From 2bce6368c46b835a133f7f4946eea9c4513828dd Mon Sep 17 00:00:00 2001 From: Kent Overstreet Date: Tue, 24 Oct 2023 14:46:58 -0400 Subject: closures: Better memory barriers atomic_(dec|sub)_return_release() are a thing now - use them. Also, delete the useless barrier in set_closure_fn(): it's redundant with the memory barrier in closure_put(0. Since closure_put() would now otherwise just have a release barrier, we also need a new barrier when the ref hits 0 - smp_acquire__after_ctrl_dep(). Signed-off-by: Kent Overstreet --- lib/closure.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) (limited to 'lib') diff --git a/lib/closure.c b/lib/closure.c index 0855e698ced1..501dfa277b59 100644 --- a/lib/closure.c +++ b/lib/closure.c @@ -21,6 +21,8 @@ static inline void closure_put_after_sub(struct closure *cl, int flags) BUG_ON(!r && (flags & ~CLOSURE_DESTRUCTOR)); if (!r) { + smp_acquire__after_ctrl_dep(); + if (cl->fn && !(flags & CLOSURE_DESTRUCTOR)) { atomic_set(&cl->remaining, CLOSURE_REMAINING_INITIALIZER); @@ -43,7 +45,7 @@ static inline void closure_put_after_sub(struct closure *cl, int flags) /* For clearing flags with the same atomic op as a put */ void closure_sub(struct closure *cl, int v) { - closure_put_after_sub(cl, atomic_sub_return(v, &cl->remaining)); + closure_put_after_sub(cl, atomic_sub_return_release(v, &cl->remaining)); } EXPORT_SYMBOL(closure_sub); @@ -52,7 +54,7 @@ EXPORT_SYMBOL(closure_sub); */ void closure_put(struct closure *cl) { - closure_put_after_sub(cl, atomic_dec_return(&cl->remaining)); + closure_put_after_sub(cl, atomic_dec_return_release(&cl->remaining)); } EXPORT_SYMBOL(closure_put); -- cgit v1.2.3 From ee526b88caaa4b4182144bf2576af2c3b1e9c759 Mon Sep 17 00:00:00 2001 From: Kent Overstreet Date: Tue, 24 Oct 2023 14:46:58 -0400 Subject: closures: Fix race in closure_sync() 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 --- fs/bcachefs/fs-io-direct.c | 1 + include/linux/closure.h | 10 +++++++++- lib/closure.c | 3 +++ 3 files changed, 13 insertions(+), 1 deletion(-) (limited to 'lib') 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); -- cgit v1.2.3