Re: 2.6.0-test9 and sleeping function called from invalid context

[Andrew Morton <akpm@osdl.org>]

viro@parcelfarce.linux.theplanet.co.uk wrote:
>
> On Sat, Oct 25, 2003 at 10:49:50PM -0700, Andrew Morton wrote:
> > Andrew Morton <akpm@osdl.org> wrote:
> > >
> > > but the wider question would be: is the SELinux
> > >  d_instantiate callout allowed to sleep?  A quick audit seems to indicate
> > >  that it's OK, but only by luck I think.
> > 
> > proc_pid_lookup() calls d_add->d_instantiate under task->proc_lock, so
> > inode_doinit_with_dentry() is called under spinlock on this path as well.
> > 
> > Manfred, is there any particular reason why proc_pid_lookup()'s d_add is
> > inside the lock?
> 
> AFAICS, we can move d_add() right before taking the spinlock.  It's there
> to protect the ->proc_dentry assignment.

In which case we don't need to take the lock at all.  Two instances.

What protects against concurrent execution of proc_pid_lookup() and
proc_task_lookup()?  I think nothing, because one is at /proc/42 and the
other is at /proc/41/42; the parent dir inodes are different.  hmm.

> *However*, I would like to point out that we are holding ->i_sem on the
> procfs root at that point, so any blocking code in d_instantiate() would
> better be careful to avoid deadlocks if it wants to play with procfs itself -
> we are not in a locking-neutral situation here, spinlock or not.

"procfs root", or parent dir??