linux-kernel - PATCH - x86-64 signed-compare bug, was Re: select() setting ERESTARTNOHAND (514).

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Message-ID: <17829.34481.340913.519675@notabene.brown>
Date:	Thu, 11 Jan 2007 11:37:05 +1100
From:	Neil Brown <neilb@...e.de>
To:	Sean Reifschneider <jafo@...my.com>
Cc:	linux-kernel@...r.kernel.org, ak@...e.de
Subject: PATCH - x86-64 signed-compare bug, was Re: select() setting ERESTARTNOHAND (514).

On Wednesday January 10, jafo@...my.com wrote:
> 
> In looking at the Linux code for ERESTARTNOHAND, I see that
> include/linux/errno.h says this errno should never make it to the user.
> However, in this instance we ARE seeing it.  Looking around on google shows
> others are seeing it as well, though hits are few.
..
> 
> Thoughts?

Just a 'me too' at this point. 
The X server on my shiny new notebook (Core 2 Duo) occasionally dies
with 'select' repeatedly returning ERESTARTNOHAND.  It is most
annoying!

You don't mention in the Email which kernel version you use but I see
from the web page you reference it is 2.6.19.1.  I'm using
2.6.18.something.

I thought I'd have a quick look at the code, comparing i386 to x86-64
and guess what I found.....

On x86-64, regs->rax is "unsigned long", so the following is
needed....

I haven't tried it yet.

NeilBrown

Signed-off-by: Neil Brown <neilb@...e.de>

### Diffstat output
 ./arch/x86_64/kernel/signal.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff .prev/arch/x86_64/kernel/signal.c ./arch/x86_64/kernel/signal.c
--- .prev/arch/x86_64/kernel/signal.c	2007-01-11 11:33:27.000000000 +1100
+++ ./arch/x86_64/kernel/signal.c	2007-01-11 11:34:01.000000000 +1100
@@ -331,7 +331,7 @@ handle_signal(unsigned long sig, siginfo
 	/* Are we from a system call? */
 	if ((long)regs->orig_rax >= 0) {
 		/* If so, check system call restarting.. */
-		switch (regs->rax) {
+		switch ((long)regs->rax) {
 		        case -ERESTART_RESTARTBLOCK:
 			case -ERESTARTNOHAND:
 				regs->rax = -EINTR;
-
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