linux-kernel - Re: [PATCH v2 4/5] exec: Move exec_mmap right after de_thread in flush_old

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Message-ID: <87sgihxo4h.fsf@x220.int.ebiederm.org>
Date:   Mon, 09 Mar 2020 15:35:42 -0500
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     Bernd Edlinger <bernd.edlinger@...mail.de>
Cc:     Christian Brauner <christian.brauner@...ntu.com>,
        Kees Cook <keescook@...omium.org>,
        Jann Horn <jannh@...gle.com>, Jonathan Corbet <corbet@....net>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Oleg Nesterov <oleg@...hat.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Andrei Vagin <avagin@...il.com>,
        Ingo Molnar <mingo@...nel.org>,
        "Peter Zijlstra \(Intel\)" <peterz@...radead.org>,
        Yuyang Du <duyuyang@...il.com>,
        David Hildenbrand <david@...hat.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Anshuman Khandual <anshuman.khandual@....com>,
        David Howells <dhowells@...hat.com>,
        James Morris <jamorris@...ux.microsoft.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Shakeel Butt <shakeelb@...gle.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Christian Kellner <christian@...lner.me>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Aleksa Sarai <cyphar@...har.com>,
        "Dmitry V. Levin" <ldv@...linux.org>,
        "linux-doc\@vger.kernel.org" <linux-doc@...r.kernel.org>,
        "linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-fsdevel\@vger.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "linux-mm\@kvack.org" <linux-mm@...ck.org>,
        "stable\@vger.kernel.org" <stable@...r.kernel.org>,
        "linux-api\@vger.kernel.org" <linux-api@...r.kernel.org>
Subject: Re: [PATCH v2 4/5] exec: Move exec_mmap right after de_thread in flush_old_exec

Bernd Edlinger <bernd.edlinger@...mail.de> writes:

> On 3/9/20 8:58 PM, Eric W. Biederman wrote:
>> 
>> Ok.  I think this has it sorted:
>> 
>>     exec: Move exec_mmap right after de_thread in flush_old_exec
>>     
>>     I have read through the code in exec_mmap and I do not see anything
>>     that depends on sighand or the sighand lock, or on signals in anyway
>>     so this should be safe.
>>     
>>     This rearrangement of code has two significant benefits.  It makes
>>     the determination of passing the point of no return by testing bprm->mm
>>     accurate.  All failures prior to that point in flush_old_exec are
>>     either truly recoverable or they are fatal.
>>     
>>     Further this consolidates all of the possible indefinite waits for
>>     userspace together at the top of flush_old_exec.  The possible wait
>>     for a ptracer on PTRACE_EVENT_EXIT, the possible wait for a page fault
>>     to be resolved in clear_child_tid, and the possible wait for a page
>>     fault in exit_robust_list.
>>     
>>     This consolidation allows the creation of a mutex to replace
>>     cred_guard_mutex that is not held over possible indefinite userspace
>>     waits.  Which will allow removing deadlock scenarios from the kernel.
>>     
>>     Reviewed-by: Bernd Edlinger <bernd.edlinger@...mail.de>
>>     Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
>> 
>> 
>> I don't think I usually have this many typos.  Sigh.
>> 
>
> OK.
>
> never mind,

No no.  I really appreciate all of the scrutiny.  Frequently the issues
that will produce typos or poor patch descriptions are also the issues
that will produce sloppy patches as well.  I was just frustrated with
myself.

Eric