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author | Nick Piggin <npiggin@kernel.dk> | 2011-01-07 06:49:37 (GMT) |
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committer | Nick Piggin <npiggin@kernel.dk> | 2011-01-07 06:50:22 (GMT) |
commit | 949854d02455080d20cd3e1db28a3a18daf7599d (patch) | |
tree | 9b13a6f86c1d0b91e462a471e53b0e717036b18e /fs/autofs4 | |
parent | 9abca36087288fe28de4749c71ca003d4b9e3ed0 (diff) | |
download | linux-fsl-qoriq-949854d02455080d20cd3e1db28a3a18daf7599d.tar.xz |
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')
-rw-r--r-- | fs/autofs4/waitq.c | 18 |
1 files changed, 15 insertions, 3 deletions
diff --git a/fs/autofs4/waitq.c b/fs/autofs4/waitq.c index 2341375..4be8f77 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; } |