Re: [PATCH] Fix races in 2.4.2-ac22 SysV shared memory

Alexander Viro (viro@math.psu.edu)
Fri, 23 Mar 2001 17:23:29 -0500 (EST)


On Fri, 23 Mar 2001, Alan Cox wrote:

> > On Fri, 23 Mar 2001, Stephen C. Tweedie wrote:
> > >
> > > The patch below is for two races in sysV shared memory.
> >
> > + spin_lock (&info->lock);
> > +
> > + /* The shmem_swp_entry() call may have blocked, and
> > + * shmem_writepage may have been moving a page between the page
> > + * cache and swap cache. We need to recheck the page cache
> > + * under the protection of the info->lock spinlock. */
> > +
> > + page = find_lock_page(mapping, idx);
> >
> > Ehh.. Sleeping with the spin-lock held? Sounds like a truly bad idea.
>
> Umm find_lock_page doesnt sleep does it ?

It certainly does. find_lock_page() -> __find_lock_page() -> lock_page() ->
-> __lock_page() -> schedule().

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