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authorNick Piggin <npiggin@kernel.dk>2011-01-07 17:49:37 +1100
committerNick Piggin <npiggin@kernel.dk>2011-01-07 17:50:22 +1100
commit949854d02455080d20cd3e1db28a3a18daf7599d (patch)
tree9b13a6f86c1d0b91e462a471e53b0e717036b18e /fs/nfs/namespace.c
parent9abca36087288fe28de4749c71ca003d4b9e3ed0 (diff)
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>
Diffstat (limited to 'fs/nfs/namespace.c')
-rw-r--r--fs/nfs/namespace.c14
1 files changed, 13 insertions, 1 deletions
diff --git a/fs/nfs/namespace.c b/fs/nfs/namespace.c
index db6aa3673cf3..78c0ebb0b07c 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);
}