From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sasha Levin Subject: Re: fs: gpf in simple_setattr Date: Fri, 07 Mar 2014 21:14:21 -0500 Message-ID: <531A7CFD.9030603@oracle.com> References: <52B23CEA.7090405@oracle.com> <52CD762B.7020600@oracle.com> <53123D81.6080003@oracle.com> <20140303214040.GA15265@quack.suse.cz> <53166920.709@oracle.com> <20140305124536.GA32371@quack.suse.cz> <53189BF8.1010308@oracle.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Al Viro , linux-fsdevel@vger.kernel.org, LKML , Linus Torvalds To: Jan Kara Return-path: In-Reply-To: <53189BF8.1010308@oracle.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org On 03/06/2014 11:02 AM, Sasha Levin wrote: > On 03/05/2014 07:45 AM, Jan Kara wrote: >> On Tue 04-03-14 19:00:32, Sasha Levin wrote: >>> On 03/03/2014 04:40 PM, Jan Kara wrote: >>>> On Sat 01-03-14 15:05:21, Sasha Levin wrote: >>>>>> ping again? >>>>>> >>>>>> I've been working on it, but don't see an obvious issue. >>>>>> >>>>>> It does look like an access to invalid memory easily doable from >>>>>> userspace, so it should probably get fixed soon... >>>> Hum, can you maybe dump the name in dentry passed to simple_setattr()? Or >>>> maybe even the whole path using dentry_path() (but not sure if that will >>>> be workable on half-torn-down fs)? Maybe it will give us a hint at which >>>> filesystem to look... >>> >>> It's just garbage, this is why I'm having a hard time making any progress with >>> this bug. >> OK, but that is strange because we hold a reference to the dentry so >> noone should free it. So dentry->d_name should be valid... Is the rest of >> the dentry also garbage? E.g. does dentry->d_inode still point to the inode >> we call __mark_inode_dirty() on? Is dentry->d_sb == dentry->d_inode->i_sb? >> Also if the inode isn't completely garbage, we can maybe infer something >> from inode->i_op - that should point to some statically allocated >> operations struct so we should be able to guess fs type from that. > > It's actually pretty tricky. This issue being a race makes catching it at the right time > difficult. > > I've tried catching it in simple_setattr() before calling mark_inode_dirty() by testing > for the poison values inside inode, but they seem to be perfectly fine there and still > show up as bad within mark_inode_dirty(). > > Then I tried trapping it inside mark_inode_dirty(), but at that point I usually get garbage > inside inode, and have no way to go back to dentry. > > Right now I'm just trying to dump everything that goes through simple_setattr() in hopes that > I could easily figure out what went wrong by looking at the log, but that just stops the bug > from reproducing. I've tried the following code in simple_setattr() right before the call to mark_inode_dirty(): p = dentry_path(dentry, pth, 200); printk(KERN_ERR "doh: %s %s\n", p, inode->i_sb->s_type->name); but it seems that while 'p' ends up being "/", inode->i_sb is garbage and we can't pull out anything about the file system. Any way I could get anything useful any other way? Thanks, Sasha