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From:   ebiederm@xmission.com (Eric W. Biederman)
To:     Jens Axboe <axboe@kernel.dk>
Cc:     Al Viro <viro@zeniv.linux.org.uk>, Qian Cai <cai@redhat.com>,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
References: <20201030152407.43598-1-cai@redhat.com>
        <20201030184255.GP3576660@ZenIV.linux.org.uk>
        <ad9357e9-8364-a316-392d-7504af614cac@kernel.dk>
        <20201030184918.GQ3576660@ZenIV.linux.org.uk>
        <d858ba48-624f-43be-93cf-07d94f0ebefd@kernel.dk>
        <20201030222213.GR3576660@ZenIV.linux.org.uk>
        <a1e17902-a204-f03d-2a51-469633eca751@kernel.dk>
Date:   Mon, 02 Nov 2020 13:27:17 -0600
In-Reply-To: <a1e17902-a204-f03d-2a51-469633eca751@kernel.dk> (Jens Axboe's
        message of "Fri, 30 Oct 2020 17:21:39 -0600")
Message-ID: <87eelba7ai.fsf@x220.int.ebiederm.org>
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Subject: Re: [PATCH -next] fs: Fix memory leaks in do_renameat2() error paths
Precedence: bulk

Jens Axboe <axboe@kernel.dk> writes:

> On 10/30/20 4:22 PM, Al Viro wrote:
>> On Fri, Oct 30, 2020 at 02:33:11PM -0600, Jens Axboe wrote:
>>> On 10/30/20 12:49 PM, Al Viro wrote:
>>>> On Fri, Oct 30, 2020 at 12:46:26PM -0600, Jens Axboe wrote:
>>>>
>>>>> See other reply, it's being posted soon, just haven't gotten there yet
>>>>> and it wasn't ready.
>>>>>
>>>>> It's a prep patch so we can call do_renameat2 and pass in a filename
>>>>> instead. The intent is not to have any functional changes in that prep
>>>>> patch. But once we can pass in filenames instead of user pointers, it's
>>>>> usable from io_uring.
>>>>
>>>> You do realize that pathname resolution is *NOT* offloadable to helper
>>>> threads, I hope...
>>>
>>> How so? If we have all the necessary context assigned, what's preventing
>>> it from working?
>> 
>> Semantics of /proc/self/..., for starters (and things like /proc/mounts, etc.
>> *do* pass through that, /dev/stdin included)
>
> Don't we just need ->thread_pid for that to work?

No.  You need ->signal.

You need ->signal->pids[PIDTYPE_TGID].  It is only for /proc/thread-self
that ->thread_pid is needed.

Even more so than ->thread_pid, it is a kernel invariant that ->signal
does not change.

Eric