Messages in this thread | | | Subject | Re: New bug in patch and existing Linux code - race with install_page() (was: Re: [PATCH] 2.6.14 patch for supporting madvise(MADV_REMOVE)) | From | Badari Pulavarty <> | Date | Wed, 02 Nov 2005 14:02:33 -0800 |
| |
On Wed, 2005-11-02 at 21:55 +0000, Hugh Dickins wrote: > On Wed, 2 Nov 2005, Badari Pulavarty wrote: > > On Wed, 2005-11-02 at 20:54 +0100, Blaisorblade wrote: > > > > + /* XXX - Do we need both i_sem and i_allocsem all the way ? */ > > > > + down(&inode->i_sem); > > > > + down_write(&inode->i_alloc_sem); > > > > + unmap_mapping_range(mapping, offset, (end - offset), 1); > > > In my opinion, as already said, unmap_mapping_range can be called without > > > these two locks, as it operates only on mappings for the file. > > > > > > However currently it's called with these locks held in vmtruncate, but I think > > > the locks are held in that case only because we need to truncate the file, > > > and are hold in excess also across this call. > > > > I agree, I can push down the locking only for ->truncate_range - if > > no one has objections. (But again, it so special case - no one really > > cares about the performance of this interface ?). > > I can't remember why i_alloc_sem got introduced, and don't have time to > work it out: something to do with direct I/O races, perhaps? Someone > else must advise, perhaps you will be able to drop that one.
Yep. i_alloc_sem is supposed to protect DIO races with truncate.
> But I think you'd be very unwise to drop i_sem too. i_mmap_lock gets > dropped whenever preemption demands here, i_sem is what's preventing > someone else coming along and doing a concurrent truncate or remove. > You don't want that. > > Sorry, I've not yet had time to study your patch: I do intend to, > but cannot promise when. I fear it won't be as easy as making > these occasional responses.
Thanks Hugh. For now, I will leave those locks alone. We can re-visit later, if we really care about the performance of this interface. Better be safe than sorry.
Thanks, Badari
- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |