linux-kernel - [PATCH 3/6] kernel: split syscall restart from signal handling

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Date:   Mon,  5 Oct 2020 09:04:35 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     linux-kernel@...r.kernel.org, io-uring@...r.kernel.org
Cc:     peterz@...radead.org, oleg@...hat.com, tglx@...utronix.de,
        Jens Axboe <axboe@...nel.dk>
Subject: [PATCH 3/6] kernel: split syscall restart from signal handling

Move the restart syscall logic into a separate generic entry helper,
and handle that part separately from signal checking and delivery.

This is in preparation for being able to do syscall restarting
independently from handling signals.

Signed-off-by: Jens Axboe <axboe@...nel.dk>
---
 arch/x86/kernel/signal.c     | 32 ++++++++++++++++++--------------
 include/linux/entry-common.h | 14 ++++++++++++--
 kernel/entry/common.c        | 11 ++++++++---
 3 files changed, 38 insertions(+), 19 deletions(-)

diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c
index be0d7d4152ec..5dc1eeaf0866 100644
--- a/arch/x86/kernel/signal.c
+++ b/arch/x86/kernel/signal.c
@@ -799,21 +799,8 @@ static inline unsigned long get_nr_restart_syscall(const struct pt_regs *regs)
 #endif
 }
 
-/*
- * Note that 'init' is a special process: it doesn't get signals it doesn't
- * want to handle. Thus you cannot kill init even with a SIGKILL even by
- * mistake.
- */
-void arch_do_signal(struct pt_regs *regs)
+void arch_restart_syscall(struct pt_regs *regs)
 {
-	struct ksignal ksig;
-
-	if (get_signal(&ksig)) {
-		/* Whee! Actually deliver the signal.  */
-		handle_signal(&ksig, regs);
-		return;
-	}
-
 	/* Did we come from a system call? */
 	if (syscall_get_nr(current, regs) >= 0) {
 		/* Restart the system call - no handlers present */
@@ -831,12 +818,29 @@ void arch_do_signal(struct pt_regs *regs)
 			break;
 		}
 	}
+}
+
+/*
+ * Note that 'init' is a special process: it doesn't get signals it doesn't
+ * want to handle. Thus you cannot kill init even with a SIGKILL even by
+ * mistake.
+ */
+bool arch_do_signal(struct pt_regs *regs)
+{
+	struct ksignal ksig;
+
+	if (get_signal(&ksig)) {
+		/* Whee! Actually deliver the signal.  */
+		handle_signal(&ksig, regs);
+		return true;
+	}
 
 	/*
 	 * If there's no signal to deliver, we just put the saved sigmask
 	 * back.
 	 */
 	restore_saved_sigmask();
+	return false;
 }
 
 void signal_fault(struct pt_regs *regs, void __user *frame, char *where)
diff --git a/include/linux/entry-common.h b/include/linux/entry-common.h
index 159c7476b11b..ccfcc4769925 100644
--- a/include/linux/entry-common.h
+++ b/include/linux/entry-common.h
@@ -262,9 +262,19 @@ static __always_inline void arch_exit_to_user_mode(void) { }
  * arch_do_signal -  Architecture specific signal delivery function
  * @regs:	Pointer to currents pt_regs
  *
- * Invoked from exit_to_user_mode_loop().
+ * Invoked from exit_to_user_mode_loop(). Returns true if a signal was
+ * handled.
  */
-void arch_do_signal(struct pt_regs *regs);
+bool arch_do_signal(struct pt_regs *regs);
+
+/**
+ * arch_restart_syscall -  Architecture specific syscall restarting
+ * @regs:	Pointer to currents pt_regs
+ *
+ * Invoked from exit_to_user_mode_loop(), if we need to restart the current
+ * system call.
+ */
+void arch_restart_syscall(struct pt_regs *regs);
 
 /**
  * arch_syscall_exit_tracehook - Wrapper around tracehook_report_syscall_exit()
diff --git a/kernel/entry/common.c b/kernel/entry/common.c
index d20ab4ac7183..0c0cc3cf3eba 100644
--- a/kernel/entry/common.c
+++ b/kernel/entry/common.c
@@ -135,11 +135,13 @@ static __always_inline void exit_to_user_mode(void)
 }
 
 /* Workaround to allow gradual conversion of architecture code */
-void __weak arch_do_signal(struct pt_regs *regs) { }
+bool __weak arch_do_signal(struct pt_regs *regs) { return true; }
 
 static unsigned long exit_to_user_mode_loop(struct pt_regs *regs,
 					    unsigned long ti_work)
 {
+	bool restart_sys = ti_work & _TIF_SIGPENDING;
+
 	/*
 	 * Before returning to user space ensure that all pending work
 	 * items have been completed.
@@ -157,8 +159,8 @@ static unsigned long exit_to_user_mode_loop(struct pt_regs *regs,
 		if (ti_work & _TIF_PATCH_PENDING)
 			klp_update_patch_state(current);
 
-		if (ti_work & _TIF_SIGPENDING)
-			arch_do_signal(regs);
+		if ((ti_work & _TIF_SIGPENDING) && arch_do_signal(regs))
+			restart_sys = false;
 
 		if (ti_work & _TIF_NOTIFY_RESUME) {
 			tracehook_notify_resume(regs);
@@ -177,6 +179,9 @@ static unsigned long exit_to_user_mode_loop(struct pt_regs *regs,
 		ti_work = READ_ONCE(current_thread_info()->flags);
 	}
 
+	if (restart_sys)
+		arch_restart_syscall(regs);
+
 	/* Return the latest work state for arch_exit_to_user_mode() */
 	return ti_work;
 }
-- 
2.28.0