linux-kernel - Re: Reminder: 22 open syzbot bugs in perf subsystem

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Date:   Wed, 3 Jul 2019 09:29:39 +0530
From:   Ravi Bangoria <ravi.bangoria@...ux.ibm.com>
To:     Eric Biggers <ebiggers@...nel.org>
Cc:     linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Song Liu <songliubraving@...com>,
        Kan Liang <kan.liang@...ux.intel.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        syzkaller-bugs@...glegroups.com, Oleg Nesterov <oleg@...hat.com>,
        Ravi Bangoria <ravi.bangoria@...ux.ibm.com>
Subject: Re: Reminder: 22 open syzbot bugs in perf subsystem

Hi Eric,

On 7/3/19 9:25 AM, Eric Biggers wrote:
> On Wed, Jul 03, 2019 at 09:09:55AM +0530, Ravi Bangoria wrote:
>>
>>
>> On 7/2/19 11:13 AM, Eric Biggers wrote:
>>> --------------------------------------------------------------------------------
>>> Title:              possible deadlock in uprobe_clear_state
>>> Last occurred:      164 days ago
>>> Reported:           201 days ago
>>> Branches:           Mainline
>>> Dashboard link:     https://syzkaller.appspot.com/bug?id=a1ce9b3da349209c5085bb8c4fee753d68c3697f
>>> Original thread:    https://lkml.kernel.org/lkml/00000000000010a9fb057cd14174@google.com/T/#u
>>>
>>> Unfortunately, this bug does not have a reproducer.
>>>
>>> No one replied to the original thread for this bug.
>>>
>>> If you fix this bug, please add the following tag to the commit:
>>>     Reported-by: syzbot+1068f09c44d151250c33@...kaller.appspotmail.com
>>>
>>> If you send any email or patch for this bug, please consider replying to the
>>> original thread.  For the git send-email command to use, or tips on how to reply
>>> if the thread isn't in your mailbox, see the "Reply instructions" at
>>> https://lkml.kernel.org/r/00000000000010a9fb057cd14174@google.com
>>>
>>
>> This is false positive:
>> https://marc.info/?l=linux-kernel&m=154925313012615&w=2
>>
> 
> What do you mean "false positive"?  Your patch says there can be a deadlock.
> Also, your patch hasn't been merged yet.  So doesn't it still need to be fixed?

Please see Oleg's reply to the patch:
https://marc.info/?l=linux-kernel&m=154946017315554&w=2

"""
But this is false positive, right? if CPU1 calls update_ref_ctr() then
either ->mm_users is already zero so binder_alloc_free_page()->mmget_not_zero()
will fail, or the caller of update_ref_ctr() has a reference and thus
binder_alloc_free_page()->mmput() can't trigger __mmput() ?
"""