Return-Path: Message-ID: <477F9481.2040505@gmail.com> Date: Sat, 05 Jan 2008 23:30:25 +0900 From: Tejun Heo MIME-Version: 1.0 To: Al Viro References: <20071228173203.GA20690@boogie.lpds.sztaki.hu> <20080102151642.GA7273@boogie.lpds.sztaki.hu> <20080105075039.GF27894@ZenIV.linux.org.uk> In-Reply-To: <20080105075039.GF27894@ZenIV.linux.org.uk> Cc: Greg KH , Gabor Gombas , bluez-devel@lists.sf.net, linux-kernel@vger.kernel.org Subject: Re: [Bluez-devel] Oops involving RFCOMM and sysfs Reply-To: BlueZ development List-Id: BlueZ development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Sender: bluez-devel-bounces@lists.sourceforge.net Errors-To: bluez-devel-bounces@lists.sourceforge.net Hello. Al Viro wrote: > sysfs_get_dentry(), > mutex_lock(&parent->d_inode->i_mutex); > hitting parent->d_inode either NULL or very close to it, depending on your > .config; most likely NULL, if offset of i_mutex is 0xb8 in your build. > That's plausible - 0xb8 is what you'd get on UP build without spinlock > debugging, lockdep, etc. > > Assuming that this is what we get, everything looks explainable - we > have sysfs_rename_dir() calling sysfs_get_dentry() while the parent > gets evicted. We don't have any exclusion, so while we are playing > silly buggers with lookups in sysfs_get_dentry() we have parent become > negative; the rest is obvious... That part of code is walking down the sysfs tree from the s_root of sysfs hierarchy and on each step parent is held using dget() while being referenced, so I don't think they can turn negative there. > AFAICS, the locking here is quite broken and frankly, sysfs_get_dentry() > and the way it plays with fs/namei.c are ucking fugly. Can you elaborate a bit? The locking in sysfs is unconventional but that's mostly from necessity. It has dual interface - vfs and driver model && vfs data structures (dentry and inode) are too big to always keep around, so it basically becomes a small distributed file system where the backing data can change asynchronously. > Could you stick > if (!parent->d_inode) > printk(KERN_WARNING "sysfs locking blows: %s", > parent->d_name.name); > right before > mutex_lock(&parent->d_inode->i_mutex); > dentry = lookup_one_noperm(cur->s_name, parent); > mutex_unlock(&parent->d_inode->i_mutex); > in sysfs_get_dentry() (fs/sysfs/dir.c) and verify that it does, indeed, > trigger? Yes, please. Thanks. -- tejun ------------------------------------------------------------------------- This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2005. http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ _______________________________________________ Bluez-devel mailing list Bluez-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/bluez-devel