Date: Wed, 5 Dec 2018 22:17:56 -0500 From: Rich Felker <dalias@...c.org> To: musl@...ts.openwall.com Subject: Re: sem_wait and EINTR On Thu, Dec 06, 2018 at 02:43:40AM +0000, Orivej Desh wrote: > * Rich Felker <dalias@...c.org> [2018-12-05] > > On Wed, Dec 05, 2018 at 10:27:16PM +0100, Ondřej Jirman wrote: > > > On Wed, Dec 05, 2018 at 08:47:59PM +0100, Markus Wichmann wrote: > > > > > > It's specified by POSIX: > > > > > > https://pubs.opengroup.org/onlinepubs/9699919799/functions/sem_wait.html > > > > > > Sates: "The sem_wait() function is interruptible by the delivery of a signal." > > > > This seems contradictory with EINTR being a "may fail" error, and, if > > interpreted the way you want to interpret it, seems to be > > contradictory with SA_RESTART semantics, since it doesn't say anything > > about whether that signal is an interrupting one. I think we should > > attempt to obtain a clarification on what the intent is here. Does "is > > interruptible" mean that it needs to fail on signals (only without > > SA_RESTART?) or simply that signal handlers must be permitted to run > > (i.e. the wait can't happen with signals blocked)? > > There is a definition of interruptible functions on the sigaction page: > > SA_RESTART > > This flag affects the behavior of interruptible functions; that is, those > specified to fail with errno set to [EINTR]. > > If set, and a function specified as interruptible is interrupted by this > signal, the function shall restart and shall not fail with [EINTR] unless > otherwise specified. > > If the flag is not set, interruptible functions interrupted by this signal > shall fail with errno set to [EINTR]. > > https://pubs.opengroup.org/onlinepubs/9699919799/functions/sigaction.html OK, this seems correct. I still don't understand why EINTR is a "may fail" error; it's been that way at least back to SUSv2: http://pubs.opengroup.org/onlinepubs/7908799/xsh/sem_wait.html I'd like it if we could avoid the pre-linux-2.6.22 bug of spurious EINTR from SYS_futex, but I don't see any way to do so except possibly wrapping all signal handlers and implementing restart-vs-EINTR ourselves. So if we need to change this, it might just be a case where we say "well, sorry, your kernel is broken" if someone is using a broken kernel. Thoughts? Rich
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