From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759470AbZJKMRz (ORCPT ); Sun, 11 Oct 2009 08:17:55 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756525AbZJKMRy (ORCPT ); Sun, 11 Oct 2009 08:17:54 -0400 Received: from mail-ew0-f208.google.com ([209.85.219.208]:47536 "EHLO mail-ew0-f208.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753832AbZJKMRx convert rfc822-to-8bit (ORCPT ); Sun, 11 Oct 2009 08:17:53 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type:content-transfer-encoding; b=bkzET54fMDXFz/iEY77fSEpCx0ZObfRwzbazUgOLXmBswetAUIqLqmHjTmt2A3J7q4 8kbvcqZXVzS1cIMUXsktv6M10K7SA2ICYIUgfmgdgmFeI6bFXoLxK03rlNRLZO9XmEwl Hd+wJDoEStk2NoKq3ZpdZIU942Uqfq+hP5VXk= MIME-Version: 1.0 In-Reply-To: <28675.1248957636@turing-police.cc.vt.edu> References: <1244461122-3303-1-git-send-email-alexander.shishckin@gmail.com> <71a0d6ff0907290917u1f0c0e68p8036d53c69320392@mail.gmail.com> <28675.1248957636@turing-police.cc.vt.edu> Date: Sun, 11 Oct 2009 15:17:42 +0300 Message-ID: <71a0d6ff0910110517v1068d7cyd8bb076abab23ed5@mail.gmail.com> Subject: Re: [PATCH] [RFC] List per-process file descriptor consumption when hitting file-max From: Alexander Shishkin To: Valdis.Kletnieks@vt.edu Cc: linux-fsdevel@vger.kernel.org, akpm@linux-foundation.org, viro@zeniv.linux.org.uk, Linux Kernel Mailing List Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 2009/7/30 : > On Wed, 29 Jul 2009 19:17:00 +0300, Alexander Shishkin said: >>Is there anything dramatically wrong with this one, or could someone please review this? > > >> +               for_each_process(p) { >> +                       files = get_files_struct(p); >> +                       if (!files) >> +                               continue; >> + >> +                       spin_lock(&files->file_lock); >> +                       fdt = files_fdtable(files); >> + >> +                       /* we have to actually *count* the fds */ >> +                       for (count = i = 0; i < fdt->max_fds; i++) >> +                               count += !!fcheck_files(files, i); >> + >> +                       printk(KERN_INFO "=> %s [%d]: %d\n", p->comm, >> +                                       p->pid, count); > > 1) Splatting out 'count' without a hint of what it is isn't very user friendly. > Consider something like "=> %s[%d]: open=%d\n" instead, or add a second line > to the 'VFS: file-max' printk to provide a header. Fair enough. > 2) What context does this run in, and what locks/scheduling considerations > are there? On a large system with many processes running, this could conceivably > wrap the logmsg buffer before syslog has a chance to get scheduled and read > the stuff out. That's a good point. > 3) This can be used by a miscreant to spam the logs - consider a program > that does open() until it hits the limit, then goes into a close()/open() > loop to repeatedly bang up against the limit. Every 2 syscalls by the > abuser could get them another 5,000+ lines in the log - an incredible > amplification factor. > > Now, if you fixed it to only print out the top 10 offending processes, it would > make it a lot more useful to the sysadmin, and a lot of those considerations go > away, but it also makes the already N**2 behavior even more expensive... That's a good idea. I think some kind of rate-limiting can be applied here too. > At that point, it would be good to report some CPU numbers by running a abusive > program that repeatedly hit the limit, and be able to say "Even under full > stress, it only used 15% of a CPU on a 2.4Ghz Core2" or similar... I'll see what I can do. Thanks for your comments and ideas! Regards, -- Alex