From: Alex Bennée <alex.bennee@linaro.org>

The mmio path (see exec.c:prepare_mmio_access) already protects itself
against recursive locking and it makes sense to do the same for
io_readx/writex. Otherwise any helper running in the BQL context will
assert when it attempts to write to device memory as in the case of
the bug report.

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
CC: Richard Jones <rjones@redhat.com>
CC: Paolo Bonzini <bonzini@gnu.org>
CC: qemu-stable@nongnu.org
Message-Id: <20170921110625.9500-1-alex.bennee@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
 accel/tcg/cputlb.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/accel/tcg/cputlb.c b/accel/tcg/cputlb.c
index e72415a882..bcbcc4db6c 100644
--- a/accel/tcg/cputlb.c
+++ b/accel/tcg/cputlb.c
@@ -765,7 +765,7 @@ static uint64_t io_readx(CPUArchState *env, CPUIOTLBEntry *iotlbentry,
 
     cpu->mem_io_vaddr = addr;
 
-    if (mr->global_locking) {
+    if (mr->global_locking && !qemu_mutex_iothread_locked()) {
         qemu_mutex_lock_iothread();
         locked = true;
     }
@@ -800,7 +800,7 @@ static void io_writex(CPUArchState *env, CPUIOTLBEntry *iotlbentry,
     cpu->mem_io_vaddr = addr;
     cpu->mem_io_pc = retaddr;
 
-    if (mr->global_locking) {
+    if (mr->global_locking && !qemu_mutex_iothread_locked()) {
         qemu_mutex_lock_iothread();
         locked = true;
     }
-- 
2.13.5