File 0012-linux-user-fix-segfault-deadlock.patch of Package qemu.4225

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File 0012-linux-user-fix-segfault-deadlock.patch of Package qemu.4225

From 0b4c7b3388d69eed74e64664311b519b8552f2c9 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
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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>
[AF: Drop spinlock_safe_unlock() and switch to tb_lock_reset() (bonzini)]
Signed-off-by: Andreas Färber <afaerber@suse.de>
Signed-off-by: Bruce Rogers <brogers@suse.com>
---
 user-exec.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/user-exec.c b/user-exec.c
index d8d597bafe..f8b7752671 100644
--- a/user-exec.c
+++ b/user-exec.c
@@ -94,6 +94,10 @@ static inline int handle_cpu_signal(uintptr_t pc, unsigned long address,
     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? */
+    tb_lock_reset();
+
     /* XXX: locking issue */
     if (is_write && h2g_valid(address)
         && page_unprotect(h2g(address), pc, puc)) {

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File 0012-linux-user-fix-segfault-deadlock.patch of Package qemu.4225

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