fs: Use rename lock and RCU for multi-step operations
The remaining usages for dcache_lock is to allow atomic, multi-step read-side
operations over the directory tree by excluding modifications to the tree.
Also, to walk in the leaf->root direction in the tree where we don't have
a natural d_lock ordering.
This could be accomplished by taking every d_lock, but this would mean a
huge number of locks and actually gets very tricky.
Solve this instead by using the rename seqlock for multi-step read-side
operations, retry in case of a rename so we don't walk up the wrong parent.
Concurrent dentry insertions are not serialised against. Concurrent deletes
are tricky when walking up the directory: our parent might have been deleted
when dropping locks so also need to check and retry for that.
We can also use the rename lock in cases where livelock is a worry (and it
is introduced in subsequent patch).
Signed-off-by: Nick Piggin <npiggin@kernel.dk>
diff --git a/include/linux/dcache.h b/include/linux/dcache.h
index bda5ec0..c963eba 100644
--- a/include/linux/dcache.h
+++ b/include/linux/dcache.h
@@ -180,6 +180,7 @@
#define DCACHE_FSNOTIFY_PARENT_WATCHED 0x0080 /* Parent inode is watched by some fsnotify listener */
#define DCACHE_CANT_MOUNT 0x0100
+#define DCACHE_GENOCIDE 0x0200
extern spinlock_t dcache_inode_lock;
extern spinlock_t dcache_lock;