From 949854d02455080d20cd3e1db28a3a18daf7599d Mon Sep 17 00:00:00 2001 From: Nick Piggin Date: Fri, 7 Jan 2011 17:49:37 +1100 Subject: 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 --- fs/nfs/namespace.c | 14 +++++++++++++- 1 file changed, 13 insertions(+), 1 deletion(-) (limited to 'fs/nfs') diff --git a/fs/nfs/namespace.c b/fs/nfs/namespace.c index db6aa3673cf..78c0ebb0b07 100644 --- a/fs/nfs/namespace.c +++ b/fs/nfs/namespace.c @@ -49,11 +49,17 @@ char *nfs_path(const char *base, const struct dentry *dentry, char *buffer, ssize_t buflen) { - char *end = buffer+buflen; + char *end; int namelen; + unsigned seq; +rename_retry: + end = buffer+buflen; *--end = '\0'; buflen--; + + seq = read_seqbegin(&rename_lock); + rcu_read_lock(); spin_lock(&dcache_lock); while (!IS_ROOT(dentry) && dentry != droot) { namelen = dentry->d_name.len; @@ -66,6 +72,9 @@ char *nfs_path(const char *base, dentry = dentry->d_parent; } spin_unlock(&dcache_lock); + rcu_read_unlock(); + if (read_seqretry(&rename_lock, seq)) + goto rename_retry; if (*end != '/') { if (--buflen < 0) goto Elong; @@ -83,6 +92,9 @@ char *nfs_path(const char *base, return end; Elong_unlock: spin_unlock(&dcache_lock); + rcu_read_unlock(); + if (read_seqretry(&rename_lock, seq)) + goto rename_retry; Elong: return ERR_PTR(-ENAMETOOLONG); } -- cgit v1.2.3-18-g5258