From 06efa5f30c28eaf237247ca8c4cb46eb62cb6bd9 Mon Sep 17 00:00:00 2001
From: Kent Overstreet <kent.overstreet@linux.dev>
Date: Sat, 22 Jun 2024 21:38:58 -0400
Subject: [PATCH] closures: closure_get_not_zero(), closure_return_sync()
Provide new primitives for solving a lifetime issue with bcachefs
btree_trans objects.
closure_sync_return(): like closure_sync(), wait synchronously for any
outstanding gets. like closure_return, the closure is considered
"finished" and the ref left at 0.
closure_get_not_zero(): get a ref on a closure if it's alive, i.e. the
ref is not zero.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
---
include/linux/closure.h | 23 ++++++++++++++++++
lib/closure.c | 52 ++++++++++++++++++++++++++++++++++++-----
2 files changed, 69 insertions(+), 6 deletions(-)
diff --git a/include/linux/closure.h b/include/linux/closure.h
index 99155df162d03..59b8c06b11ff3 100644
--- a/include/linux/closure.h
+++ b/include/linux/closure.h
@@ -284,6 +284,21 @@ static inline void closure_get(struct closure *cl)
#endif
}
+/**
+ * closure_get_not_zero
+ */
+static inline bool closure_get_not_zero(struct closure *cl)
+{
+ unsigned old = atomic_read(&cl->remaining);
+ do {
+ if (!(old & CLOSURE_REMAINING_MASK))
+ return false;
+
+ } while (!atomic_try_cmpxchg_acquire(&cl->remaining, &old, old + 1));
+
+ return true;
+}
+
/**
* closure_init - Initialize a closure, setting the refcount to 1
* @cl: closure to initialize
@@ -310,6 +325,12 @@ static inline void closure_init_stack(struct closure *cl)
atomic_set(&cl->remaining, CLOSURE_REMAINING_INITIALIZER);
}
+static inline void closure_init_stack_release(struct closure *cl)
+{
+ memset(cl, 0, sizeof(struct closure));
+ atomic_set_release(&cl->remaining, CLOSURE_REMAINING_INITIALIZER);
+}
+
/**
* closure_wake_up - wake up all closures on a wait list,
* with memory barrier
@@ -355,6 +376,8 @@ do { \
*/
#define closure_return(_cl) continue_at((_cl), NULL, NULL)
+void closure_return_sync(struct closure *cl);
+
/**
* continue_at_nobarrier - jump to another function without barrier
*
diff --git a/lib/closure.c b/lib/closure.c
index 2e1ee9fdec081..c971216d9d774 100644
--- a/lib/closure.c
+++ b/lib/closure.c
@@ -13,7 +13,7 @@
#include <linux/seq_file.h>
#include <linux/sched/debug.h>
-static inline void closure_put_after_sub(struct closure *cl, int flags)
+static inline void closure_put_after_sub_checks(int flags)
{
int r = flags & CLOSURE_REMAINING_MASK;
@@ -22,12 +22,17 @@ static inline void closure_put_after_sub(struct closure *cl, int flags)
flags & CLOSURE_GUARD_MASK, (unsigned) __fls(r)))
r &= ~CLOSURE_GUARD_MASK;
- if (!r) {
- smp_acquire__after_ctrl_dep();
+ WARN(!r && (flags & ~CLOSURE_DESTRUCTOR),
+ "closure ref hit 0 with incorrect flags set: %x (%u)",
+ flags & ~CLOSURE_DESTRUCTOR, (unsigned) __fls(flags));
+}
+
+static inline void closure_put_after_sub(struct closure *cl, int flags)
+{
+ closure_put_after_sub_checks(flags);
- WARN(flags & ~CLOSURE_DESTRUCTOR,
- "closure ref hit 0 with incorrect flags set: %x (%u)",
- flags & ~CLOSURE_DESTRUCTOR, (unsigned) __fls(flags));
+ if (!(flags & CLOSURE_REMAINING_MASK)) {
+ smp_acquire__after_ctrl_dep();
cl->closure_get_happened = false;
@@ -145,6 +150,41 @@ void __sched __closure_sync(struct closure *cl)
}
EXPORT_SYMBOL(__closure_sync);
+/*
+ * closure_return_sync - finish running a closure, synchronously (i.e. waiting
+ * for outstanding get()s to finish) and returning once closure refcount is 0.
+ *
+ * Unlike closure_sync() this doesn't reinit the ref to 1; subsequent
+ * closure_get_not_zero() calls waill fail.
+ */
+void __sched closure_return_sync(struct closure *cl)
+{
+ struct closure_syncer s = { .task = current };
+
+ cl->s = &s;
+ set_closure_fn(cl, closure_sync_fn, NULL);
+
+ unsigned flags = atomic_sub_return_release(1 + CLOSURE_RUNNING - CLOSURE_DESTRUCTOR,
+ &cl->remaining);
+
+ closure_put_after_sub_checks(flags);
+
+ if (unlikely(flags & CLOSURE_REMAINING_MASK)) {
+ while (1) {
+ set_current_state(TASK_UNINTERRUPTIBLE);
+ if (s.done)
+ break;
+ schedule();
+ }
+
+ __set_current_state(TASK_RUNNING);
+ }
+
+ if (cl->parent)
+ closure_put(cl->parent);
+}
+EXPORT_SYMBOL(closure_return_sync);
+
int __sched __closure_sync_timeout(struct closure *cl, unsigned long timeout)
{
struct closure_syncer s = { .task = current };
--
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