Re: [PATCH] vfs: Fix possible NULL pointer dereference ininode_permission()

[Al Viro]

On Thu, Jan 09, 2014 at 04:50:12PM -0500, Steven Rostedt wrote:

> > We'd then have to get rid of all the call_rcu() invocations in individual
> > filesystems' destroy_inode methods, but that doesn't sound like a bad
> > thing to me.

Check what e.g. XFS is doing...

> Which is another reason that I didn't do it, as I didn't know all the
> happenings inside the ->destroy_inode() calls. But yeah, I agree with
> this.
> 
> Also, can iput() sleep? If not then we are OK. Otherwise, we need to be
> careful about any mutex being grabbed in those call backs, as the
> rcu_callback can't sleep either.

iput() definitely can sleep (that's when actual truncation and inode
freeing is done for opened-and-unlinked files - on the final iput() after
close()), but that' irrelevant here - fsnotify_delete_inode() grabs
a bunch of mutexes, which makes calling it from rcu callback no-go.
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