From linux-kernel-owner+willy=40w.ods.org@vger.kernel.org Wed Mar 12 23:20:50 2003 Return-Path: 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 ; 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 ; Wed, 12 Mar 2003 23:20:51 +0100 (CET) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Wed, 12 Mar 2003 17:03:23 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; 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 ; 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/