Hide Forgot
Created attachment 1721818 [details] hang.c Previous versions of glibc used a different approach, now, if a thread calls pthread_atfork from an atfork handler, it will dead lock, attempting to get the lock, hold during run of the handler. Looks similar, or same root cause, to issue reported at https://sourceware.org/bugzilla/show_bug.cgi?id=24595 [[2.28 Regression]: Deadlock in atfork handler which calls dlclose] The sample hang.c, compiled with: $ gcc -pthread -o hang hang.c will show the dead lock.
The problem is this: static void __attribute__((constructor)) init(void) { pthread_atfork(NULL, NULL, init); } This recursive call into the fork subsystem now deadlocks. An upstream patch has been posted: https://sourceware.org/bugzilla/show_bug.cgi?id=24595#c1 There were some concerns about this patch. The key point will be not to call any callback functions while implementation locks are held. With glibc, re-registering fork handlers after fork (in the subprocess) is not necessary because they are automatically inherited. This is likely not POSIX-compliant, but is long-standing glibc behavior, and it cannot be changed. So as a workaround, you can change this: static void __attribute__((constructor)) init(void) { pthread_atfork(NULL, NULL, init); } to: static void handler(void) { // Real fork handler here. } static void __attribute__((constructor)) init(void) { pthread_atfork(NULL, NULL, handler); }
Patches for this are now under review upstream: https://patchwork.sourceware.org/project/glibc/patch/20220427134625.3759831-1-arjun@redhat.com/
Since the problem described in this bug report should be resolved in a recent advisory, it has been closed with a resolution of ERRATA. For information on the advisory (glibc bug fix and enhancement update), and where to find the updated files, follow the link below. If the solution does not work for you, open a new bug report. https://access.redhat.com/errata/RHBA-2022:7684