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From 4cab20fa49b3ea3e3454fdc4f13bf3828d8efd19 Mon Sep 17 00:00:00 2001
From: Andreas Schwab <schwab@suse.de>
Date: Thu, 7 May 2020 15:50:09 +0200
Subject: [PATCH] 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.
---
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
@@ -567,11 +567,7 @@ 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. */
@@ -587,6 +583,11 @@ 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
--
2.19.1
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