Date: Tue, 10 Mar 2020 11:06:57 +0100 From: Szabolcs Nagy <nsz@...t70.net> To: Pirmin Walthert <pirmin.walthert@...om.ch> Cc: musl@...ts.openwall.com Subject: Re: Re: FYI: some observations when testing next-gen malloc * Pirmin Walthert <pirmin.walthert@...om.ch> [2020-03-10 10:44:46 +0100]: > Am 09.03.20 um 19:55 schrieb Szabolcs Nagy: > > * Pirmin Walthert <pirmin.walthert@...om.ch> [2020-03-09 19:14:59 +0100]: > > > Am 09.03.20 um 18:12 schrieb Rich Felker: > > > > It's not described very rigorously, but effectively it's in an async > > > > signal context and can only call functions which are AS-safe. > > > > > > > > A future version of the standard is expected to drop the requirement > > > > that fork itself be async-signal-safe, and may thereby add > > > > requirements to synchronize against some or all internal locks so that > > > > the child can inherit a working context. But the right solution here is > > > > always to stop using fork without exec. > > > > > > > > Rich > > > Well, I have now changed the code a bit to make sure that no > > > async-signal-unsafe command is being executed before execl. Things I've > > > removed: > > > > > > a call to cap_from_text, cap_set_proc and cap_free has been removed as well > > > as sched_setscheduler. Now the only thing being executed before execl in the > > > child process is closefrom() > > > > closefrom is not as-safe. > > > > i think it reads /proc/self/fd directory to close fds. > > (haven't checked the specific asterisk version) > > opendir calls malloc so it can deadlock. > > > Indeed I am not able to reproduce the problem any longer with a modified > version of asterisk. What I've changed is: > > Removed some code that sets the capabilities after fork() (with > cap_from_text, cap_set_proc, cap_free) and closefrom replaced with a thumb > loop over all possible fds up to sysconf(_SC_OPEN_MAX). With this > modification the fd closing procedure with max open files set to 21471 now > needs 7ms instead of 70ns (so a slowdown by times 100), however this is not > critical in our environment... > > Will discuss the findings with the asterisk developers. > > Thanks for your hints! good. ideally they would use close-on-exec fds and then you don't need such ugliness. please don't drop the list from replies.
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