This is the warning trigger line:
int bch_cached_dev_writeback_start(struct cached_dev *dc)
...
WARN_ON(test_and_set_bit(BCACHE_DEV_WB_RUNNING, &dc->disk.flags));
...
This commit fixes this problem:
commit 1f0ffa67349c56ea54c03ccfd1e073c990e7411e
Author: Coly Li <[email protected]>
Date: Mon Jun 10 06:13:35 2019 +0800
bcache: only set BCACHE_DEV_WB_RUNNING when cached device
attached
It is included in linux 5.2, so for now only Ubuntu Eoan has the fix;
I could reproduce the problem with Ubuntu Disco (5.0-based) kernel.
The problem can Oops the kernel (worse error) if the cache is not
attached soon (reproduced below).
I'll provide a test kernel with the fix soon.
Steps to reproduce:
------------------
With attach (last line in script):
$ sudo ./setup-bcache-wb_percent-before-attach.sh
...
[ 36.130659] WARNING: CPU: 2 PID: 1288 at
drivers/md/bcache/writeback.c:837 bch_cached_dev_writeback_start+0x156/0x164
[bcache]
...
[ 36.155742] RIP: 0010:bch_cached_dev_writeback_start+0x156/0x164 [bcache]
...
[ 36.182455] Call Trace:
[ 36.183387] bch_cached_dev_attach+0x356/0x480 [bcache]
[ 36.185104] ? bch_keybuf_init+0x70/0x70 [bcache]
[ 36.186653] __cached_dev_store+0x59f/0x8b0 [bcache]
[ 36.188274] bch_cached_dev_store+0x39/0xc0 [bcache]
[ 36.189887] sysfs_kf_write+0x3b/0x40
[ 36.191142] kernfs_fop_write+0x12e/0x1b0
[ 36.192502] __vfs_write+0x1b/0x40
[ 36.193686] vfs_write+0xab/0x1b0
[ 36.194842] ksys_write+0x5c/0xd0
[ 36.196026] __x64_sys_write+0x1a/0x20
[ 36.197296] do_syscall_64+0x5a/0x110
[ 36.198532] entry_SYSCALL_64_after_hwframe+0x44/0xa9
[ 36.200158] RIP: 0033:0x7f69a1d09154
...
[ 36.222967] ---[ end trace ec65e906cd03afa6 ]---
[ 36.225017] bcache: bch_cached_dev_attach() Caching loop0 as bcache0 on
set 57322d7a-1421-4dfc-a8cb-9c7b4e60c50a
Without attach (last line in script):
in a few seconds:
$ sudo ./setup-bcache-wb_percent-before-attach.sh
...
[ 30.623677] BUG: unable to handle kernel NULL pointer dereference at
0000000000000340
[ 30.627527] #PF error: [normal kernel read fault]
[ 30.629825] PGD 0 P4D 0
[ 30.631194] Oops: 0000 [#1] SMP PTI
...
[ 30.638818] Workqueue: events update_writeback_rate [bcache]
[ 30.640543] RIP: 0010:update_writeback_rate+0x36/0x330 [bcache]
...
[ 30.668496] Call Trace:
[ 30.670003] ? __schedule+0x2d8/0x840
[ 30.671998] process_one_work+0x20f/0x410
[ 30.674163] worker_thread+0x34/0x400
[ 30.676160] kthread+0x120/0x140
[ 30.678014] ? process_one_work+0x410/0x410
[ 30.680238] ? __kthread_parkme+0x70/0x70
[ 30.682411] ret_from_fork+0x35/0x40
...
[ 30.704646] ---[ end trace 1bbc1b34c704f1c5 ]---
[ 30.707086] RIP: 0010:update_writeback_rate+0x36/0x330 [bcache]
Test script:
$ cat setup-bcache-wb_percent-before-attach.sh
#!/bin/sh
#set -ex
dmesg -C
echo 9 > /proc/sys/kernel/printk
FILE_BACKING=/backing.img
FILE_CACHING=/caching.img
dd if=/dev/zero of=$FILE_BACKING bs=1G seek=1 count=0
dd if=/dev/zero of=$FILE_CACHING bs=1G seek=1 count=0
dd if=/dev/zero of=$FILE_BACKING bs=1M count=1 conv=notrunc
dd if=/dev/zero of=$FILE_CACHING bs=1M count=1 conv=notrunc
LOOP_BACKING=$(losetup -f --show $FILE_BACKING)
LOOP_CACHING=$(losetup -f --show $FILE_CACHING)
make-bcache -B $LOOP_BACKING
make-bcache -C $LOOP_CACHING
sleep 3
CSET_UUID=$(bcache-super-show $LOOP_CACHING | awk '/cset\.uuid/ { print
$2 }')
# Change writeback_percent before attaching
echo 11 > /sys/block/$(basename $LOOP_BACKING)/bcache/writeback_percent
sleep 1
# Comment this line to Oops in a few seconds
echo $CSET_UUID > /sys/block/$(basename $LOOP_BACKING)/bcache/attach
--
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https://bugs.launchpad.net/bugs/1837788
Title:
bcache kernel warning when attaching device
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