68 lines
2.1 KiB
Diff
68 lines
2.1 KiB
Diff
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From 8be1f86952a0239c1d9e89e47bc25831b1804570 Mon Sep 17 00:00:00 2001
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From: Alexander Graf <agraf@suse.de>
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Date: Fri, 13 Jan 2012 17:05:41 +0100
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Subject: [PATCH] linux-user: fix segfault deadlock
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When entering the guest we take a lock to ensure that nobody else messes
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with our TB chaining while we're doing it. If we get a segfault inside that
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code, we manage to work on, but will not unlock the lock.
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This patch forces unlocking of that lock in the segv handler. I'm not sure
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this is the right approach though. Maybe we should rather make sure we don't
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segfault in the code? I would greatly appreciate someone more intelligible
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than me to look at this :).
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Example code to trigger this is at: http://csgraf.de/tmp/conftest.c
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Reported-by: Fabio Erculiani <lxnay@sabayon.org>
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Signed-off-by: Alexander Graf <agraf@suse.de>
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---
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qemu-lock.h | 10 ++++++++++
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user-exec.c | 4 ++++
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2 files changed, 14 insertions(+), 0 deletions(-)
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diff --git a/qemu-lock.h b/qemu-lock.h
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index a72edda..e460e12 100644
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--- a/qemu-lock.h
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+++ b/qemu-lock.h
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@@ -24,6 +24,12 @@
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#include <pthread.h>
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#define spin_lock pthread_mutex_lock
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#define spin_unlock pthread_mutex_unlock
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+static inline void spin_unlock_safe(pthread_mutex_t *lock)
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+{
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+ /* unlocking an unlocked mutex results in undefined behavior */
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+ pthread_mutex_trylock(lock);
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+ pthread_mutex_unlock(lock);
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+}
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#define spinlock_t pthread_mutex_t
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#define SPIN_LOCK_UNLOCKED PTHREAD_MUTEX_INITIALIZER
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@@ -46,4 +52,8 @@ static inline void spin_unlock(spinlock_t *lock)
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{
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}
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+static inline void spin_unlock_safe(spinlock_t *lock)
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+{
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+}
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+
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#endif
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diff --git a/user-exec.c b/user-exec.c
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index abf6885..2826bd1 100644
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--- a/user-exec.c
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+++ b/user-exec.c
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@@ -96,6 +96,10 @@ static inline int handle_cpu_signal(unsigned long pc, unsigned long address,
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qemu_printf("qemu: SIGSEGV pc=0x%08lx address=%08lx w=%d oldset=0x%08lx\n",
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pc, address, is_write, *(unsigned long *)old_set);
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#endif
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+
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+ /* Maybe we're still holding the TB fiddling lock? */
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+ spin_unlock_safe(&tb_lock);
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+
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/* XXX: locking issue */
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if (is_write && page_unprotect(h2g(address), pc, puc)) {
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return 1;
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--
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1.6.0.2
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