Path: news.gmane.org!not-for-mail From: Evgeniy Polyakov Newsgroups: gmane.linux.network,gmane.linux.kernel.announce Subject: Re: kmap_atomic() oopses in current mainline Date: Thu, 19 Jul 2007 14:01:33 +0400 Lines: 60 Approved: news@gmane.org Message-ID: <20070719100132.GC15839@2ka.mipt.ru> References: <20070719013304.3c060c99.akpm@linux-foundation.org> <20070719092856.GA15839@2ka.mipt.ru> <20070719023831.400f7905.akpm@linux-foundation.org> NNTP-Posting-Host: lo.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset=koi8-r X-Trace: sea.gmane.org 1184839406 11897 80.91.229.12 (19 Jul 2007 10:03:26 GMT) X-Complaints-To: usenet@sea.gmane.org NNTP-Posting-Date: Thu, 19 Jul 2007 10:03:26 +0000 (UTC) Cc: netdev@vger.kernel.org, linux-kernel-announce@vger.kernel.org, Dan Williams To: Andrew Morton Original-X-From: netdev-owner@vger.kernel.org Thu Jul 19 12:03:24 2007 Return-path: Envelope-to: linux-netdev-2@gmane.org Original-Received: from vger.kernel.org ([209.132.176.167]) by lo.gmane.org with esmtp (Exim 4.50) id 1IBSqv-0004K5-VQ for linux-netdev-2@gmane.org; Thu, 19 Jul 2007 12:03:22 +0200 Original-Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1765535AbXGSKCg (ORCPT ); Thu, 19 Jul 2007 06:02:36 -0400 Original-Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1765485AbXGSKCf (ORCPT ); Thu, 19 Jul 2007 06:02:35 -0400 Original-Received: from relay.2ka.mipt.ru ([194.85.82.65]:35936 "EHLO 2ka.mipt.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932085AbXGSKCe (ORCPT ); Thu, 19 Jul 2007 06:02:34 -0400 Original-Received: from 2ka.mipt.ru (localhost [127.0.0.1]) by 2ka.mipt.ru (8.14.1/8.14.1) with ESMTP id l6JA1Y7W022308; Thu, 19 Jul 2007 14:01:34 +0400 Original-Received: (from johnpol@localhost) by 2ka.mipt.ru (8.14.1/8.12.1/Submit) id l6JA1Xek022304; Thu, 19 Jul 2007 14:01:33 +0400 Content-Disposition: inline In-Reply-To: <20070719023831.400f7905.akpm@linux-foundation.org> User-Agent: Mutt/1.5.9i Original-Sender: netdev-owner@vger.kernel.org Precedence: bulk X-Mailing-List: netdev@vger.kernel.org Xref: news.gmane.org gmane.linux.network:66991 gmane.linux.kernel.announce:461 On Thu, Jul 19, 2007 at 02:38:31AM -0700, Andrew Morton (akpm@linux-foundation.org) wrote: > > > is very wrong if both ASYNC_TX_KMAP_DST and ASYNC_TX_KMAP_SRC can ever be > > > set. We'll end up using the same kmap slot for both src add dest and we > > > get either corrupted data or a BUG. > > > > So far it can not since the only user is raid code, which only allows to > > perform either reading from bio or writing into one, which requires only > > one mapping. > > hm, so we got lucky? I would say it was intentionally, current code can perform only one operation in a time. Of course changing KM_USER from 0 to 1 in second kmap_atomic will not force oceans to run out of coasts. Kind of: diff --git a/crypto/async_tx/async_memcpy.c b/crypto/async_tx/async_memcpy.c index a973f4e..a48c7f3 100644 --- a/crypto/async_tx/async_memcpy.c +++ b/crypto/async_tx/async_memcpy.c @@ -94,7 +94,7 @@ async_memcpy(struct page *dest, struct page *src, unsigned int dest_offset, dest_buf = page_address(dest) + dest_offset; if (flags & ASYNC_TX_KMAP_SRC) - src_buf = kmap_atomic(src, KM_USER0) + src_offset; + src_buf = kmap_atomic(src, KM_USER1) + src_offset; else src_buf = page_address(src) + src_offset; @@ -104,7 +104,7 @@ async_memcpy(struct page *dest, struct page *src, unsigned int dest_offset, kunmap_atomic(dest_buf, KM_USER0); if (flags & ASYNC_TX_KMAP_SRC) - kunmap_atomic(src_buf, KM_USER0); + kunmap_atomic(src_buf, KM_USER1); async_tx_sync_epilog(flags, depend_tx, cb_fn, cb_param); } > > Btw, shouldn't it always be kmap_atomic() even if flag is not set. > > That pages are usual one returned by alloc_page(). > > The code would work OK if the kmap_atomic()s were unconditional, but it > would be a bit more expensive if the page is in highmem and we don't > actually intend to access it with the CPU. > > kmap_atomic() against a non-highmem page is basically free: just an > additional test_bit(). As far as I recall there was an intention to do async memory copy to userspace, so likely kmapping is a good idea. -- Evgeniy Polyakov - To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html