Messages in this thread |  | | Date | Thu, 16 Nov 2017 18:49:49 +0000 (UTC) | From | Mathieu Desnoyers <> | Subject | Re: [RFC PATCH v11 for 4.15 01/24] Restartable sequences system call |
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----- On Nov 16, 2017, at 1:43 PM, Peter Zijlstra peterz@infradead.org wrote:
> On Tue, Nov 14, 2017 at 03:03:51PM -0500, Mathieu Desnoyers wrote: >> +/* >> + * If parent process has a registered restartable sequences area, the >> + * child inherits. Only applies when forking a process, not a thread. In >> + * case a parent fork() in the middle of a restartable sequence, set the >> + * resume notifier to force the child to retry. >> + */ >> +static inline void rseq_fork(struct task_struct *t, unsigned long clone_flags) >> +{ >> + if (clone_flags & CLONE_THREAD) { >> + t->rseq = NULL; >> + t->rseq_len = 0; >> + t->rseq_sig = 0; >> + } else { >> + t->rseq = current->rseq; >> + t->rseq_len = current->rseq_len; >> + t->rseq_sig = current->rseq_sig; >> + rseq_set_notify_resume(t); >> + } >> +} > > This hurts my brain... what happens if you fork a multi-threaded > process? > > Do we fully inherit the TLS state of the calling thread?
Yes, exactly. The user-space TLS should be inherited from that of the calling thread.
At kernel-level, the only thing that's not inherited here is the task struct rseq_event_mask, which tracks whether a restart is needed. But this would only be relevant if fork() can be invoked from a signal handler, or if fork() could be invoked from a rseq critical section (which really makes little sense).
Should I copy the current->rseq_event_mask on process fork just to be on the safe side though ?
Thanks,
Mathieu
-- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com
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