[PATCH] NFS: Fix race in nfs_release_page()

    NFS: Fix race in nfs_release_page()

    invalidate_inode_pages2() may find the dirty bit has been set on a page
    owing to the fact that the page may still be mapped after it was locked.
    Only after the call to unmap_mapping_range() are we sure that the page
    can no longer be dirtied.
    In order to fix this, NFS has hooked the releasepage() method and tries
    to write the page out between the call to unmap_mapping_range() and the
    call to remove_mapping(). This, however leads to deadlocks in the page
    reclaim code, where the page may be locked without holding a reference
    to the inode or dentry.

    Fix is to add a new address_space_operation, launder_page(), which will
    attempt to write out a dirty page without releasing the page lock.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

    Also, the bare SetPageDirty() can skew all sort of accounting leading to
    other nasties.

[akpm@osdl.org: cleanup]
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Trond Myklebust <Trond.Myklebust@netapp.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 8 insertions, 8 deletions

diff --git a/fs/nfs/file.c b/fs/nfs/file.c
index 0dd6be346aa7..fab20d06d936 100644
--- a/fs/nfs/file.c
+++ b/fs/nfs/file.c
@@ -315,14 +315,13 @@ static void nfs_invalidate_page(struct page *page, unsigned long offset)
 
 static int nfs_release_page(struct page *page, gfp_t gfp)
 {
-	/*
-	 * Avoid deadlock on nfs_wait_on_request().
-	 */
-	if (!(gfp & __GFP_FS))
-		return 0;
-	/* Hack... Force nfs_wb_page() to write out the page */
-	SetPageDirty(page);
-	return !nfs_wb_page(page->mapping->host, page);
+	/* If PagePrivate() is set, then the page is not freeable */
+	return 0;
+}
+
+static int nfs_launder_page(struct page *page)
+{
+	return nfs_wb_page(page->mapping->host, page);
 }
 
 const struct address_space_operations nfs_file_aops = {
@@ -338,6 +337,7 @@ const struct address_space_operations nfs_file_aops = {
 #ifdef CONFIG_NFS_DIRECTIO
 	.direct_IO = nfs_direct_IO,
 #endif
+	.launder_page = nfs_launder_page,
 };
 
 static ssize_t nfs_file_write(struct kiocb *iocb, const struct iovec *iov,