linux-kernel - Re: [PATCH 1/7] uretprobes: preparation patch

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Date:	Sat, 23 Mar 2013 18:42:23 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Anton Arapov <anton@...hat.com>
Cc:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Josh Stone <jistone@...hat.com>,
	Frank Eigler <fche@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...e.hu>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	adrian.m.negreanu@...el.com, Torsten.Polle@....de
Subject: Re: [PATCH 1/7] uretprobes: preparation patch

On 03/22, Anton Arapov wrote:
>
> @@ -1488,10 +1496,14 @@ static void handler_chain(struct uprobe *uprobe, struct pt_regs *regs)
>  {
>  	struct uprobe_consumer *uc;
>  	int remove = UPROBE_HANDLER_REMOVE;
> +	int rc = 0;
>  
>  	down_read(&uprobe->register_rwsem);
>  	for (uc = uprobe->consumers; uc; uc = uc->next) {
> -		int rc = uc->handler(uc, regs);
> +		if (uc->handler)
> +			rc = uc->handler(uc, regs);
> +		else
> +			remove = 0;

Well, this doesn't look good. Yes, we need to conditionalize uc->handler()
and rc checks, but the code looks ugly. We touch remove twice, and the value
of rc inside the loop is bogus if ->handler == NULL.

I wouldn't have argued, but, but 4/7 changes the "else" branch and this change
is wrong (I'll write another email). We do not need this "else" at all.

I'd suggest the patch below.

Oleg.

--- x/kernel/events/uprobes.c
+++ x/kernel/events/uprobes.c
@@ -1491,10 +1491,13 @@ static void handler_chain(struct uprobe 
 
 	down_read(&uprobe->register_rwsem);
 	for (uc = uprobe->consumers; uc; uc = uc->next) {
-		int rc = uc->handler(uc, regs);
+		int rc = 0;
 
-		WARN(rc & ~UPROBE_HANDLER_MASK,
-			"bad rc=0x%x from %pf()\n", rc, uc->handler);
+		if (uc->handler) {
+			rc = uc->handler(uc, regs);
+			WARN(rc & ~UPROBE_HANDLER_MASK,
+				"bad rc=0x%x from %pf()\n", rc, uc->handler);
+		}
 		remove &= rc;
 	}
 

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