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fs: dcache reduce d_parent locking

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Use RCU to simplify locking in dget_parent.

Signed-off-by: Nick Piggin <npiggin@kernel.dk>
This commit is contained in:
Nick Piggin 2011-01-07 17:49:44 +11:00
parent dc0474be3e
commit a734eb458a
1 changed files with 12 additions and 9 deletions
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21
fs/dcache.c
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@ -446,24 +446,27 @@ struct dentry *dget_parent(struct dentry *dentry)
struct dentry *ret; struct dentry *ret;
repeat: repeat:
spin_lock(&dentry->d_lock); /*
* Don't need rcu_dereference because we re-check it was correct under
* the lock.
*/
rcu_read_lock();
ret = dentry->d_parent; ret = dentry->d_parent;
if (!ret) if (!ret) {
goto out; rcu_read_unlock();
if (dentry == ret) {
ret->d_count++;
goto out; goto out;
} }
if (!spin_trylock(&ret->d_lock)) { spin_lock(&ret->d_lock);
spin_unlock(&dentry->d_lock); if (unlikely(ret != dentry->d_parent)) {
cpu_relax(); spin_unlock(&ret->d_lock);
rcu_read_unlock();
goto repeat; goto repeat;
} }
rcu_read_unlock();
BUG_ON(!ret->d_count); BUG_ON(!ret->d_count);
ret->d_count++; ret->d_count++;
spin_unlock(&ret->d_lock); spin_unlock(&ret->d_lock);
out: out:
spin_unlock(&dentry->d_lock);
return ret; return ret;
} }
EXPORT_SYMBOL(dget_parent); EXPORT_SYMBOL(dget_parent);