On 2019/6/4 10:59 下午, Coly Li wrote: > On 2019/6/4 7:00 下午, Bjørn Forsman wrote: >> Hi all, >> >> I get a kernel oops from bcache when writing to >> /sys/block/bcache0/bcache/writeback_percent and there is no attached >> cache device. See the oops itself below my signature. >> >> This is on Linux 4.19.46. I looked in git and see many commits to >> bcache lately, but none seem to address this particular issue. >> >> Background: I'm writing to .../writeback_percent with >> systemd-tmpfiles. I'd rather not replace it with a script that figures >> out whether or not the kernel will oops if writing to the sysfs file >> -- the kernel should not oops in the first place. > > Hi Bjorn, > > Thank you for the reporting. I believe this is a case we missed in > testings. When a bcache device is not attached, it does not make sense > to update the writeback rate in period by the changing of writeback_percent. > > I will post a patch for your testing soon. Hi Bjorn, Could you please to try this patch ? Hope it may help a bit. Thanks. Coly Li >> >> Jun 04 12:35:42 kernel: BUG: unable to handle kernel NULL pointer >> dereference at 0000000000000340 >> Jun 04 12:35:42 kernel: PGD 0 P4D 0 >> Jun 04 12:35:42 kernel: Oops: 0000 [#1] SMP PTI >> Jun 04 12:35:42 kernel: CPU: 6 PID: 20266 Comm: kworker/6:220 Not >> tainted 4.19.46 #1-NixOS >> Jun 04 12:35:42 kernel: Hardware name: To Be Filled By O.E.M. To Be >> Filled By O.E.M./X99 Extreme4/3.1, BIOS P3.60 04/06/2018 >> Jun 04 12:35:42 kernel: Workqueue: events update_writeback_rate [bcache] >> Jun 04 12:35:42 kernel: RIP: 0010:update_writeback_rate+0x2f/0x2e0 [bcache] [snipped]
From 9dea1e6ad0e6c40e3bc6ee6cf4ad243c07ca6ca9 Mon Sep 17 00:00:00 2001 From: Coly Li <colyli@xxxxxxx> Date: Tue, 4 Jun 2019 23:24:09 +0800 Subject: [PATCH] bcache: only set BCACHE_DEV_WB_RUNNING when cached device attached When people set a writeback percent via sysfs file, /sys/block/bcache<N>/bcache/writeback_percent current code directly sets BCACHE_DEV_WB_RUNNING to dc->disk.flags and schedules kworker dc->writeback_rate_update. If there is no cache set attached to, the writebac kernel thread is not running indeed, running dc->writeback_rate_update does not make sense and may cause NULL pointer deference when reference cache set pointer inside update_writeback_rate(). This patch checks whether the cache set point (dc->disk.c) is NULL in sysfs interface handler, and only set BCACHE_DEV_WB_RUNNING and schedule dc->writeback_rate_update when dc->disk.c is not NULL (it means the cache device is attached to a cache set). Reported-by: Bjørn Forsman <bjorn.forsman@xxxxxxxxx> Signed-off-by: Coly Li <colyli@xxxxxxx> --- drivers/md/bcache/sysfs.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/drivers/md/bcache/sysfs.c b/drivers/md/bcache/sysfs.c index 129031663cc8..eb678e43ac00 100644 --- a/drivers/md/bcache/sysfs.c +++ b/drivers/md/bcache/sysfs.c @@ -430,8 +430,13 @@ STORE(bch_cached_dev) bch_writeback_queue(dc); } + /* + * Only set BCACHE_DEV_WB_RUNNING when cached device attached to + * a cache set, otherwise it doesn't make sense. + */ if (attr == &sysfs_writeback_percent) - if (!test_and_set_bit(BCACHE_DEV_WB_RUNNING, &dc->disk.flags)) + if ((dc->disk.c != NULL) && + (!test_and_set_bit(BCACHE_DEV_WB_RUNNING, &dc->disk.flags))) schedule_delayed_work(&dc->writeback_rate_update, dc->writeback_rate_update_seconds * HZ); -- 2.16.4
