linux-kernel - [PATCH v2] xtensa: fix broken TIF_NOTIFY

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Date:   Wed, 11 Nov 2020 12:53:49 -0800
From:   Max Filippov <jcmvbkbc@...il.com>
To:     linux-xtensa@...ux-xtensa.org
Cc:     Chris Zankel <chris@...kel.net>, linux-kernel@...r.kernel.org,
        Max Filippov <jcmvbkbc@...il.com>, Jens Axboe <axboe@...nel.dk>
Subject: [PATCH v2] xtensa: fix broken TIF_NOTIFY_SIGNAL assembly

TIF_NOTIFY_SIGNAL handling in xtensa assembly is implemented
incorrectly: there should be a call to do_notify_resume when either
TIF_SIGPENDING, TIF_NOTIFY_RESUME or TIF_NOTIFY_SIGNAL bit is set in the
thread_info::flags. The straightforward way to do it would be

    _bbsi.l a4, TIF_NEED_RESCHED, 3f
    _bbsi.l a4, TIF_NOTIFY_RESUME, 2f
    _bbsi.l a4, TIF_NOTIFY_SIGNAL, 2f
    _bbci.l a4, TIF_SIGPENDING, 5f

Optimize it a little bit and use bit mask and bnone opcode to skip
do_notify_resume invocation. Shuffle _TIF_* flags a bit so that used bit
mask fits into the immediate field of movi opcode.

Fixes: 4c6a9dcd4d13 ("xtensa: add support for TIF_NOTIFY_SIGNAL")
Cc: Jens Axboe <axboe@...nel.dk>
Signed-off-by: Max Filippov <jcmvbkbc@...il.com>
---
Changes v1->v2:
- use more canonical order of bnone arguments: tested value first,
  bit mask second.

 arch/xtensa/include/asm/thread_info.h | 7 ++++---
 arch/xtensa/kernel/entry.S            | 5 ++---
 2 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/arch/xtensa/include/asm/thread_info.h b/arch/xtensa/include/asm/thread_info.h
index 6ea521b8e2ec..a312333a9add 100644
--- a/arch/xtensa/include/asm/thread_info.h
+++ b/arch/xtensa/include/asm/thread_info.h
@@ -111,22 +111,23 @@ static inline struct thread_info *current_thread_info(void)
 #define TIF_NEED_RESCHED	2	/* rescheduling necessary */
 #define TIF_SINGLESTEP		3	/* restore singlestep on return to user mode */
 #define TIF_SYSCALL_TRACEPOINT	4	/* syscall tracepoint instrumentation */
-#define TIF_MEMDIE		5	/* is terminating due to OOM killer */
+#define TIF_NOTIFY_SIGNAL	5	/* signal notifications exist */
 #define TIF_RESTORE_SIGMASK	6	/* restore signal mask in do_signal() */
 #define TIF_NOTIFY_RESUME	7	/* callback before returning to user */
 #define TIF_DB_DISABLED		8	/* debug trap disabled for syscall */
 #define TIF_SYSCALL_AUDIT	9	/* syscall auditing active */
 #define TIF_SECCOMP		10	/* secure computing */
-#define TIF_NOTIFY_SIGNAL	11	/* signal notifications exist */
+#define TIF_MEMDIE		11	/* is terminating due to OOM killer */
 
 #define _TIF_SYSCALL_TRACE	(1<<TIF_SYSCALL_TRACE)
 #define _TIF_SIGPENDING		(1<<TIF_SIGPENDING)
 #define _TIF_NEED_RESCHED	(1<<TIF_NEED_RESCHED)
 #define _TIF_SINGLESTEP		(1<<TIF_SINGLESTEP)
 #define _TIF_SYSCALL_TRACEPOINT	(1<<TIF_SYSCALL_TRACEPOINT)
+#define _TIF_NOTIFY_SIGNAL	(1<<TIF_NOTIFY_SIGNAL)
+#define _TIF_NOTIFY_RESUME	(1<<TIF_NOTIFY_RESUME)
 #define _TIF_SYSCALL_AUDIT	(1<<TIF_SYSCALL_AUDIT)
 #define _TIF_SECCOMP		(1<<TIF_SECCOMP)
-#define _TIF_NOTIFY_SIGNAL	(1<<TIF_NOTIFY_SIGNAL)
 
 #define _TIF_WORK_MASK		(_TIF_SYSCALL_TRACE | _TIF_SINGLESTEP | \
 				 _TIF_SYSCALL_TRACEPOINT | \
diff --git a/arch/xtensa/kernel/entry.S b/arch/xtensa/kernel/entry.S
index 7f733f40fef0..647b162f959b 100644
--- a/arch/xtensa/kernel/entry.S
+++ b/arch/xtensa/kernel/entry.S
@@ -500,9 +500,8 @@ common_exception_return:
 	 */
 
 	_bbsi.l	a4, TIF_NEED_RESCHED, 3f
-	_bbsi.l	a4, TIF_NOTIFY_RESUME, 2f
-	_bbci.l	a4, TIF_SIGPENDING, 5f
-	_bbci.l	a4, TIF_NOTIFY_SIGNAL, 5f
+	movi	a2, _TIF_SIGPENDING | _TIF_NOTIFY_RESUME | _TIF_NOTIFY_SIGNAL
+	bnone	a4, a2, 5f
 
 2:	l32i	a4, a1, PT_DEPC
 	bgeui	a4, VALID_DOUBLE_EXCEPTION_ADDRESS, 4f
-- 
2.20.1