bcachefs: fix seqmutex_relock()

We were grabbing the sequence number before unlock incremented it - fix
this by moving the increment to seqmutex_lock() (so the seqmutex_relock()
failure path skips the mutex_trylock()), and returning the sequence
number from unlock(), to make the API simpler and safer.

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

diff --git a/fs/bcachefs/debug.c b/fs/bcachefs/debug.c
index 51cbf39283612c53f8ea3412af97acd6ded3cd7a..8ec2d44e4956edede156923b4e0aaebdbcf3ffc3 100644 (file)
--- a/fs/bcachefs/debug.c
+++ b/fs/bcachefs/debug.c
@@ -575,7 +575,6 @@ static ssize_t bch2_btree_transactions_read(struct file *file, char __user *buf,
        struct bch_fs *c = i->c;
        struct btree_trans *trans;
        ssize_t ret = 0;
-       u32 seq;
 
        i->ubuf = buf;
        i->size = size;
@@ -589,8 +588,7 @@ restart:
                        continue;
 
                closure_get(&trans->ref);
-               seq = seqmutex_seq(&c->btree_trans_lock);
-               seqmutex_unlock(&c->btree_trans_lock);
+               u32 seq = seqmutex_unlock(&c->btree_trans_lock);
 
                ret = flush_buf(i);
                if (ret) {
@@ -811,7 +809,6 @@ static ssize_t bch2_btree_deadlock_read(struct file *file, char __user *buf,
        struct bch_fs *c = i->c;
        struct btree_trans *trans;
        ssize_t ret = 0;
-       u32 seq;
 
        i->ubuf = buf;
        i->size = size;
@@ -828,8 +825,7 @@ restart:
                        continue;
 
                closure_get(&trans->ref);
-               seq = seqmutex_seq(&c->btree_trans_lock);
-               seqmutex_unlock(&c->btree_trans_lock);
+               u32 seq = seqmutex_unlock(&c->btree_trans_lock);
 
                ret = flush_buf(i);
                if (ret) {

diff --git a/fs/bcachefs/seqmutex.h b/fs/bcachefs/seqmutex.h
index c1860d8163fb140a1a6f3bbd5679c455480ddb50..c4b3d8d3f4149cdb41c217404598e83f69cfafc5 100644 (file)
--- a/fs/bcachefs/seqmutex.h
+++ b/fs/bcachefs/seqmutex.h
@@ -19,17 +19,14 @@ static inline bool seqmutex_trylock(struct seqmutex *lock)
 static inline void seqmutex_lock(struct seqmutex *lock)
 {
        mutex_lock(&lock->lock);
-}
-
-static inline void seqmutex_unlock(struct seqmutex *lock)
-{
        lock->seq++;
-       mutex_unlock(&lock->lock);
 }
 
-static inline u32 seqmutex_seq(struct seqmutex *lock)
+static inline u32 seqmutex_unlock(struct seqmutex *lock)
 {
-       return lock->seq;
+       u32 seq = lock->seq;
+       mutex_unlock(&lock->lock);
+       return seq;
 }
 
 static inline bool seqmutex_relock(struct seqmutex *lock, u32 seq)