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From: Andreas Schwab <schwab@sourceware.org> To: glibc-cvs@sourceware.org Subject: [glibc] nptl: wait for pending setxid request also in detached thread (bug 25942) Date: Tue, 12 May 2020 15:23:09 +0000 (GMT) [thread overview] Message-ID: <20200512152309.1878A386F02B@sourceware.org> (raw) https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=4cab20fa49b3ea3e3454fdc4f13bf3828d8efd19 commit 4cab20fa49b3ea3e3454fdc4f13bf3828d8efd19 Author: Andreas Schwab <schwab@suse.de> Date: Thu May 7 15:50:09 2020 +0200 nptl: wait for pending setxid request also in detached thread (bug 25942) There is a race between __nptl_setxid and exiting detached thread, which causes a deadlock on stack_cache_lock. The deadlock happens in this state: T1: setgroups -> __nptl_setxid (holding stack_cache_lock, waiting on cmdp->cntr == 0) T2 (detached, exiting): start_thread -> __deallocate_stack (waiting on stack_cache_lock) more threads waiting on stack_cache_lock in pthread_create For non-detached threads, start_thread waits for its own setxid handler to finish before exiting. Do this for detached threads as well. Diff: --- nptl/pthread_create.c | 11 ++++++----- 1 file changed, 6 insertions(+), 5 deletions(-) diff --git a/nptl/pthread_create.c b/nptl/pthread_create.c index afd379e89a..a43089065c 100644 --- a/nptl/pthread_create.c +++ b/nptl/pthread_create.c @@ -552,11 +552,7 @@ START_THREAD_DEFN advise_stack_range (pd->stackblock, pd->stackblock_size, (uintptr_t) pd, pd->guardsize); - /* If the thread is detached free the TCB. */ - if (IS_DETACHED (pd)) - /* Free the TCB. */ - __free_tcb (pd); - else if (__glibc_unlikely (pd->cancelhandling & SETXID_BITMASK)) + if (__glibc_unlikely (pd->cancelhandling & SETXID_BITMASK)) { /* Some other thread might call any of the setXid functions and expect us to reply. In this case wait until we did that. */ @@ -572,6 +568,11 @@ START_THREAD_DEFN pd->setxid_futex = 0; } + /* If the thread is detached free the TCB. */ + if (IS_DETACHED (pd)) + /* Free the TCB. */ + __free_tcb (pd); + /* We cannot call '_exit' here. '_exit' will terminate the process. The 'exit' implementation in the kernel will signal when the
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