File 0017-linux-user-fix-segfault-deadlock.pa.patch of Package qemu

Overview Repositories Revisions Requests Users Attributes Meta

File 0017-linux-user-fix-segfault-deadlock.pa.patch of Package qemu (Revision d4c501d883151c99c6e3c2d7f5ec7497)

Currently displaying revision d4c501d883151c99c6e3c2d7f5ec7497 , Show latest

From 76d1a76b0286e02aa575faad3556f73481ade1b2 Mon Sep 17 00:00:00 2001
From: Alexander Graf <agraf@suse.de>
Date: Fri, 13 Jan 2012 17:05:41 +0100
Subject: [PATCH] linux-user: fix segfault deadlock

When entering the guest we take a lock to ensure that nobody else messes
with our TB chaining while we're doing it. If we get a segfault inside that
code, we manage to work on, but will not unlock the lock.

This patch forces unlocking of that lock in the segv handler. I'm not sure
this is the right approach though. Maybe we should rather make sure we don't
segfault in the code? I would greatly appreciate someone more intelligible
than me to look at this :).

Example code to trigger this is at: http://csgraf.de/tmp/conftest.c

Reported-by: Fabio Erculiani <lxnay@sabayon.org>
Signed-off-by: Alexander Graf <agraf@suse.de>
---
 qemu-lock.h |   10 ++++++++++
 user-exec.c |    4 ++++
 2 files changed, 14 insertions(+), 0 deletions(-)

diff --git a/qemu-lock.h b/qemu-lock.h
index a72edda..e460e12 100644
--- a/qemu-lock.h
+++ b/qemu-lock.h
@@ -24,6 +24,12 @@
 #include <pthread.h>
 #define spin_lock pthread_mutex_lock
 #define spin_unlock pthread_mutex_unlock
+static inline void spin_unlock_safe(pthread_mutex_t *lock)
+{
+    /* unlocking an unlocked mutex results in undefined behavior */
+    pthread_mutex_trylock(lock);
+    pthread_mutex_unlock(lock);
+}
 #define spinlock_t pthread_mutex_t
 #define SPIN_LOCK_UNLOCKED PTHREAD_MUTEX_INITIALIZER
 
@@ -46,4 +52,8 @@ static inline void spin_unlock(spinlock_t *lock)
 {
 }
 
+static inline void spin_unlock_safe(spinlock_t *lock)
+{
+}
+
 #endif
diff --git a/user-exec.c b/user-exec.c
index b9ea9dd..5a04218 100644
--- a/user-exec.c
+++ b/user-exec.c
@@ -102,6 +102,10 @@ static inline int handle_cpu_signal(uintptr_t pc, unsigned long address,
     qemu_printf("qemu: SIGSEGV pc=0x%08lx address=%08lx w=%d oldset=0x%08lx\n",
                 pc, address, is_write, *(unsigned long *)old_set);
 #endif
+
+    /* Maybe we're still holding the TB fiddling lock? */
+    spin_unlock_safe(&tb_lock);
+
     /* XXX: locking issue */
     if (is_write && h2g_valid(address)
         && page_unprotect(h2g(address), pc, puc)) {

Places

File 0017-linux-user-fix-segfault-deadlock.pa.patch of Package qemu (Revision d4c501d883151c99c6e3c2d7f5ec7497)

Places