From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
To: Jan Kara <jack@suse.cz>
Cc: syzbot <syzbot+4a7438e774b21ddd8eca@syzkaller.appspotmail.com>,
syzkaller-bugs@googlegroups.com, linux-fsdevel@vger.kernel.org,
linux-kernel@vger.kernel.org, viro@zeniv.linux.org.uk,
axboe@kernel.dk, tj@kernel.org, david@fromorbit.com,
linux-block@vger.kernel.org
Subject: Re: general protection fault in wb_workfn (2)
Date: Thu, 31 May 2018 01:00:08 +0900 [thread overview]
Message-ID: <2dda7a11-3f6b-bdba-a68a-7c0694806cc4@I-love.SAKURA.ne.jp> (raw)
In-Reply-To: <20180528133503.awomzj6djozbo5bv@quack2.suse.cz>
So, we have no idea what is happening...
Then, what about starting from temporary debug printk() patch shown below?
>>From 4f70f72ad3c9ae6ce1678024ef740aca4958e5b0 Mon Sep 17 00:00:00 2001
From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Date: Wed, 30 May 2018 09:57:10 +0900
Subject: [PATCH] bdi: Add temporary config for debugging wb_workfn() versus
bdi_unregister() race bug.
syzbot is hitting NULL pointer dereference at wb_workfn() [1]. But due to
limitations that syzbot cannot find reproducer for this bug (frequency is
once or twice per a day) nor we can't capture vmcore in the environment
which syzbot is using, for now we need to rely on printk() debugging.
[1] https://syzkaller.appspot.com/bug?id=e0818ccb7e46190b3f1038b0c794299208ed4206
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
---
block/Kconfig | 7 +++++++
fs/fs-writeback.c | 31 +++++++++++++++++++++++++++++++
2 files changed, 38 insertions(+)
diff --git a/block/Kconfig b/block/Kconfig
index 28ec557..fbce13e 100644
--- a/block/Kconfig
+++ b/block/Kconfig
@@ -139,6 +139,13 @@ config BLK_CMDLINE_PARSER
See Documentation/block/cmdline-partition.txt for more information.
+config BLK_DEBUG_WB_WORKFN_RACE
+ bool "Dump upon hitting wb_workfn() versus bdi_unregister() race bug."
+ default n
+ ---help---
+ This is a temporary option used for obtaining information for
+ specific bug. This option will be removed after the bug is fixed.
+
config BLK_WBT
bool "Enable support for block device writeback throttling"
default n
diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 471d863..b4dd078 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -1934,6 +1934,37 @@ void wb_workfn(struct work_struct *work)
struct bdi_writeback, dwork);
long pages_written;
+#ifdef CONFIG_BLK_DEBUG_WB_WORKFN_RACE
+ if (!wb->bdi->dev) {
+ pr_warn("WARNING: %s: device is NULL\n", __func__);
+ pr_warn("wb->state=%lx\n", wb->state);
+ pr_warn("list_empty(&wb->work_list)=%u\n",
+ list_empty(&wb->work_list));
+ if (!wb->bdi)
+ pr_warn("wb->bdi == NULL\n");
+ else {
+ pr_warn("list_empty(&wb->bdi->bdi_list)=%u\n",
+ list_empty(&wb->bdi->bdi_list));
+ pr_warn("wb->bdi->wb.state=%lx\n", wb->bdi->wb.state);
+ }
+ if (!wb->congested)
+ pr_warn("wb->congested == NULL\n");
+#ifdef CONFIG_CGROUP_WRITEBACK
+ else if (!wb->congested->__bdi)
+ pr_warn("wb->congested->__bdi == NULL\n");
+ else {
+ pr_warn("(wb->congested->__bdi == wb->bdi)=%u\n",
+ wb->congested->__bdi == wb->bdi);
+ pr_warn("list_empty(&wb->congested->__bdi->bdi_list)=%u\n",
+ list_empty(&wb->congested->__bdi->bdi_list));
+ pr_warn("wb->congested->__bdi->wb.state=%lx\n",
+ wb->congested->__bdi->wb.state);
+ }
+#endif
+ /* Will halt shortly due to NULL pointer dereference... */
+ }
+#endif
+
set_worker_desc("flush-%s", dev_name(wb->bdi->dev));
current->flags |= PF_SWAPWRITE;
--
1.8.3.1
next prev parent reply other threads:[~2018-05-30 16:01 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-05-26 9:15 general protection fault in wb_workfn (2) syzbot
2018-05-27 0:47 ` Tetsuo Handa
2018-05-27 2:21 ` [PATCH] bdi: Fix another oops in wb_workfn() Tetsuo Handa
2018-05-27 2:36 ` Tejun Heo
2018-05-28 13:35 ` general protection fault in wb_workfn (2) Jan Kara
2018-05-30 16:00 ` Tetsuo Handa [this message]
2018-05-31 11:42 ` Jan Kara
2018-05-31 13:19 ` Tetsuo Handa
2018-05-31 13:42 ` Jan Kara
2018-05-31 16:56 ` Jens Axboe
2018-06-05 13:45 ` Tetsuo Handa
2018-06-07 18:46 ` Dmitry Vyukov
2018-06-08 2:31 ` Tetsuo Handa
2018-06-08 14:45 ` Dmitry Vyukov
2018-06-08 15:16 ` Dmitry Vyukov
2018-06-08 16:53 ` Dmitry Vyukov
2018-06-08 17:14 ` Dmitry Vyukov
2018-06-09 5:30 ` Tetsuo Handa
2018-06-09 14:00 ` [PATCH] bdi: Fix another oops in wb_workfn() Tetsuo Handa
2018-06-11 9:12 ` Jan Kara
2018-06-11 16:01 ` Tejun Heo
2018-06-11 16:29 ` Jan Kara
2018-06-11 17:20 ` Tejun Heo
2018-06-12 15:57 ` Jan Kara
2018-06-13 10:43 ` Tetsuo Handa
2018-06-13 11:51 ` Tetsuo Handa
2018-06-13 14:06 ` Linus Torvalds
2018-06-13 14:46 ` Jan Kara
2018-06-13 14:55 ` Linus Torvalds
2018-06-13 16:20 ` Tetsuo Handa
2018-06-13 16:25 ` Linus Torvalds
2018-06-13 16:45 ` Jan Kara
2018-06-13 21:04 ` Tetsuo Handa
2018-06-14 10:11 ` Jan Kara
2018-06-13 14:33 ` Tejun Heo
2018-06-15 12:06 ` Jan Kara
2018-06-18 12:27 ` Jan Kara
2018-06-01 2:30 ` general protection fault in wb_workfn (2) Dave Chinner
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