Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752784AbZGAPiR (ORCPT ); Wed, 1 Jul 2009 11:38:17 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751491AbZGAPiD (ORCPT ); Wed, 1 Jul 2009 11:38:03 -0400 Received: from charlotte.tuxdriver.com ([70.61.120.58]:41566 "EHLO smtp.tuxdriver.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750894AbZGAPiB (ORCPT ); Wed, 1 Jul 2009 11:38:01 -0400 Date: Wed, 1 Jul 2009 11:37:57 -0400 From: Neil Horman To: linux-kernel@vger.kernel.org Cc: oleg@redhat.com, alan@lxorguk.ukuu.org.uk, andi@firstfloor.org, akpm@linux-foundation.org, earl_chew@agilent.com Subject: Re: [PATCH 3/3] exec: Allow do_coredump to wait for user space pipe readers to complete (v5) Message-ID: <20090701153757.GG29601@hmsreliant.think-freely.org> References: <20090622172818.GB14673@hmsreliant.think-freely.org> <20090701152640.GD29601@hmsreliant.think-freely.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090701152640.GD29601@hmsreliant.think-freely.org> User-Agent: Mutt/1.5.18 (2008-05-17) X-Spam-Score: -1.4 (-) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2993 Lines: 87 core_pattern: Allow core_pattern pipes to wait for user space to complete One of the things that user space processes like to do is look at metadata for a crashing process in their /proc/ directory. this is racy however, since do_coredump in the kernel doesn't wait for the user space process to complete before it reaps the crashing process. This patch corrects that. Allowing the kernel to wait for the user space process to complete before cleaning up the crashing process. This is a bit tricky to do for a few reasons: 1) The user space process isn't our child, so we can't sys_wait4 on it 2) We need to close the pipe before waiting for the user process to complete, since the user process may rely on an EOF condition I've discussed several solutions with Oleg Nesterov off-list about this, and this is the one we've come up with. We basically add ourselves as an additional reader (to prevent cleanup of the pipe), write the dump in ->core_dump(), then iteratively remove ourselves as a writer (to create the EOF condition) and wake up the user process. note that we add ourselves as a reader before writing the file. this closes the race in the window between the time we write the dump and the time we start checking for the user space process to be done with the pipe. Signed-off-by: Neil Horman Reported-by: Earl Chew exec.c | 29 +++++++++++++++++++++++++++++ 1 file changed, 29 insertions(+) diff --git a/fs/exec.c b/fs/exec.c index 93ab6eb..d124346 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -55,6 +55,7 @@ #include #include #include +#include #include #include @@ -1711,6 +1712,32 @@ int get_dumpable(struct mm_struct *mm) return (ret >= 2) ? 2 : ret; } +static void wait_for_dump_helpers(struct file *file) +{ + struct pipe_inode_info *pipe; + + pipe = file->f_path.dentry->d_inode->i_pipe; + + pipe_lock(pipe); + pipe->readers++; + pipe->writers--; + while (pipe->readers > 1) { + wake_up_interruptible_sync(&pipe->wait); + kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN); + pipe_wait(pipe); + } + + /* + * This reclaims the additional readers count we took in + * do_coredump + */ + pipe->readers--; + pipe->writers++; + pipe_unlock(pipe); + +} + + void do_coredump(long signr, int exit_code, struct pt_regs *regs) { struct core_state core_state; @@ -1862,6 +1889,8 @@ void do_coredump(long signr, int exit_code, struct pt_regs *regs) current->signal->group_exit_code |= 0x80; close_fail: + if (ispipe && core_pipe_limit) + wait_for_dump_helpers(file); filp_close(file, NULL); fail_dropcount: if (dump_count) -- 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/