On Wed, 1 Dec 2010 17:42:08 -0800 Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote: > On Wed, Dec 1, 2010 at 5:22 PM, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote: > > > > What we're talking about is races against memory reclaim, unmount, etc. > > Ahh. Those I can believe in. Although I think they'd almost > incidentally be fixed by making inode freeing (which is where the > 'struct address_space' is embedded) RCU-safe, which we're going to do > anyway in 38. Then we could make the vmscan code just be a rcu-read > section. I didn't know that aspect of it. It will be nice to plug this race - it's been there for so long because nobody was able to think of an acceptable way of fixing it by direct means (synchronous locking, refcounting, etc). Taking a ref on the inode doesn't work, because we can't run iput_final() in direct-reclaim contexts (lock ordering snafus). vmscan is the problematic path - I _think_ all other code paths which remove pagecache have an inode ref. But this assumes that inode->i_mapping points at inode->i_data! Need to think about the situation where it points at a different inode's i_data - in that case these callers may have a ref on the wrong inode. > Of course, I do think the race is basically impossible to hit in > practice regardless. Actually I was able to hit the race back in late 2.5 or thereabouts. Really massive memory pressure caused vmscan->icache_shrinker to free the inode/address_space while another CPU in vmscan was playing with the address_space. That was quite a debugging session ;) -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
