Date: Thu, 15 Jan 2015 05:31:09 +0200 From: Konstantin Belousov <kostikbel@gmail.com> To: Hans Petter Selasky <hselasky@FreeBSD.org> Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org, src-committers@freebsd.org Subject: Re: svn commit: r277199 - in head/sys: fs/devfs kern Message-ID: <20150115033109.GM42409@kib.kiev.ua> In-Reply-To: <201501142207.t0EM7Dfn041543@svn.freebsd.org> References: <201501142207.t0EM7Dfn041543@svn.freebsd.org>
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On Wed, Jan 14, 2015 at 10:07:13PM +0000, Hans Petter Selasky wrote: > Author: hselasky > Date: Wed Jan 14 22:07:13 2015 > New Revision: 277199 > URL: https://svnweb.freebsd.org/changeset/base/277199 > > Log: > Avoid race with "dev_rel()" when using the recently added > "delist_dev()" function. Make sure the character device structure > doesn't go away until the end of the "destroy_dev()" function due to > concurrently running cleanup code inside "devfs_populate()". > > MFC after: 1 week > Reported by: dchagin@ > > Modified: > head/sys/fs/devfs/devfs_devs.c > head/sys/kern/kern_conf.c > > Modified: head/sys/fs/devfs/devfs_devs.c > ============================================================================== > --- head/sys/fs/devfs/devfs_devs.c Wed Jan 14 22:05:57 2015 (r277198) > +++ head/sys/fs/devfs/devfs_devs.c Wed Jan 14 22:07:13 2015 (r277199) > @@ -137,6 +137,12 @@ devfs_alloc(int flags) > vfs_timestamp(&ts); > cdev->si_atime = cdev->si_mtime = cdev->si_ctime = ts; > cdev->si_cred = NULL; > + /* > + * Avoid race with dev_rel() by setting the initial > + * reference count to 1. This last reference is taken > + * by the destroy_dev() function. > + */ > + cdev->si_refcount = 1; This is wrong. Not all devices are destroyed with destroy_dev(). dev_rel() must be allowed to clean up allocated device. That said, I do not understand what race you are trying to solve. Freeing of the accessible cdev memory cannot happen in parallel while dev_mtx is owned. Please do not commit (to devfs) without seeking for the review first. > > return (cdev); > } > > Modified: head/sys/kern/kern_conf.c > ============================================================================== > --- head/sys/kern/kern_conf.c Wed Jan 14 22:05:57 2015 (r277198) > +++ head/sys/kern/kern_conf.c Wed Jan 14 22:07:13 2015 (r277199) > @@ -1048,8 +1048,6 @@ destroy_devl(struct cdev *dev) > /* Remove name marking */ > dev->si_flags &= ~SI_NAMED; > > - dev->si_refcount++; /* Avoid race with dev_rel() */ > - > /* If we are a child, remove us from the parents list */ > if (dev->si_flags & SI_CHILD) { > LIST_REMOVE(dev, si_siblings);
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