Messages in this thread | | | Date | Fri, 26 Jul 2013 09:38:56 -0400 | From | Tejun Heo <> | Subject | Re: [PATCH] race condition fixing in sysfs_create_dir |
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Hello,
On Fri, Jul 26, 2013 at 05:59:00PM +0800, Dennis Chen wrote: > On 07/26/2013 05:49 PM, Dennis Chen wrote: > > >The patch is trying its best to avoid creating a dir under a parent dir which is removing from > >the system: > > PATH0 (create a dir under 'PARENT/...') PATH1 (remove the 'PARENT/...') > > sysfs_create_dir() { sysfs_remove_dir() { > > ... ... > > if (kobj->parent) spin_lock(&sysfs_assoc_lock); > > parent_sd = kobj->parent->sd; <----- kobj->sd = NULL; > > else spin_unlock(&sysfs_assoc_lock); > > parent_sd = &sysfs_root; > >Suppose PATH1 enter the critical section first, then PATH0 begin to execute before kobj->sd > >has been reset to NULL, possibly PATH0 will get a non-NULL parent_sd since lack of the > >sysfs_assoc_lock protection in PATH0. In this case, PATH0 think it has a valid parent_sd which > >can be freed by PATH1 in the followed, refer to the comments in the patch. Maybe we need > >to figure out a perfect solution to solve the race condition, although the codes in question are > >in slow path...
I don't think sysfs is supposed to handle multiple actors trying to populate and destroy the directory at the same time at all, so this seems kinda moot. Do you have a case where this actually matters?
Thanks.
-- tejun
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