Date: Thu, 15 Oct 2020 21:26:33 +0300 From: Alexey Izbyshev <izbyshev@...ras.ru> To: musl@...ts.openwall.com Subject: Re: Why is setrlimit() considered to have per-thread effect? On 2020-10-15 20:13, Rich Felker wrote: > On Thu, Oct 15, 2020 at 07:13:30PM +0300, Alexey Izbyshev wrote: > 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 outdated) understanding of how rlimits worked was. > Here they are (the first two were referenced in my reply to Szabolcs). * Change of setrlimit() to operate on signal_struct in 2.6.10: https://elixir.bootlin.com/linux/v2.6.10/source/kernel/sys.c#L1487 (compare with https://elixir.bootlin.com/linux/v2.6.9/source/kernel/sys.c#L1537) * Definition of signal_struct in 2.6.10, which is per-thread-group (apart from "rlim", it contains many other thread-group-related fields): https://elixir.bootlin.com/linux/v2.6.10/source/include/linux/sched.h#L268 * Usage if signal_struct in 2.6.36 (the first kernel with prlimit()) in do_prlimit(), which is a common function implementing setrlimit(), getrlimit() and prlimit(): https://elixir.bootlin.com/linux/v2.6.36/source/kernel/sys.c#L1333 Finally, I performed a simple experiment: on 2.6.30 kernel (with glibc 2.5), created a thread and changed RLIMIT_FSIZE via setrlimit(). After that, "/proc/pid/limits" reported the new limit, so it was applied to the whole process. Strace confirmed that only a single setrlimit() system call was performed.
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