accel/tcg/cputlb: avoid recursive BQL (fixes #1706296)

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>
(cherry picked from commit 8b81253332b5a3f3c67b6462f39caef47a00dd29)
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>

diff --git a/accel/tcg/cputlb.c b/accel/tcg/cputlb.c
index 85635ae8ad6632fefbc92c91e6887a5e05b93e63..140d73a308ae832f16e45f8ac80b247257e0f70e 100644 (file)
--- a/accel/tcg/cputlb.c
+++ b/accel/tcg/cputlb.c
@@ -763,7 +763,7 @@ 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;
     }
@@ -791,7 +791,7 @@ 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;
     }