmesg. This bug
causes my LDM RAID to fail activating (see ldmtool-status.txt and
lsblk.txt). Since this worked fine with 5.16 I bisected the kernel and
found, that commit f51d46d0e7cb5b8494aa534d276a9d8915a2443d [2]
introduced the issue.

I'm not sure what else to add, if there's more information I can
provide, please tell me. Otherwise I'll happily assist in fixing this
issue - if there's something I can do.
Thanks for the report! And sorry for the bug.

For the next step, could you please test whether the following change
fixes the issue?

Best,
Song

diff --git i/drivers/md/md.c w/drivers/md/md.c
index 854cbf4234aa..18e987c644c6 100644
--- i/drivers/md/md.c
+++ w/drivers/md/md.c
@@ -5868,10 +5868,6 @@ int md_run(struct mddev *mddev)
                 nowait = nowait && blk_queue_nowait(bdev_get_queue(rdev->bdev));
         }

-       /* Set the NOWAIT flags if all underlying devices support it */
-       if (nowait)
-               blk_queue_flag_set(QUEUE_FLAG_NOWAIT, mddev->queue);
-
         if (!bioset_initialized(&mddev->bio_set)) {
                 err = bioset_init(&mddev->bio_set, BIO_POOL_SIZE, 0,
BIOSET_NEED_BVECS);
                 if (err)
@@ -6009,6 +6005,10 @@ int md_run(struct mddev *mddev)
                 else
                         blk_queue_flag_clear(QUEUE_FLAG_NONROT, mddev->queue);
                 blk_queue_flag_set(QUEUE_FLAG_IO_STAT, mddev->queue);
+
+               /* Set the NOWAIT flags if all underlying devices support it */
+               if (nowait)
+                       blk_queue_flag_set(QUEUE_FLAG_NOWAIT, mddev->queue);
         }
         if (pers->sync_request) {
                 if (mddev->kobj.sd &&



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