Re: [PATCH 17/17] NFS: nfs_migrate_page() does not wait for FS-Cache to finish with a page
From: Jonathan Nieder <hidden>
Date: 2012-07-21 16:57:41
Also in:
linux-fsdevel, lkml
Hi, In February, David Howells wrote:
nfs_migrate_page() does not wait for FS-Cache to finish with a page, probably leading to the following bad-page-state:
[...]
nfs_migrate_page() calls nfs_fscache_release_page() which doesn't actually wait - even if __GFP_WAIT is set. The reason that doesn't wait is that fscache_maybe_release_page() might deadlock the allocator as the work threads writing to the cache may all end up sleeping on memory allocation.
[...]
(1) Make nfs_migrate_page() wait. (2) Make fscache_maybe_release_page() honour the __GFP_WAIT flag. (3) Set a timeout around the wait. (4) Make nfs_migrate_page() return an error if the page is still busy. For the moment, I'll select (2) and (4).
[...]
quoted hunk
--- a/fs/nfs/write.c +++ b/fs/nfs/write.c@@ -1701,7 +1701,9 @@ int nfs_migrate_page(struct address_space *mapping, struct page *newpage, if (PagePrivate(page)) return -EBUSY; - nfs_fscache_release_page(page, GFP_KERNEL); + ret = -EBUSY; + if (!nfs_fscache_release_page(page, GFP_KERNEL)) + goto out; return migrate_page(mapping, newpage, page, mode); }
Small thing, but it looks like this was forward-ported incorrectly. Was this ever tested with CONFIG_MIGRATION enabled? Hope that helps, Jonathan