linux-kernel - Re: [syzbot] possible deadlock in register_for_each

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Message-ID: <20210401105305.GA18680@redhat.com>
Date:   Thu, 1 Apr 2021 12:53:26 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     Hillf Danton <hdanton@...a.com>
Cc:     Namhyung Kim <namhyung@...nel.org>,
        Song Liu <songliubraving@...com>,
        Peter Zijlstra <peterz@...radead.org>,
        syzbot <syzbot+b804f902bbb6bcf290cb@...kaller.appspotmail.com>,
        Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] possible deadlock in register_for_each_vma

On 04/01, Hillf Danton wrote:
>
> If I dont misread it,  the lockdep chain will likely evolve from
>
>    event_mutex -> uprobe.register_rwsem -> dup_mmap_sem -> mm.mmap_lock ->
>    event_mutex
> to
>    dup_mmap_sem -> mm.mmap_lock -> dup_mmap_sem
>
> after this patch as both uprobe_register() and uprobe_unregister() would take
> dup_mmap_sem.

Hmm, please correct me, but I don't think so. I think mmap_lock -> dup_mmap_sem
is not possible.

Oleg.