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* [glibc/release/2.36/master] __check_pf: Add a cancellation cleanup handler [BZ #20975]
@ 2023-05-23 20:10 H.J. Lu
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From: H.J. Lu @ 2023-05-23 20:10 UTC (permalink / raw)
To: glibc-cvs
https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=7df9a276563e201fd5680c46f0d8c6f719ce1fc9
commit 7df9a276563e201fd5680c46f0d8c6f719ce1fc9
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 3ceda9fdbf..d5d9af4de2 100644
--- a/sysdeps/unix/sysv/linux/Makefile
+++ b/sysdeps/unix/sysv/linux/Makefile
@@ -362,6 +362,8 @@ 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)
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