On Mon, Sep 09, 2013 at 08:10:29PM +0100, Al Viro wrote:
> On Mon, Sep 09, 2013 at 02:46:57PM -0400, Waiman Long wrote:
>
> > I am fine with your proposed change as long as it gets the job done.
>
> I suspect that the real problem is the unlock part of read_seqretry_or_unlock();
> for d_walk() we want to be able to check if we need retry and continue walking
> if we do not. Let's do it that way: I've applied your patch as is, with the
> next step being
> * split read_seqretry_or_unlock():
> need_seqretry() (return (!(seq & 1) && read_seqretry(lock, seq))
> done_seqretry() (if (seq & 1) write_sequnlock(lock, seq)),
> your if (read_seqretry_or_unlock(&rename_lock, &seq))
> goto restart;
> becoming
> if (need_seqretry(&rename_lock, seq)) {
> seq = 1;
> goto restart;
> }
> done_seqretry(&rename_lock, seq);
>
> Then d_walk() is trivially massaged to use of read_seqbegin_or_lock(),
> need_seqretry() and done_seqretry(). Give me a few, I'll post it...
OK, how about this? It splits read_seqretry_or_unlock(), takes
rcu_read_{lock,unlock} in the callers and converts d_walk() to those
primitives. I've pushed that and your commit into vfs.git#experimental
(head at 48f5ec2, should propagate in a few); guys, please give it a look
and comment.
diff --git a/fs/dcache.c b/fs/dcache.c
index 38b1b09..b9caf47 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -100,30 +100,21 @@ static struct kmem_cache *dentry_cache __read_mostly;
*/
static inline void read_seqbegin_or_lock(seqlock_t *lock, int *seq)
{
- if (!(*seq & 1)) { /* Even */
+ if (!(*seq & 1)) /* Even */
*seq = read_seqbegin(lock);
- rcu_read_lock();
- } else /* Odd */
+ else /* Odd */
write_seqlock(lock);
}
-/**
- * read_seqretry_or_unlock - end a seqretry or lock block & return retry status
- * lock : sequence lock
- * seq : sequence number
- * Return: 1 to retry operation again, 0 to continue
- */
-static inline int read_seqretry_or_unlock(seqlock_t *lock, int *seq)
+static inline int need_seqretry(seqlock_t *lock, int seq)
{
- if (!(*seq & 1)) { /* Even */
- rcu_read_unlock();
- if (read_seqretry(lock, *seq)) {
- (*seq)++; /* Take writer lock */
- return 1;
- }
- } else /* Odd */
+ return !(seq & 1) && read_seqretry(lock, seq);
+}
+
+static inline void done_seqretry(seqlock_t *lock, int seq)
+{
+ if (seq & 1)
write_sequnlock(lock);
- return 0;
}
/*
@@ -1047,7 +1038,7 @@ void shrink_dcache_for_umount(struct super_block *sb)
* the parenthood after dropping the lock and check
* that the sequence number still matches.
*/
-static struct dentry *try_to_ascend(struct dentry *old, int locked, unsigned seq)
+static struct dentry *try_to_ascend(struct dentry *old, unsigned seq)
{
struct dentry *new = old->d_parent;
@@ -1061,7 +1052,7 @@ static struct dentry *try_to_ascend(struct dentry *old, int locked, unsigned seq
*/
if (new != old->d_parent ||
(old->d_flags & DCACHE_DENTRY_KILLED) ||
- (!locked && read_seqretry(&rename_lock, seq))) {
+ need_seqretry(&rename_lock, seq)) {
spin_unlock(&new->d_lock);
new = NULL;
}
@@ -1098,13 +1089,12 @@ static void d_walk(struct dentry *parent, void *data,
{
struct dentry *this_parent;
struct list_head *next;
- unsigned seq;
- int locked = 0;
+ unsigned seq = 0;
enum d_walk_ret ret;
bool retry = true;
- seq = read_seqbegin(&rename_lock);
again:
+ read_seqbegin_or_lock(&rename_lock, &seq);
this_parent = parent;
spin_lock(&this_parent->d_lock);
@@ -1158,13 +1148,13 @@ resume:
*/
if (this_parent != parent) {
struct dentry *child = this_parent;
- this_parent = try_to_ascend(this_parent, locked, seq);
+ this_parent = try_to_ascend(this_parent, seq);
if (!this_parent)
goto rename_retry;
next = child->d_u.d_child.next;
goto resume;
}
- if (!locked && read_seqretry(&rename_lock, seq)) {
+ if (need_seqretry(&rename_lock, seq)) {
spin_unlock(&this_parent->d_lock);
goto rename_retry;
}
@@ -1173,17 +1163,13 @@ resume:
out_unlock:
spin_unlock(&this_parent->d_lock);
- if (locked)
- write_sequnlock(&rename_lock);
+ done_seqretry(&rename_lock, seq);
return;
rename_retry:
if (!retry)
return;
- if (locked)
- goto again;
- locked = 1;
- write_seqlock(&rename_lock);
+ seq = 1;
goto again;
}
@@ -2745,6 +2731,7 @@ static int prepend_path(const struct path *path,
char *bptr;
int blen;
+ rcu_read_lock();
restart:
bptr = *buffer;
blen = *buflen;
@@ -2783,8 +2770,13 @@ restart:
dentry = parent;
}
- if (read_seqretry_or_unlock(&rename_lock, &seq))
+ if (!(seq & 1))
+ rcu_read_unlock();
+ if (need_seqretry(&rename_lock, seq)) {
+ seq = 1;
goto restart;
+ }
+ done_seqretry(&rename_lock, seq);
if (error >= 0 && bptr == *buffer) {
if (--blen < 0)
@@ -2957,6 +2949,7 @@ static char *__dentry_path(struct dentry *dentry, char *buf, int buflen)
int len, seq = 0;
int error = 0;
+ rcu_read_lock();
restart:
end = buf + buflen;
len = buflen;
@@ -2979,8 +2972,13 @@ restart:
retval = end;
dentry = parent;
}
- if (read_seqretry_or_unlock(&rename_lock, &seq))
+ if (!(seq & 1))
+ rcu_read_unlock();
+ if (need_seqretry(&rename_lock, seq)) {
+ seq = 1;
goto restart;
+ }
+ done_seqretry(&rename_lock, seq);
if (error)
goto Elong;
return retval;
--
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