From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751047AbVHaUBX (ORCPT ); Wed, 31 Aug 2005 16:01:23 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751074AbVHaUBX (ORCPT ); Wed, 31 Aug 2005 16:01:23 -0400 Received: from e1.ny.us.ibm.com ([32.97.182.141]:9949 "EHLO e1.ny.us.ibm.com") by vger.kernel.org with ESMTP id S1751046AbVHaUBW (ORCPT ); Wed, 31 Aug 2005 16:01:22 -0400 Date: Wed, 31 Aug 2005 13:01:09 -0700 From: Nishanth Aravamudan To: akpm@osdl.org Cc: dwmw2@infradead.org, bunk@stusta.de, johnstul@us.ibm.com, drepper@redhat.com, Franz.Fischer@goyellow.de, LKML Subject: [PATCH][Bug 5132] fix sys_poll() large timeout handling Message-ID: <20050831200109.GB3017@us.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.9i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Sorry everybody, forgot the most important Cc: :) -Nish Hi Andrew, In looking at Bug 5132 and sys_poll(), I think there is a flaw in the current code. The @timeout parameter to sys_poll() is in milliseconds but we compare it to (MAX_SCHEDULE_TIMEOUT / HZ), which is jiffies/jiffies-per-sec or seconds. That seems blatantly broken. Also, I think we are better served by converting to jiffies first then comparing, as opposed to converting our maximum to milliseconds (or seconds, incorrectly) and comparing. Comments, suggestions for improvement? Description: The current sys_poll() implementation does not seem to handle large timeouts correctly. Any value in milliseconds (@timeout) which exceeds the maximum representable jiffy value (MAX_SCHEDULE_TIMEOUT) should result in a MAX_SCHEDULE_TIMEOUT schedule_timeout() call. To achieve this, convert @timeout to jiffies first, then compare to MAX_SCHEDULE_TIMEOUT. Signed-off-by: Nishanth Aravamudan --- fs/select.c | 14 +++++++++----- 1 files changed, 9 insertions(+), 5 deletions(-) diff -urpN 2.6.13/fs/select.c 2.6.13-dev/fs/select.c --- 2.6.13/fs/select.c 2005-08-28 17:46:14.000000000 -0700 +++ 2.6.13-dev/fs/select.c 2005-08-31 12:43:52.000000000 -0700 @@ -470,12 +470,16 @@ asmlinkage long sys_poll(struct pollfd _ return -EINVAL; if (timeout) { - /* Careful about overflow in the intermediate values */ - if ((unsigned long) timeout < MAX_SCHEDULE_TIMEOUT / HZ) - timeout = (unsigned long)(timeout*HZ+999)/1000+1; - else /* Negative or overflow */ - timeout = MAX_SCHEDULE_TIMEOUT; + /* + * Convert the value from msecs to jiffies - if overflow + * occurs we get a negative value, which gets handled by + * the next block + */ + timeout = msecs_to_jiffies(timeout) + 1; } + if (timeout < 0) /* Negative requests result in infinite timeouts */ + timeout = MAX_SCHEDULE_TIMEOUT; + /* 0 case falls through */ poll_initwait(&table);