MIPS: Add syscall detection for restartable sequences

Syscalls are not allowed inside restartable sequences, so add a call to
rseq_syscall() at the very beginning of the system call exit path when
CONFIG_DEBUG_RSEQ=y. This will help us to detect whether there is a
syscall issued erroneously inside a restartable sequence.

Signed-off-by: Paul Burton <paul.burton@mips.com>
Reviewed-by: James Hogan <jhogan@kernel.org>
Patchwork: https://patchwork.linux-mips.org/patch/19522/
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org

1 files changed, 8 insertions, 0 deletions

diff --git a/arch/mips/kernel/entry.S b/arch/mips/kernel/entry.S
index 38a302919e6b..d7de8adcfcc8 100644
--- a/arch/mips/kernel/entry.S
+++ b/arch/mips/kernel/entry.S
@@ -79,6 +79,10 @@ FEXPORT(ret_from_fork)
         jal     schedule_tail           # a0 = struct task_struct *prev
 
 FEXPORT(syscall_exit)
+#ifdef CONFIG_DEBUG_RSEQ
+        move    a0, sp
+        jal     rseq_syscall
+#endif
         local_irq_disable               # make sure need_resched and
                                         # signals dont change between
                                         # sampling and return
@@ -141,6 +145,10 @@ work_notifysig:				# deal with pending signals and
         j       resume_userspace_check
 
 FEXPORT(syscall_exit_partial)
+#ifdef CONFIG_DEBUG_RSEQ
+        move    a0, sp
+        jal     rseq_syscall
+#endif
         local_irq_disable               # make sure need_resched doesn't
                                         # change between and return
         LONG_L  a2, TI_FLAGS($28)       # current->work