From mboxrd@z Thu Jan 1 00:00:00 1970 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on inbox.vuxu.org X-Spam-Level: X-Spam-Status: No, score=-3.3 required=5.0 tests=MAILING_LIST_MULTI, RCVD_IN_DNSWL_MED,RCVD_IN_MSPIKE_H3,RCVD_IN_MSPIKE_WL autolearn=ham autolearn_force=no version=3.4.4 Received: (qmail 1490 invoked from network); 15 Oct 2020 17:13:31 -0000 Received: from mother.openwall.net (195.42.179.200) by inbox.vuxu.org with ESMTPUTF8; 15 Oct 2020 17:13:31 -0000 Received: (qmail 29910 invoked by uid 550); 15 Oct 2020 17:13:29 -0000 Mailing-List: contact musl-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Reply-To: musl@lists.openwall.com Received: (qmail 29892 invoked from network); 15 Oct 2020 17:13:28 -0000 Date: Thu, 15 Oct 2020 13:13:16 -0400 From: Rich Felker To: Alexey Izbyshev Cc: musl@lists.openwall.com Message-ID: <20201015171315.GV17637@brightrain.aerifal.cx> References: <948f6fc6f3458f18152c0f8b505beec0@ispras.ru> <20201015085024.GR2947641@port70.net> <20201015154925.GU17637@brightrain.aerifal.cx> <68e70f27d78c9507631dd2c22187f77d@ispras.ru> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <68e70f27d78c9507631dd2c22187f77d@ispras.ru> User-Agent: Mutt/1.5.21 (2010-09-15) Subject: Re: [musl] Why is setrlimit() considered to have per-thread effect? On Thu, Oct 15, 2020 at 07:13:30PM +0300, Alexey Izbyshev wrote: > On 2020-10-15 18:49, Rich Felker wrote: > >setrlimit implemented in terms of prlimit does; as far as I can tell > >prlimit does not perform any process-global action itself but just > >lets you target different tasks. This means we *could* "optimize" > >setrlimit to skip __synccall and instead just iterate over the thread > >list and SYS_prlimit each one from the calling thread context. > > > >The prlimit function on the other hand behaves as the Linux syscall > >and lets you set thread-specific limits. > > > But in my understanding, prlimit() sets process- (not thread-) > specific limits, and have done so since its introduction[1]. The That was not my understanding, but it may be true. I would not assume it's true just because of the word "process" in a commit message or comment since kernel folks, especially in that era, regularly used "process" and "thread" interchangibly/inconsistently. > code operates on "signal" structure which is shared between threads > of a thread group. Further, an earlier commit[2] explicitly says > that "...rlimit are > per process and not per-thread.". It's true that in pre-2.6.10 > kernels setrlimit() operated in per-thread limits (see my reply to > Szabolcs), but it's not related to prlimit() syscall, which was > added much later. > > To be clear, I did not propose to optimize setrlimit() in my initial > email, I was just surprised that synccall() is needed at all. But if > we want optimization, it seems that trying prlimit() first and > falling back to synccall() in case of ENOSYS would be what we want. If correct, I agree -- we can avoid the need for __synccall when prlimit works. I'd like to find commits or source lines supporting that in their actual (code) content though rather than just as a mention in commit messages, since it's contrary to what my (probably outdated) understanding of how rlimits worked was. > [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=c022a0acad534fd5f5d5f17280f6d4d135e74e81 > [2] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=7855c35da7ba16b389d17710401c4a55a3ea2102 Somewhat off-topic, but for some reason that second link is bringing my browser to a crawl swapping, despite the commit being tiny when I view it locally in my kernel tree. Weird. Rich