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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/autofs4/waitq.c
parent9abca36087288fe28de4749c71ca003d4b9e3ed0 (diff)
downloadvexpress-lsk-949854d02455080d20cd3e1db28a3a18daf7599d.tar.gz
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/autofs4/waitq.c')
-rw-r--r--fs/autofs4/waitq.c18
1 files changed, 15 insertions, 3 deletions
diff --git a/fs/autofs4/waitq.c b/fs/autofs4/waitq.c
index 2341375386f..4be8f778a41 100644
--- a/fs/autofs4/waitq.c
+++ b/fs/autofs4/waitq.c
@@ -186,16 +186,25 @@ static int autofs4_getpath(struct autofs_sb_info *sbi,
{
struct dentry *root = sbi->sb->s_root;
struct dentry *tmp;
- char *buf = *name;
+ char *buf;
char *p;
- int len = 0;
-
+ int len;
+ unsigned seq;
+
+rename_retry:
+ buf = *name;
+ len = 0;
+ seq = read_seqbegin(&rename_lock);
+ rcu_read_lock();
spin_lock(&dcache_lock);
for (tmp = dentry ; tmp != root ; tmp = tmp->d_parent)
len += tmp->d_name.len + 1;
if (!len || --len > NAME_MAX) {
spin_unlock(&dcache_lock);
+ rcu_read_unlock();
+ if (read_seqretry(&rename_lock, seq))
+ goto rename_retry;
return 0;
}
@@ -209,6 +218,9 @@ static int autofs4_getpath(struct autofs_sb_info *sbi,
strncpy(p, tmp->d_name.name, tmp->d_name.len);
}
spin_unlock(&dcache_lock);
+ rcu_read_unlock();
+ if (read_seqretry(&rename_lock, seq))
+ goto rename_retry;
return len;
}