linux-kernel - [PATCH 04/11] x86/fault: Document the locking in the fault_signal

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Message-Id: <3be55bffd65d49c6351c9e732f7b2263039a389d.1612113550.git.luto@kernel.org>
Date:   Sun, 31 Jan 2021 09:24:35 -0800
From:   Andy Lutomirski <luto@...nel.org>
To:     x86@...nel.org
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Yonghong Song <yhs@...com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>
Subject: [PATCH 04/11] x86/fault: Document the locking in the fault_signal_pending() path

If fault_signal_pending() returns true, then the core mm has unlocked the
mm for us.  Add a comment to help future readers of this code.

Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Signed-off-by: Andy Lutomirski <luto@...nel.org>
---
 arch/x86/mm/fault.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index 87d30daa5e0a..b52064920f0d 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -1343,8 +1343,11 @@ void do_user_addr_fault(struct pt_regs *regs,
 	 */
 	fault = handle_mm_fault(vma, address, flags, regs);
 
-	/* Quick path to respond to signals */
 	if (fault_signal_pending(fault, regs)) {
+		/*
+		 * Quick path to respond to signals.  The core mm code
+		 * has unlocked the mm for us if we get here.
+		 */
 		if (!user_mode(regs))
 			no_context(regs, error_code, address, SIGBUS,
 				   BUS_ADRERR);
-- 
2.29.2