linux-kernel - Re: signals logged / [RFC] log out-of-virtual-memory events

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Date:	Sun, 20 May 2007 22:55:00 +0200
From:	Folkert van Heusden <folkert@...heusden.com>
To:	Jan Engelhardt <jengelh@...ux01.gwdg.de>
Cc:	Stephen Hemminger <shemminger@...ux-foundation.org>,
	Eric Dumazet <dada1@...mosbay.com>, Andi Kleen <ak@...e.de>,
	Rik van Riel <riel@...hat.com>,
	righiandr@...rs.sourceforge.net,
	LKML <linux-kernel@...r.kernel.org>, linux-mm@...ck.org
Subject: Re: signals logged / [RFC] log out-of-virtual-memory events

> >> >  
> >> > +	if (unlikely(sig == SIGQUIT || sig == SIGILL  || sig == SIGTRAP ||
> >> > +	    sig == SIGABRT || sig == SIGBUS  || sig == SIGFPE  ||
> >> > +	    sig == SIGSEGV || sig == SIGXCPU || sig == SIGXFSZ ||
> >> > +	    sig == SIGSYS  || sig == SIGSTKFLT))
> >> > +	{
> >> > +		printk(KERN_WARNING "Sig %d send to %d owned by %d.%d (%s)\n",
> >> > +			sig, t->pid, t->uid, t->gid, t->comm);
> >> > +	}
> >> > +
> >> >  	/*
> >> >  	 * fast-pathed signals for kernel-internal things like SIGSTOP
> >> >  	 * or SIGKILL.
> >> Would turning that into a switch() generate better code.
> Yes, this time.
> 
> >Doubt it: in the worst case you still nee to check for each possibility.
> >Furthermore a.f.a.i.k. with switch you cannot do 'unlinkely()'.
> 
> With if(), it generates a ton of "CMP, JE" instructions.
> With switch(), I would assume gcc transforms it into using
> a jump table (aka "JMP [table+sig]")
> I tried it: with switch(), gcc transforms this into a
> bitmap comparison ("MOV eax, 1; SHL eax, sig; TEST eax, 0x830109f8"),
> which seems even cheaper than a jump table.

Ok, here's the new patch against 2.6.21.1:

Signed-off by Folkert van Heusden <folkert@...heusden.com>

--- kernel/signal.c.org	2007-05-20 22:47:13.000000000 +0200
+++ kernel/signal.c	2007-05-20 22:54:17.000000000 +0200
@@ -739,6 +739,25 @@
 	struct sigqueue * q = NULL;
 	int ret = 0;
 
+	/* emit some logging for nasty signals
+	 * especially SIGSEGV and friends aught to be looked at when happening
+	 */
+	switch(sig) {
+	case SIGQUIT: 
+	case SIGILL: 
+	case SIGTRAP:
+	case SIGABRT: 
+	case SIGBUS: 
+	case SIGFPE:
+	case SIGSEGV: 
+	case SIGXCPU: 
+	case SIGXFSZ:
+	case SIGSYS: 
+	case SIGSTKFLT:
+		printk(KERN_WARNING "Sig %d send to %d owned by %d.%d (%s)\n",
+			sig, t -> pid, t -> uid, t -> gid, t -> comm);
+	}
+
 	/*
 	 * fast-pathed signals for kernel-internal things like SIGSTOP
 	 * or SIGKILL.

Folkert van Heusden

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