Messages in this thread | | | Date | Wed, 30 Oct 2013 09:28:31 -0400 | From | Tejun Heo <> | Subject | Re: [PATCH] sysfs: move assignment to be under lock in sysfs_remove_dir() |
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Hello,
On Tue, Oct 29, 2013 at 10:29:43PM -0700, Eric W. Biederman wrote: > I never actually looked deeply into it, and I was working from several > year old memory and a quick skim of the patch when I asked the question. > > The protection we have previous to this patch is that syfs_remove_dir is > only sane to call once. > > Which makes the code that does: > if (!dir_sd) > return; > in __sysfs_remove_dir very suspicious. I expect we want a > WARN_ON(!dir_sd);
It was always like that, probably in the same spirit as kfree() taking NULL so that it can be easier, for example, in init failure paths.
> But the entire directory removal process and working on sysfs stopped > being fun before I managed to get that cleaned up. And unless I missed > something go by Tejun is going to go generalize this thing before this > bit gets cleaned up. Sigh.
I kept the same behavior for kernfs_remove(). I don't think it's something we explicitly want to clean up tho? It's an acceptable behavior.
> On an equally bizarre note. I don't understand why we have a separate > spinlock there. Looks... Sigh. We use a different lock from > everything as a premature optimization so that sysfs_remove_dir could be > modified to just take a sysfs_dirent, and all of the kobject handling > could be removed. > > Sigh. It was never in my way and while I was working on the code that > there was a good locking reason for doing that silly thing.
Umm... you got it completely wrong. It's there to address a race condition between removal and symlinking and has nothing to do with optimization.
The current odd looking locking on removal side serves a purpose in making it clear that it isn't synchronizing concurrent removal calls. Maybe we should rename the lock to sysfs_symlink_target_lock and add fat comments on both sides? Or we can make it a mutex and exclude the entire removal and symlinking, which would probably easier to follow.
Thanks.
-- tejun
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