[newlib-cygwin] Cygwin: posix timers: fix a deadlock

Corinna Vinschen corinna@sourceware.org
Fri Mar 8 11:57:00 GMT 2019


commit 4ec5ffc198fcdcbea2dbca81a337900ac33b1fa7
Author: Corinna Vinschen <corinna@vinschen.de>
Date:   Fri Mar 8 12:51:10 2019 +0100

    Cygwin: posix timers: fix a deadlock
    Canceling the timer thread runs under lock.  The thread uses the same
    lock to guard its timer_tracker struct access.  If the timing is bad,
    timer_settime or timer_delete grab the lock at the same time, the timer
    expires.  In the end, cancel waits for the thread sync while the thread
    waits for ther lock to be released.
    Fix this by not waiting for the thread sync under lock.
    Signed-off-by: Corinna Vinschen <corinna@vinschen.de>

 winsup/cygwin/posix_timer.cc | 2 ++
 winsup/cygwin/release/3.0.3  | 3 +++
 2 files changed, 5 insertions(+)

diff --git a/winsup/cygwin/posix_timer.cc b/winsup/cygwin/posix_timer.cc
index a140b00..c0d548f 100644
--- a/winsup/cygwin/posix_timer.cc
+++ b/winsup/cygwin/posix_timer.cc
@@ -31,7 +31,9 @@ timer_tracker::cancel ()
   SetEvent (cancel_evt);
   if (sync_thr)
+      ReleaseSRWLockExclusive (&srwlock);
       res = WaitForSingleObject (sync_thr, INFINITE);
+      AcquireSRWLockExclusive (&srwlock);
       if (res != WAIT_OBJECT_0)
 	debug_printf ("WFSO returned unexpected value %u, %E", res);
diff --git a/winsup/cygwin/release/3.0.3 b/winsup/cygwin/release/3.0.3
index 66ae639..b8c89cb 100644
--- a/winsup/cygwin/release/3.0.3
+++ b/winsup/cygwin/release/3.0.3
@@ -11,3 +11,6 @@ Bug Fixes
 - Fix a resource leak in posix timers.
   Addresses: https://cygwin.com/ml/cygwin/2019-03/msg00120.html
+- Fix a deadlock in posix timers
+  Addresses: https://cygwin.com/ml/cygwin/2019-03/msg00158.html

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