split read_seqretry_or_unlock(), convert d_walk() to resulting primitives

Separate "check if we need to retry" from "unlock if we are done and
had seq_writelock"; that allows to use these guys in d_walk(), where
we need to recheck every time we ascend back to parent, but do *not*
want to unlock until the very end.  Lift rcu_read_lock/rcu_read_unlock
out into callers.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --git a/fs/dcache.c b/fs/dcache.c
index 38b1b09..b9caf47 100644 (file)
--- 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;