Date: Thu, 25 May 2023 18:53:19 +0200 From: Markus Wichmann <nullplan@....net> To: musl@...ts.openwall.com Subject: vm lock needed in mprotect? Hi all, I'm wondering if the vm lock is needed in mprotect(), similar to munmap(). Reason for the vm lock was that if an application had two threads waiting on a process-shared barrier, and one thread came out of it to immediately unmap the SHM segment, then the other thread might not yet have had a change to exit pthread_barrier_wait(), and since that function accesses the barrier object after the last futex wait call, it would crash. So what if that first thread, instead of unmapping the SHM, just changes its protection to read-only? That would also crash. Or is that somehow not valid? If so, why? Ciao, Markus
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