Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Thu, 13 Mar 2003 04:15:07 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Thu, 13 Mar 2003 04:15:07 -0500 Received: from ns.virtualhost.dk ([195.184.98.160]:19637 "EHLO virtualhost.dk") by vger.kernel.org with ESMTP id ; Thu, 13 Mar 2003 04:15:06 -0500 Date: Thu, 13 Mar 2003 10:26:01 +0100 From: Jens Axboe To: Joe Korty Cc: Alan Cox , linux-kernel@vger.kernel.org Subject: Re: [PATCH] bug in 2.4 bh_kmap_irq() breaks IDE under preempt patch Message-ID: <20030313092601.GB827@suse.de> References: <200303122213.WAA17415@rudolph.ccur.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <200303122213.WAA17415@rudolph.ccur.com> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2260 Lines: 70 On Wed, Mar 12 2003, Joe Korty wrote: > 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. I fixed this in 2.5 ages ago, just didn't get it in 2.4 block-highmem... There's a tiny bit missing from your patch: > --- include/linux/highmem.h.orig 2003-03-12 05:01:56.000000000 -0500 > +++ 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); local_irq_disable(); > 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); > } other than that it's fine. See 2.5 for reference. -- Jens Axboe - 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/