about summary refs log tree commit diff
path: root/sysdeps/unix/sysv/linux/s390
diff options
context:
space:
mode:
authorStefan Liebler <stli@linux.vnet.ibm.com>2018-05-04 10:00:59 +0200
committerStefan Liebler <stli@linux.vnet.ibm.com>2018-05-04 10:00:59 +0200
commit1660901840dfc9fde6c5720a32f901af6f08f00a (patch)
treefea79b57e81f2dcaaf7d5c15fa37d31ced9beef3 /sysdeps/unix/sysv/linux/s390
parent15c19147a8361b7281519b9784b3b823c447cf7a (diff)
downloadglibc-1660901840dfc9fde6c5720a32f901af6f08f00a.tar.gz
glibc-1660901840dfc9fde6c5720a32f901af6f08f00a.tar.xz
glibc-1660901840dfc9fde6c5720a32f901af6f08f00a.zip
Fix blocking pthread_join. [BZ #23137]
On s390 (31bit) if glibc is build with -Os, pthread_join sometimes
blocks indefinitely. This is e.g. observable with
testcase intl/tst-gettext6.

pthread_join is calling lll_wait_tid(tid), which performs the futex-wait
syscall in a loop as long as tid != 0 (thread is alive).

On s390 (and build with -Os), tid is loaded from memory before
comparing against zero and then the tid is loaded a second time
in order to pass it to the futex-wait-syscall.
If the thread exits in between, then the futex-wait-syscall is
called with the value zero and it waits until a futex-wake occurs.
As the thread is already exited, there won't be a futex-wake.

In lll_wait_tid, the tid is stored to the local variable __tid,
which is then used as argument for the futex-wait-syscall.
But unfortunately the compiler is allowed to reload the value
from memory.

With this patch, the tid is loaded with atomic_load_acquire.
Then the compiler is not allowed to reload the value for __tid from memory.

ChangeLog:

	[BZ #23137]
	* sysdeps/nptl/lowlevellock.h (lll_wait_tid):
	Use atomic_load_acquire to load __tid.
Diffstat (limited to 'sysdeps/unix/sysv/linux/s390')
0 files changed, 0 insertions, 0 deletions