From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
To: Linus Torvalds <torvalds@linux-foundation.org>,
Hillf Danton <hdanton@sina.com>
Cc: syzbot <syzbot+83e7f982ca045ab4405c@syzkaller.appspotmail.com>,
andrii@kernel.org, bpf@vger.kernel.org,
linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com
Subject: Re: [syzbot] [bpf?] [trace?] possible deadlock in force_sig_info_to_task
Date: Mon, 29 Apr 2024 10:00:30 +0900 [thread overview]
Message-ID: <a93a0b0f-4607-46d6-937d-0ddf3544bb2d@I-love.SAKURA.ne.jp> (raw)
In-Reply-To: <CAHk-=wjma_sSghVTgDCQxHHd=e2Lqi45PLh78oJ4WeBj8erV9Q@mail.gmail.com>
On 2024/04/29 9:50, Linus Torvalds wrote:
> On Sun, 28 Apr 2024 at 16:23, Hillf Danton <hdanton@sina.com> wrote:
>>
>> So is game like copying from/putting to user with runqueue locked
>> at the first place.
>
> No, that should be perfectly fine. In fact, it's even normal. It would
> happen any time you have any kind of tracing thing, where looking up
> the user mode frame involves doing user accesses with page faults
> disabled.
>
> The runqueue lock is irrelevant. As mentioned, it's only a symptom of
> something else going wrong.
>
> Now, judging by the syz reproducer, the trigger for this all is almost
> certainly that
>
> bpf$BPF_RAW_TRACEPOINT_OPEN(0x11,
> &(0x7f00000000c0)={&(0x7f0000000080)='sched_switch\x00', r0}, 0x10)
>
> and that probably causes the instability. But the immediate problem is
> not the user space access, it's that something goes horribly wrong
> *around* it.
I can't recall title of the commit, but I feel that things went very wrong
after a commit that allows running tracing function upon lock contention
(run code when e.g. a spinlock could not be taken) was introduced.
That commit is forming random locking dependency, resulting in flood of
lockdep warnings.
>
>> Plus as per another syzbot report [1], bpf could make trouble with
>> workqueue pool locked.
>
> That seems to be entirely different. There's no unexplained page fault
> in that case, that seems to be purely a "take lock in the wrong order"
>
> Linus
next prev parent reply other threads:[~2024-04-29 1:00 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-25 9:05 [syzbot] [bpf?] [trace?] possible deadlock in force_sig_info_to_task syzbot
2024-04-25 17:54 ` Jiri Olsa
2024-04-27 20:00 ` syzbot
2024-04-27 23:13 ` Hillf Danton
2024-04-28 20:01 ` Linus Torvalds
2024-04-28 20:22 ` Linus Torvalds
2024-04-28 23:23 ` Hillf Danton
2024-04-29 0:50 ` Linus Torvalds
2024-04-29 1:00 ` Tetsuo Handa [this message]
2024-04-29 1:33 ` Linus Torvalds
2024-04-29 8:00 ` [PATCH] x86/mm: Remove broken vsyscall emulation code from the page fault code Ingo Molnar
2024-04-29 13:51 ` Jiri Olsa
2024-04-29 23:30 ` Andy Lutomirski
2024-04-29 15:51 ` Linus Torvalds
2024-04-29 18:47 ` Linus Torvalds
2024-04-29 19:07 ` Linus Torvalds
2024-04-29 23:29 ` Andy Lutomirski
2024-04-30 0:05 ` Linus Torvalds
2024-04-30 6:10 ` Ingo Molnar
2024-05-01 7:43 ` Ingo Molnar
2024-04-30 14:53 ` kernel test robot
2024-04-29 10:39 ` [syzbot] [bpf?] [trace?] possible deadlock in force_sig_info_to_task Hillf Danton
2024-04-29 11:35 ` syzbot
2024-04-30 6:16 ` [tip: x86/urgent] x86/mm: Remove broken vsyscall emulation code from the page fault code tip-bot2 for Linus Torvalds
2024-05-01 7:50 ` tip-bot2 for Linus Torvalds
2024-04-29 14:17 ` [syzbot] [bpf?] [trace?] possible deadlock in force_sig_info_to_task Tetsuo Handa
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