Patchwork [v2,1/2] Fix robust mutex daedlock [BZ #20263]

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Submitter Jiyoung Yun
Date June 29, 2016, 3:03 p.m.
Message ID <1467212621-5522-2-git-send-email-t2wish@gmail.com>
Download mbox | patch
Permalink /patch/13488/
State New
Headers show

Comments

Jiyoung Yun - June 29, 2016, 3:03 p.m.
In Linux/ARM environment, a robust mutex can't catch the timeout result
when it is already owned by other thread and requests to try lock with
a specific time value(pthread_mutex_timedlock). The futex already returns
the ETIMEDOUT result but there is no check the return value and it makes
a deadlock.

* nptl/lowlevelrobustlock.c: Implement ETIMEDOUT logic.
---
 ChangeLog                 | 5 +++++
 nptl/lowlevelrobustlock.c | 9 +++++++--
 2 files changed, 12 insertions(+), 2 deletions(-)
Andreas Schwab - June 29, 2016, 3:22 p.m.
Jiyoung Yun <t2wish@gmail.com> writes:

> diff --git a/nptl/lowlevelrobustlock.c b/nptl/lowlevelrobustlock.c
> index 3b988b2..e5d3758 100644
> --- a/nptl/lowlevelrobustlock.c
> +++ b/nptl/lowlevelrobustlock.c
> @@ -113,15 +113,20 @@ __lll_robust_timedlock_wait (int *futex, const struct timespec *abstime,
>  	  && atomic_compare_and_exchange_bool_acq (futex, newval, oldval))
>  	continue;
>  
> +      int err;
>        /* If *futex == 2, wait until woken or timeout.  */
>  #if (!defined __ASSUME_FUTEX_CLOCK_REALTIME \
>       || !defined lll_futex_timed_wait_bitset)
> -      lll_futex_timed_wait (futex, newval, &rt, private);
> +      err = lll_futex_timed_wait (futex, newval, &rt, private);

I don't think this call should be checked for timeout because we want to
check the absolute time, not the relative time we computed here.

Andreas.
Andreas Schwab - June 29, 2016, 3:41 p.m.
Jiyoung Yun <t2wish@gmail.com> writes:

> And the same problem can be occured in case of the relative time too,
> doesn't it?

No, it doesn't, see the top of the loop.

Andreas.

Patch

diff --git a/ChangeLog b/ChangeLog
index 3da2eca..97461f6 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@ 
+2016-06-28  Jiyoung Yun  <t2wish@gmail.com>
+
+	[BZ #20263]
+	* nptl/lowlevelrobustlock.c: Implement ETIMEDOUT logic.
+
 2016-06-28  Richard Henderson  <rth@redhat.com>
 
 	* elf/elf.h (EM_BPF): New.
diff --git a/nptl/lowlevelrobustlock.c b/nptl/lowlevelrobustlock.c
index 3b988b2..e5d3758 100644
--- a/nptl/lowlevelrobustlock.c
+++ b/nptl/lowlevelrobustlock.c
@@ -113,15 +113,20 @@  __lll_robust_timedlock_wait (int *futex, const struct timespec *abstime,
 	  && atomic_compare_and_exchange_bool_acq (futex, newval, oldval))
 	continue;
 
+      int err;
       /* If *futex == 2, wait until woken or timeout.  */
 #if (!defined __ASSUME_FUTEX_CLOCK_REALTIME \
      || !defined lll_futex_timed_wait_bitset)
-      lll_futex_timed_wait (futex, newval, &rt, private);
+      err = lll_futex_timed_wait (futex, newval, &rt, private);
 #else
-      lll_futex_timed_wait_bitset (futex, newval, abstime,
+      err = lll_futex_timed_wait_bitset (futex, newval, abstime,
 				   FUTEX_CLOCK_REALTIME, private);
 #endif
 
+      /* the futex call time out */
+      if (err == -ETIMEDOUT)
+         return -err;
+
     try:
       ;
     }