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

[Alexander Viro <viro@math.psu.edu>]

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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