Patch "fscache: Clear outstanding writes when disabling a cookie" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

fscache: Clear outstanding writes when disabling a cookie

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
fscache-clear-outstanding-writes-when-disabling-a-cookie.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: David Howells <[email protected]>
Date: Tue, 23 May 2017 21:54:05 -0400
Subject: fscache: Clear outstanding writes when disabling a cookie

From: David Howells <[email protected]>

[ Upstream commit 6bdded59c8933940ac7e5b416448276ac89d1144 ]

fscache_disable_cookie() needs to clear the outstanding writes on the cookie it's disabling because they cannot be completed after.

Without this, fscache_nfs_open_file() gets stuck because it disables the cookie when the file is opened for writing but can't uncache the pages till afterwards - otherwise there's a race between the open routine and anyone who already has it open R/O and is still reading from it.

Looking in /proc/pid/stack of the offending process shows:

[<ffffffffa0142883>] __fscache_wait_on_page_write+0x82/0x9b [fscache]
[<ffffffffa014336e>] __fscache_uncache_all_inode_pages+0x91/0xe1 [fscache]
[<ffffffffa01740fa>] nfs_fscache_open_file+0x59/0x9e [nfs]
[<ffffffffa01ccf41>] nfs4_file_open+0x17f/0x1b8 [nfsv4]
[<ffffffff8117350e>] do_dentry_open+0x16d/0x2b7
[<ffffffff811743ac>] vfs_open+0x5c/0x65
[<ffffffff81184185>] path_openat+0x785/0x8fb
[<ffffffff81184343>] do_filp_open+0x48/0x9e
[<ffffffff81174710>] do_sys_open+0x13b/0x1cb
[<ffffffff811747b9>] SyS_open+0x19/0x1b
[<ffffffff81001c44>] do_syscall_64+0x80/0x17a
[<ffffffff8165c2da>] return_from_SYSCALL_64+0x0/0x7a

[<ffffffffffffffff>] 0xffffffffffffffff

---
 fs/fscache/cookie.c |    5 +++++
 fs/fscache/object.c |    6 ++++++
 2 files changed, 11 insertions(+)

@@ -542,6 +542,7 @@ void __fscache_disable_cookie(struct fsc
 		hlist_for_each_entry(object, &cookie->backing_objects, cookie_link) {
 			if (invalidate)
 				set_bit(FSCACHE_OBJECT_RETIRED, &object->flags);
+			clear_bit(FSCACHE_OBJECT_PENDING_WRITE, &object->flags);
 			fscache_raise_event(object, FSCACHE_OBJECT_EV_KILL);
 		}
 	} else {

@@ -560,6 +561,10 @@ void __fscache_disable_cookie(struct fsc
 		wait_on_atomic_t(&cookie->n_active, fscache_wait_atomic_t,
 				 TASK_UNINTERRUPTIBLE);
 
+	/* Make sure any pending writes are cancelled. */
+	if (cookie->def->type != FSCACHE_COOKIE_TYPE_INDEX)
+		fscache_invalidate_writes(cookie);
+
 	/* Reset the cookie state if it wasn't relinquished */
 	if (!test_bit(FSCACHE_COOKIE_RELINQUISHED, &cookie->flags)) {
 		atomic_inc(&cookie->n_active);

@@ -650,6 +650,12 @@ static const struct fscache_state *fscac
 	fscache_mark_object_dead(object);
 	object->oob_event_mask = 0;
 
+	if (test_bit(FSCACHE_OBJECT_RETIRED, &object->flags)) {
+		/* Reject any new read/write ops and abort any that are pending. */
+		clear_bit(FSCACHE_OBJECT_PENDING_WRITE, &object->flags);
+		fscache_cancel_all_ops(object);
+	}
+
 	if (list_empty(&object->dependents) &&
 	    object->n_ops == 0 &&
 	    object->n_children == 0)

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/fscache-clear-outstanding-writes-when-disabling-a-cookie.patch queue-4.4/fs-cache-initialise-stores_lock-in-netfs-cookie.patch queue-4.4/fscache-fix-dead-object-requeue.patch