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Message-ID: <bug-219166-13602-CwLQ6nAqGv@https.bugzilla.kernel.org/>
Date: Thu, 05 Sep 2024 09:32:51 +0000
From: bugzilla-daemon@...nel.org
To: linux-ext4@...r.kernel.org
Subject: [Bug 219166] occasional block layer hang when setting 'echo noop >
/sys/block/sda/queue/scheduler'
https://bugzilla.kernel.org/show_bug.cgi?id=219166
--- Comment #13 from Richard W.M. Jones (rjones@...hat.com) ---
To document for myself and others what I did to reproduce the bug and get the
kernel stack trace ...
(1) libguestfs from git with this patch reverted:
https://github.com/libguestfs/libguestfs/commit/b2d682a4730ead8b4ae07e5aaf6fa230c5eec305
(2) Run guestfish in a loop until it hangs:
$ while LIBGUESTFS_BACKEND_SETTINGS=force_tcg ./run guestfish -a /dev/null run
-vx >& /tmp/log ; do echo -n . ; done
(3) Looking /tmp/log we can see it hung just after trying to set noop
scheduler:
$ tail -5 /tmp/log
+ echo 300
+ for f in /sys/block/sd*/device/timeout
+ echo 300
+ for f in /sys/block/{h,s,ub,v}d*/queue/scheduler
+ echo noop
(4) Check the log for the kernel version, install the corresponding kernel
debuginfo.
(5) Get virsh to produce a core dump of the VM:
$ virsh list
Id Name State
--------------------------------------------
1950 guestfs-lsdbxy71u4jg1w6x running
$ virsh dump 1950 /var/tmp/core --memory-only
Domain '1950' dumped to /var/tmp/core
(6) Open in 'crash':
$ crash
/usr/lib/debug/lib/modules/6.11.0-0.rc5.20240830git20371ba12063.47.fc42.x86_64/vmlinux
/var/tmp/core
(7) List processes and find the one which hung:
crash> ps
...
230 73 0 ffffa01f83c58000 UN 0.3 11608 3340 modprobe
(8) Get stack trace from the hung process:
crash> set 230
PID: 230
COMMAND: "modprobe"
TASK: ffffa01f83c58000 [THREAD_INFO: ffffa01f83c58000]
CPU: 0
STATE: TASK_UNINTERRUPTIBLE
crash> bt
PID: 230 TASK: ffffa01f83c58000 CPU: 0 COMMAND: "modprobe"
#0 [ffffc1db0030f840] __schedule at ffffffff921906d0
#1 [ffffc1db0030f8f8] schedule at ffffffff92191a27
#2 [ffffc1db0030f908] __bio_queue_enter at ffffffff917e17dc
#3 [ffffc1db0030f968] blk_mq_submit_bio at ffffffff917f3b4c
#4 [ffffc1db0030f9f0] __submit_bio at ffffffff917e23fc
#5 [ffffc1db0030fa58] submit_bio_noacct_nocheck at ffffffff917e28e6
#6 [ffffc1db0030fac0] ext4_mpage_readpages at ffffffff915cef7c
#7 [ffffc1db0030fbe0] read_pages at ffffffff91381cda
#8 [ffffc1db0030fc40] page_cache_ra_unbounded at ffffffff91381fb5
#9 [ffffc1db0030fca8] filemap_fault at ffffffff91376175
#10 [ffffc1db0030fd48] __do_fault at ffffffff913d1755
#11 [ffffc1db0030fd70] do_fault at ffffffff913d22e5
#12 [ffffc1db0030fda0] __handle_mm_fault at ffffffff913d8b2b
#13 [ffffc1db0030fe88] handle_mm_fault at ffffffff913d9472
#14 [ffffc1db0030fec8] do_user_addr_fault at ffffffff910b34ea
#15 [ffffc1db0030ff28] exc_page_fault at ffffffff92187e4e
#16 [ffffc1db0030ff50] asm_exc_page_fault at ffffffff922012a6
RIP: 000055bb085508d8 RSP: 00007ffc3e731900 RFLAGS: 00010206
RAX: 00000000000becd6 RBX: 00007f39925d1cd6 RCX: 000055bb0856592a
RDX: 00007ffc3e733c70 RSI: 00000000200becd6 RDI: 000055bb1a712970
RBP: 00007ffc3e731b60 R8: 0000000000000000 R9: 0000000000000000
R10: 0000000000000000 R11: 0000000000000202 R12: 00000000200becd6
R13: 000055bb1a712970 R14: 00007ffc3e733c70 R15: 000055bb0856a708
ORIG_RAX: ffffffffffffffff CS: 0033 SS: 002b
--
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