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closures: Fix race in closure_sync()

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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 <kent.overstreet@linux.dev>
This commit is contained in:
Kent Overstreet 2023-10-24 14:46:58 -04:00
parent 2bce6368c4
commit ee526b88ca
3 changed files with 13 additions and 1 deletions
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1
fs/bcachefs/fs-io-direct.c
View File

@ -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;

10
include/linux/closure.h
View File

@ -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);

3
lib/closure.c
View File

@ -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);