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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 outdated) understanding of how rlimits worked was.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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