linux-kernel - [PATCH 3/3] riscv/signal: Fixup additional syscall restarting

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Date:   Tue,  2 Apr 2019 16:02:33 +0800
From:   guoren@...nel.org
To:     arnd@...db.de, palmer@...ive.com
Cc:     linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        ren_guo@...ky.com, linux-riscv@...ts.infradead.org
Subject: [PATCH 3/3] riscv/signal: Fixup additional syscall restarting

From: Guo Ren <ren_guo@...ky.com>

The function of do_notify_resume called by entry.S could be entered
in loop when SIGPENDING was setted again before sret. So we must add
prevent code to make syscall restart (regs->sepc -= 0x4) or it may
re-execute unexpected instructions.

Just like in_syscall & forget_syscall used by arm.

Signed-off-by: Guo Ren <ren_guo@...ky.com>
Cc: Palmer Dabbelt <palmer@...ive.com>
Cc: Arnd Bergmann <arnd@...db.de>
---
 arch/riscv/kernel/signal.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/arch/riscv/kernel/signal.c b/arch/riscv/kernel/signal.c
index 837e164..804d6ee 100644
--- a/arch/riscv/kernel/signal.c
+++ b/arch/riscv/kernel/signal.c
@@ -234,6 +234,9 @@ static void handle_signal(struct ksignal *ksig, struct pt_regs *regs)
 
 	/* Are we from a system call? */
 	if (regs->scause == EXC_SYSCALL) {
+		/* Avoid additional syscall restarting via ret_from_exception */
+		regs->scause = -1UL;
+
 		/* If so, check system call restarting.. */
 		switch (regs->a0) {
 		case -ERESTART_RESTARTBLOCK:
@@ -272,6 +275,9 @@ static void do_signal(struct pt_regs *regs)
 
 	/* Did we come from a system call? */
 	if (regs->scause == EXC_SYSCALL) {
+		/* Avoid additional syscall restarting via ret_from_exception */
+		regs->scause = -1UL;
+
 		/* Restart the system call - no handlers present */
 		switch (regs->a0) {
 		case -ERESTARTNOHAND:
-- 
2.7.4