lkml.org 
[lkml]   [2010]   [Dec]   [1]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH v2 3/3] NFS: Fix a memory leak in nfs_readdir
On Wed, 1 Dec 2010, Linus Torvalds wrote:
> On Wed, Dec 1, 2010 at 2:13 PM, Andrew Morton <akpm@linux-foundation.org> wrote:
> > On Wed, 01 Dec 2010 16:51:12 -0500
> > Trond Myklebust <Trond.Myklebust@netapp.com> wrote:
> >
> >> On Wed, 2010-12-01 at 13:38 -0800, Andrew Morton wrote:
> >> > Probably on most call paths we'll be OK - if a process is in the middle
> >> > of a file truncate, holdin a file* ref which holds an inode ref then
> >> > nobody will be unmounting that fs and hence nobody will be unloading
> >> > that module.
> >> >
> >> > However on the random_code->alloc_page->vmscan->releasepage path, none
> >> > of that applies.
> >>
> >> Just out of interest, what ensures that the mapping is still around for
> >> the 'spin_unlock_irq(&mapping->tree_lock);' in __remove_mapping()?
> >
> > Nothing, afacit.
>
> No, we're good.
>
> Module unload has to go through a "stop_machine()" cycle, and that in
> turn requires an idle period for everything. And just a preemption
> reschedule isn't enough for that.
>
> So what is sufficient is that
>
> - we had the page locked and on the mapping
>
> This implies that we had an inode reference to the module, and the
> page lock means that the inode reference cannot go away (because it
> will involve invalidate-pages etc)

I'm not so sure of that: doesn't it test inode->i_data.nrpages in
various places, and skip ahead if that is already 0? I don't see
the necessary serialization when nrpages comes down to 0.

>
> - we're not sleeping after __remove_mapping, so unload can't happen afterwards.
>
> A _lot_ of the module races depend on that latter thing. We have
> almost no cases that are strictly about actual reference counts etc.

Okay, I'm reassured on my module unload point; but not on the
question of safety of spin_unlock_irq(&mapping->tree_lock)
which Trond lobbed back in return.

Hugh


\
 
 \ /
  Last update: 2010-12-01 23:47    [W:0.206 / U:0.444 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site