[glibc/release/2.35/master] __check_pf: Add a cancellation cleanup handler [BZ #20975]

[H.J. Lu <hjl@sourceware.org>]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=2b9906f9a0f27c1ffa329f23ae1664bc9925df0f

commit 2b9906f9a0f27c1ffa329f23ae1664bc9925df0f
Author: H.J. Lu <hjl.tools@gmail.com>
Date:   Thu Apr 27 13:06:15 2023 -0700

    __check_pf: Add a cancellation cleanup handler [BZ #20975]
    
    There are reports for hang in __check_pf:
    
    https://github.com/JoeDog/siege/issues/4
    
    It is reproducible only under specific configurations:
    
    1. Large number of cores (>= 64) and large number of threads (> 3X of
    the number of cores) with long lived socket connection.
    2. Low power (frequency) mode.
    3. Power management is enabled.
    
    While holding lock, __check_pf calls make_request which calls __sendto
    and __recvmsg.  Since __sendto and __recvmsg are cancellation points,
    lock held by __check_pf won't be released and can cause deadlock when
    thread cancellation happens in __sendto or __recvmsg.  Add a cancellation
    cleanup handler for __check_pf to unlock the lock when cancelled by
    another thread.  This fixes BZ #20975 and the siege hang issue.
    
    (cherry picked from commit a443bd3fb233186038b8b483959ecb7978d1abea)

Diff:
---
 sysdeps/unix/sysv/linux/Makefile   |  2 ++
 sysdeps/unix/sysv/linux/check_pf.c | 15 +++++++++++++++
 2 files changed, 17 insertions(+)

diff --git a/sysdeps/unix/sysv/linux/Makefile b/sysdeps/unix/sysv/linux/Makefile
index e897f55f3a..21bcd1920a 100644
--- a/sysdeps/unix/sysv/linux/Makefile
+++ b/sysdeps/unix/sysv/linux/Makefile
@@ -326,6 +326,8 @@ sysdep_headers += netinet/if_fddi.h netinet/if_tr.h \
 		  netrom/netrom.h netpacket/packet.h netrose/rose.h \
 		  neteconet/ec.h netiucv/iucv.h
 sysdep_routines += netlink_assert_response
+
+CFLAGS-check_pf.c += -fexceptions
 endif
 
 # Don't compile the ctype glue code, since there is no old non-GNU C library.
diff --git a/sysdeps/unix/sysv/linux/check_pf.c b/sysdeps/unix/sysv/linux/check_pf.c
index fe73fe3ba8..ca20043408 100644
--- a/sysdeps/unix/sysv/linux/check_pf.c
+++ b/sysdeps/unix/sysv/linux/check_pf.c
@@ -292,6 +292,14 @@ make_request (int fd, pid_t pid)
   return NULL;
 }
 
+#ifdef __EXCEPTIONS
+static void
+cancel_handler (void *arg __attribute__((unused)))
+{
+  /* Release the lock.  */
+  __libc_lock_unlock (lock);
+}
+#endif
 
 void
 attribute_hidden
@@ -304,6 +312,10 @@ __check_pf (bool *seen_ipv4, bool *seen_ipv6,
   struct cached_data *olddata = NULL;
   struct cached_data *data = NULL;
 
+#ifdef __EXCEPTIONS
+  /* Make sure that lock is released when the thread is cancelled.  */
+  __libc_cleanup_push (cancel_handler, NULL);
+#endif
   __libc_lock_lock (lock);
 
   if (cache_valid_p ())
@@ -338,6 +350,9 @@ __check_pf (bool *seen_ipv4, bool *seen_ipv6,
 	}
     }
 
+#ifdef __EXCEPTIONS
+  __libc_cleanup_pop (0);
+#endif
   __libc_lock_unlock (lock);
 
   if (data != NULL)