From linux-kernel-owner+willy=40w.ods.org@vger.kernel.org Wed Mar 12 23:20:50 2003
Return-Path: <linux-kernel-owner+willy=40w.ods.org@vger.kernel.org>
Received: from vax.home.local (vax [10.2.1.2])
by alpha.home.local (8.12.4/8.12.1) with ESMTP id h2CMKoN1019696
for <willy@w.ods.org>; Wed, 12 Mar 2003 23:20:50 +0100
Received: from vger.kernel.org (vger.kernel.org [209.116.70.75])
by vax.home.local (8.12.2/8.12.1) with ESMTP id h2CMKj1R006506
for <willy@w.ods.org>; Wed, 12 Mar 2003 23:20:51 +0100 (CET)
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
id <S261999AbTCLWDX>; Wed, 12 Mar 2003 17:03:23 -0500
Received: (majordomo@vger.kernel.org) by vger.kernel.org
id <S262000AbTCLWDX>; Wed, 12 Mar 2003 17:03:23 -0500
Received: from users.ccur.com ([208.248.32.211]:55303 "HELO rudolph.ccur.com")
by vger.kernel.org with SMTP id <S261999AbTCLWDV>;
Wed, 12 Mar 2003 17:03:21 -0500
Received: by rudolph.ccur.com (8.6.10/CCC-4.1)
id WAA17415; Wed, 12 Mar 2003 22:13:47 GMT
From: jak@rudolph.ccur.com (Joe Korty)
Message-Id: <200303122213.WAA17415@rudolph.ccur.com>
Subject: [PATCH] bug in 2.4 bh_kmap_irq() breaks IDE under preempt patch
To: alan@lxorguk.ukuu.org.uk (Alan Cox)
Date: Wed, 12 Mar 2003 17:13:47 -0500 (EST)
Cc: linux-kernel@vger.kernel.org
Reply-To: joe.korty@ccur.com (Joe Korty)
X-Mailer: ELM [version 2.5 PL0b1]
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk
X-Mailing-List: linux-kernel@vger.kernel.org
Status: RO
Content-Length: 1947
Lines: 65
Hi Alan, Everyone,
The bh_map_irq/bh_unmap_irq functions are broken in 2.4.21-pre5.
However no symptoms occur unless the preemption patch is applied.
The bug is that bh_map_irq *conditionally* calls kmap_atomic (which
disables preemption as one of its functions), while bh_unmap_irq
*unconditionally* calls kunmap_atomic (which enables it). This
imbalance results in a occasional off-by-one preempt_count, which in
turn causes IDE PIO mode interrupt code (specifically, read_intr) to
erronously invoke preempt_schedule while at interrupt level.
The below patch compiles and boots ide=nodma on my preempt 2.4 kernel
on the one motherboard that had the problem. Before this patch, the
kernel would not even boot for that motherboard. I also applied and
test booted a pure 2.4.21-pre5 kernel with this patch.
The patch implements my preference for simplicity, so you may want to
take some other approach if maximal performance is what you want.
Joe
--- old/include/linux/highmem.h.orig 2003-03-12 05:01:56.000000000 -0500
+++ new/include/linux/highmem.h 2003-03-12 16:07:04.000000000 -0500
@@ -33,22 +33,10 @@
{
unsigned long addr;
- __save_flags(*flags);
-
- /*
- * could be low
- */
- if (!PageHighMem(bh->b_page))
- return bh->b_data;
-
- /*
- * it's a highmem page
- */
- __cli();
+ local_irq_save(*flags);
addr = (unsigned long) kmap_atomic(bh->b_page, KM_BH_IRQ);
- if (addr & ~PAGE_MASK)
- BUG();
+ BUG_ON (addr & ~PAGE_MASK);
return (char *) addr + bh_offset(bh);
}
@@ -58,7 +46,7 @@
unsigned long ptr = (unsigned long) buffer & PAGE_MASK;
kunmap_atomic((void *) ptr, KM_BH_IRQ);
- __restore_flags(*flags);
+ local_irq_restore(*flags);
}
#else /* CONFIG_HIGHMEM */
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/