From: Steve Dickson <SteveD@redhat.com>
Subject: Re: [RHEL5/FC6] [Patch 1/2] FS-Cache: error from cache: -105
Date: Sun, 10 Dec 2006 20:28:36 -0500
Bugzilla: 212831
Message-Id: <457CB444.3010303@RedHat.com>
Changelog: FS-Cache: dueling read/write processes fix




Steve Dickson wrote:
>The following patch series has patches to both NFS and
>FS-Cache the fix bz:
>
>https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=212831

David found a problem with this original patch that could
cause cache corruption when processes open the file for
both read and write simultaneously . The details are
in Comment #24 of the above bz.

Quick background. NFS only uses the FS-Cache on reads, and
when a file is open for write, the all caching is turned off until
the inode is recycled. This problem with this if a client
creates and populates a file, that data can not be cached (via
reads) until the inode is recycle which is an indefinite
amount of time .

So this patch fixes dueling read/write processes that David identified,
plus it enables FS-Caching after "last close". Meaning, the FS-Caching
is re-enabled after the file is any and all processes... Note closes
in the NFS world me all the data is flushed back...

steved.

--- linux-2.6.18.i686/fs/nfs/fscache.h.orig	2006-12-09 13:32:26.000000000 -0500
+++ linux-2.6.18.i686/fs/nfs/fscache.h	2006-12-09 17:54:49.000000000 -0500
@@ -49,11 +49,18 @@ static inline void nfs_fscache_unregiste
 	fscache_unregister_netfs(&nfs_cache_netfs);
 }
 /*
- * get the per-filehandle cookie for an NFS inode
+ * Initialize the fsc cookie and set the cache-able 
+ * bit if need be. 
  */
 static inline void nfs_fscache_init_cookie(struct inode *inode)
 {
+	struct super_block *sb = inode->i_sb;
+
 	NFS_I(inode)->fscache = NULL;
+	if (NFS_SB(sb)->flags & NFS_MOUNT_FSCACHE) {
+		if (S_ISREG(inode->i_mode))
+				set_bit(NFS_INO_FSCACHE, &NFS_FLAGS(inode));
+	}
 }
 
 /*
@@ -209,16 +216,35 @@ static inline void nfs_fscache_disable_c
 static inline void nfs_fscache_set_cookie(struct inode *inode, 
 	struct file *filp)
 {
-	if (!S_ISREG(inode->i_mode))
+	struct super_block *sb = inode->i_sb;
+
+	if (!(NFS_SB(sb)->flags & NFS_MOUNT_FSCACHE))
+		return;
+
+	if (!NFS_FSCACHE(inode))
 		return;
 
-	if ((filp->f_flags & O_ACCMODE) != O_RDONLY)
+	if ((filp->f_flags & O_ACCMODE) != O_RDONLY) {
 		nfs_fscache_disable_cookie(inode);
-	else
+		clear_bit(NFS_INO_FSCACHE, &NFS_FLAGS(inode));
+	} else
 		nfs_fscache_enable_cookie(inode);
 }
 
 /*
+ * On the last close, re-enable the cache if need be.
+ */
+static inline void nfs_fscache_reset_cookie(struct inode *inode)
+{
+	struct super_block *sb = inode->i_sb;
+
+	if (NFS_SB(sb)->flags & NFS_MOUNT_FSCACHE) {
+		if (list_empty(&NFS_I(inode)->open_files))
+			set_bit(NFS_INO_FSCACHE, &NFS_FLAGS(inode));
+	}
+}
+
+/*
  * install the VM ops for mmap() of an NFS file so that we can hold up writes
  * to pages on shared writable mappings until the store to the cache is
  * complete
@@ -452,6 +478,8 @@ static inline void nfs_fscache_release_c
 static inline void nfs_fscache_zap_cookie(struct inode *inode) {}
 static inline void nfs_fscache_renew_cookie(struct inode *inode) {}
 static inline void nfs_fscache_disable_cookie(struct inode *inode) {}
+static inline void nfs_fscache_set_cookie(struct inode *inode, struct file *filp) {}
+static inline void nfs_fscache_reset_cookie(struct inode *inode) {}
 static inline void nfs_fscache_install_vm_ops(struct inode *inode, struct vm_area_struct *vma) {}
 static inline void nfs_fscache_release_page(struct page *page) {}
 static inline void nfs_fscache_invalidate_page(struct page *page,
--- linux-2.6.18.i686/fs/nfs/inode.c.orig	2006-12-09 13:32:00.000000000 -0500
+++ linux-2.6.18.i686/fs/nfs/inode.c	2006-12-09 15:57:30.000000000 -0500
@@ -534,6 +534,7 @@ static void nfs_file_clear_open_context(
 		list_move_tail(&ctx->list, &NFS_I(inode)->open_files);
 		spin_unlock(&inode->i_lock);
 		put_nfs_open_context(ctx);
+		nfs_fscache_reset_cookie(inode);
 	}
 }
 
--- linux-2.6.18.i686/include/linux/nfs_fs.h.orig	2006-12-07 20:48:56.000000000 -0500
+++ linux-2.6.18.i686/include/linux/nfs_fs.h	2006-12-09 13:39:03.000000000 -0500
@@ -209,6 +209,7 @@ struct nfs_inode {
 #define NFS_INO_ADVISE_RDPLUS	(1)		/* advise readdirplus */
 #define NFS_INO_STALE		(2)		/* possible stale inode */
 #define NFS_INO_ACL_LRU_SET	(3)		/* Inode is on the LRU list */
+#define NFS_INO_FSCACHE	(4)		/* inode can be cached by FS-Cache */
 
 static inline struct nfs_inode *NFS_I(struct inode *inode)
 {
@@ -235,6 +236,7 @@ static inline struct nfs_inode *NFS_I(st
 
 #define NFS_FLAGS(inode)		(NFS_I(inode)->flags)
 #define NFS_STALE(inode)		(test_bit(NFS_INO_STALE, &NFS_FLAGS(inode)))
+#define NFS_FSCACHE(inode)		(test_bit(NFS_INO_FSCACHE, &NFS_FLAGS(inode)))
 
 #define NFS_FILEID(inode)		(NFS_I(inode)->fileid)