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Following test can cause IO hang:
mdadm -CvR /dev/md0 -l10 -n4 /dev/sd[abcd] --assume-clean --chunk=64K --bitmap=none
sleep 5
echo 1 > /sys/block/sda/device/delete
echo 1 > /sys/block/sdb/device/delete
echo 1 > /sys/block/sdc/device/delete
echo 1 > /sys/block/sdd/device/delete
dd if=/dev/md0 of=/dev/null bs=8k count=1 iflag=direct
Root cause:
1) all disks removed, however all rdevs in the array is still in sync,
IO will be issued normally.
2) IO failure from sda, and set badblocks failed, sda will be faulty
and MD_SB_CHANGING_PENDING will be set.
3) error recovery try to recover this IO from other disks, IO will be
issued to sdb, sdc, and sdd.
4) IO failure from sdb, and set badblocks failed again, now array is
broken and will become read-only.
5) IO failure from sdc and sdd, however, stripe can't be handled anymore
because MD_SB_CHANGING_PENDING is set:
handle_stripe
handle_stripe
if (test_bit MD_SB_CHANGING_PENDING)
set_bit STRIPE_HANDLE
goto finish
// skip handling failed stripe
release_stripe
if (test_bit STRIPE_HANDLE)
list_add_tail conf->hand_list
6) later raid5d can't handle failed stripe as well:
raid5d
md_check_recovery
md_update_sb
if (!md_is_rdwr())
// can't clear pending bit
return
if (test_bit MD_SB_CHANGING_PENDING)
break;
// can't handle failed stripe
Since MD_SB_CHANGING_PENDING can never be cleared for read-only array,
fix this problem by skip this checking for read-only array.
Link: https://lore.kernel.org/linux-raid/20251117085557.770572-3-yukuai@fnnas.com
Fixes: d87f064f58 ("md: never update metadata when array is read-only.")
Signed-off-by: Yu Kuai <yukuai@fnnas.com>
Reviewed-by: Li Nan <linan122@huawei.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.