Messages in this thread | | | Date | Wed, 4 Jan 2006 01:36:58 -0800 | From | Andrew Morton <> | Subject | Re: [PATCH] protect remove_proc_entry |
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Kirill Korotaev <dev@sw.ru> wrote: > > Hi Andrew, > > I have a full patch for this.
Please don't top-post. It makes things hard...
> I don't remember the details yet, but lock was not god here, we used > semaphore. I pointed to this problem long ago when fixed error path in > proc with moduleget. > > This patch protects proc_dir_entry tree with a proc_tree_sem semaphore. > I suppose lock_kernel() can be removed later after checking that no proc > handlers require it. > Also this patch remakes de refcounters a bit making it more clear and > more similar to dentry scheme - this is required to make sure that > everything works correctly. > > Patch is against 2.6.15-rcX and was tested for about a week. Also works > half a year on 2.6.8 :) > > [ patch which uses an rwsem for procfs and somewhat removes lock_kernel() ] >
I worry about replacing a spinlock with a sleeping lock. In some circumstances it can cause a complete scalability collapse and I suspect this could happen with /proc. Although I guess the only fastpath here is proc_readdir(), and as the lock is taken there for reading, we'll be OK..
The patch does leave some lock_kernel() calls behind. If we're going to do this, I think they should all be removed?
Races in /proc have been plentiful and hard to find. The patch worries me, frankly. I'd like to see quite a bit more description of the locking schema and some demonstration that it's actually complete before taking the plunge.
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