Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932652AbVIJAfe (ORCPT ); Fri, 9 Sep 2005 20:35:34 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932657AbVIJAfe (ORCPT ); Fri, 9 Sep 2005 20:35:34 -0400 Received: from e31.co.us.ibm.com ([32.97.110.129]:41669 "EHLO e31.co.us.ibm.com") by vger.kernel.org with ESMTP id S932652AbVIJAfc (ORCPT ); Fri, 9 Sep 2005 20:35:32 -0400 Date: Fri, 9 Sep 2005 17:35:25 -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: [UPDATE PATCH][Bug 5132] fix sys_poll() large timeout handling Message-ID: <20050910003525.GC24225@us.ibm.com> References: <20050831200109.GB3017@us.ibm.com> <20050906212514.GB3038@us.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20050906212514.GB3038@us.ibm.com> X-Operating-System: Linux 2.6.13 (i686) User-Agent: Mutt/1.5.10i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2858 Lines: 83 On 06.09.2005 [14:25:14 -0700], Nishanth Aravamudan wrote: > On 31.08.2005 [13:01:09 -0700], Nishanth Aravamudan wrote: > > 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? > > I haven't got any responses (here or on the bug)... A silent NACK? > Anything I should change to make people happier? Well, I found one thing to change. msecs_to_jiffies() deals in unsigned quantities while the parameter we are passing in is signed (and with reason). I mistakenly left the if (timeout) check in, when it should be if (timeout > 0) check. Fixed below. Thanks, Nish 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() request. To achieve this, convert @timeout to jiffies first, then compare to MAX_SCHEDULE_TIMEOUT. Signed-off-by: Nishanth Aravamudan --- fs/select.c | 17 ++++++++++------- 1 file changed, 10 insertions(+), 7 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 2005-09-09 17:22:30.000000000 -0700 @@ -469,13 +469,16 @@ asmlinkage long sys_poll(struct pollfd _ if (nfds > current->files->max_fdset && nfds > OPEN_MAX) 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; - } + if (timeout > 0) + /* + * 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); - 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/