As pointed out by Linus, closure_sync() was racy; we could skip blocking immediately after a get() and a put(), but then that would skip any barrier corresponding to the other thread's put() barrier.
To fix this, always do the full __closure_sync() sequence whenever any get() has happened and the closure might have been used by other threads. Signed-off-by: Kent Overstreet <[email protected]> --- fs/bcachefs/fs-io-direct.c | 1 + include/linux/closure.h | 10 +++++++++- lib/closure.c | 3 +++ 3 files changed, 13 insertions(+), 1 deletion(-) diff --git a/fs/bcachefs/fs-io-direct.c b/fs/bcachefs/fs-io-direct.c index 6a9557e7ecab..5b42a76c4796 100644 --- a/fs/bcachefs/fs-io-direct.c +++ b/fs/bcachefs/fs-io-direct.c @@ -113,6 +113,7 @@ static int bch2_direct_IO_read(struct kiocb *req, struct iov_iter *iter) } else { atomic_set(&dio->cl.remaining, CLOSURE_REMAINING_INITIALIZER + 1); + dio->cl.closure_get_happened = true; } dio->req = req; diff --git a/include/linux/closure.h b/include/linux/closure.h index bdab17050bc8..de7bb47d8a46 100644 --- a/include/linux/closure.h +++ b/include/linux/closure.h @@ -154,6 +154,7 @@ struct closure { struct closure *parent; atomic_t remaining; + bool closure_get_happened; #ifdef CONFIG_DEBUG_CLOSURES #define CLOSURE_MAGIC_DEAD 0xc054dead @@ -185,7 +186,11 @@ static inline unsigned closure_nr_remaining(struct closure *cl) */ static inline void closure_sync(struct closure *cl) { - if (closure_nr_remaining(cl) != 1) +#ifdef CONFIG_DEBUG_CLOSURES + BUG_ON(closure_nr_remaining(cl) != 1 && !cl->closure_get_happened); +#endif + + if (cl->closure_get_happened) __closure_sync(cl); } @@ -257,6 +262,8 @@ static inline void closure_queue(struct closure *cl) */ static inline void closure_get(struct closure *cl) { + cl->closure_get_happened = true; + #ifdef CONFIG_DEBUG_CLOSURES BUG_ON((atomic_inc_return(&cl->remaining) & CLOSURE_REMAINING_MASK) <= 1); @@ -279,6 +286,7 @@ static inline void closure_init(struct closure *cl, struct closure *parent) closure_get(parent); atomic_set(&cl->remaining, CLOSURE_REMAINING_INITIALIZER); + cl->closure_get_happened = false; closure_debug_create(cl); closure_set_ip(cl); diff --git a/lib/closure.c b/lib/closure.c index 501dfa277b59..f86c9eeafb35 100644 --- a/lib/closure.c +++ b/lib/closure.c @@ -23,6 +23,8 @@ static inline void closure_put_after_sub(struct closure *cl, int flags) if (!r) { smp_acquire__after_ctrl_dep(); + cl->closure_get_happened = false; + if (cl->fn && !(flags & CLOSURE_DESTRUCTOR)) { atomic_set(&cl->remaining, CLOSURE_REMAINING_INITIALIZER); @@ -92,6 +94,7 @@ bool closure_wait(struct closure_waitlist *waitlist, struct closure *cl) if (atomic_read(&cl->remaining) & CLOSURE_WAITING) return false; + cl->closure_get_happened = true; closure_set_waiting(cl, _RET_IP_); atomic_add(CLOSURE_WAITING + 1, &cl->remaining); llist_add(&cl->list, &waitlist->list); -- 2.42.0
