linux-kernel - Re: [PATCH 4/4] riscv: remove the switch statement in do_trap

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Date:   Mon, 7 Oct 2019 09:08:23 -0700 (PDT)
From:   Paul Walmsley <paul.walmsley@...ive.com>
To:     Vincent Chen <vincent.chen@...ive.com>
cc:     Christoph Hellwig <hch@...radead.org>,
        linux-riscv@...ts.infradead.org, palmer@...ive.com,
        linux-kernel@...r.kernel.org, aou@...s.berkeley.edu
Subject: Re: [PATCH 4/4] riscv: remove the switch statement in
 do_trap_break()

Vincent,

On Fri, 27 Sep 2019, Christoph Hellwig wrote:

> On Mon, Sep 23, 2019 at 08:45:17AM +0800, Vincent Chen wrote:
> > To make the code more straightforward, replacing the switch statement
> > with if statement.
> > 
> > Suggested-by: Paul Walmsley <paul.walmsley@...ive.com>
> > Signed-off-by: Vincent Chen <vincent.chen@...ive.com>

...

> I like where this is going, but I think this can be improved further
> given that fact that report_bug has a nice stub for the
> !CONFIG_GENERIC_BUG case.
> 
> How about:
> 
> 	if (user_mode(regs))
> 		force_sig_fault(SIGTRAP, TRAP_BRKPT, (void __user *)regs->sepc);
> 	else if (report_bug(regs->sepc, regs) == BUG_TRAP_TYPE_WARN)
> 		regs->sepc += get_break_insn_length(regs->sepc);
> 	else
> 		die(regs, "Kernel BUG");
> 

Christoph's suggestion looks good to me.  What do you think about this 
modification to your patch?

- Paul


From: Vincent Chen <vincent.chen@...ive.com>
Date: Mon, 23 Sep 2019 08:45:17 +0800
Subject: [PATCH] riscv: remove the switch statement in do_trap_break()

To make the code more straightforward, replace the switch statement
with an if statement.

Suggested-by: Paul Walmsley <paul.walmsley@...ive.com>
Signed-off-by: Vincent Chen <vincent.chen@...ive.com>
[paul.walmsley@...ive.com: removed CONFIG_GENERIC_BUG tests per
 Christoph's suggestion; cleaned up patch description]
Cc: Christoph Hellwig <hch@....de>
Link: https://lore.kernel.org/linux-riscv/20190927224711.GI4700@infradead.org/
Signed-off-by: Paul Walmsley <paul.walmsley@...ive.com>
---
 arch/riscv/kernel/traps.c | 21 +++++----------------
 1 file changed, 5 insertions(+), 16 deletions(-)

diff --git a/arch/riscv/kernel/traps.c b/arch/riscv/kernel/traps.c
index 93742df9067f..45b82be00714 100644
--- a/arch/riscv/kernel/traps.c
+++ b/arch/riscv/kernel/traps.c
@@ -124,24 +124,13 @@ static inline unsigned long get_break_insn_length(unsigned long pc)
 
 asmlinkage void do_trap_break(struct pt_regs *regs)
 {
-	if (!user_mode(regs)) {
-		enum bug_trap_type type;
-
-		type = report_bug(regs->sepc, regs);
-		switch (type) {
-#ifdef CONFIG_GENERIC_BUG
-		case BUG_TRAP_TYPE_WARN:
-			regs->sepc += get_break_insn_length(regs->sepc);
-			return;
-		case BUG_TRAP_TYPE_BUG:
-#endif /* CONFIG_GENERIC_BUG */
-		default:
-			die(regs, "Kernel BUG");
-		}
-	} else {
+	if (user_mode(regs))
 		force_sig_fault(SIGTRAP, TRAP_BRKPT,
 				(void __user *)(regs->sepc));
-	}
+	else if (report_bug(regs->sepc, regs) == BUG_TRAP_TYPE_WARN)
+		regs->sepc += get_break_insn_length(regs->sepc);
+	else
+		die(regs, "Kernel BUG");
 }
 
 #ifdef CONFIG_GENERIC_BUG
-- 
2.23.0