Hi, On Mon, 16 Oct 2023 22:23:14 +0900 Masami Hiramatsu (Google) <mhira...@kernel.org> wrote:
> Hi Peter, > > This freelist has been introduced by you, is it OK to remove this because no > other user exists? I'll pick this on my probes/for-next branch. If there is any issue reported, I'll revert it. Thank you, > > Thank you, > > On Sun, 15 Oct 2023 13:32:50 +0800 > "wuqiang.matt" <wuqiang.m...@bytedance.com> wrote: > > > This patch will remove freelist.h from kernel source tree, since the > > only use cases (kretprobe and rethook) are converted to objpool. > > > > Signed-off-by: wuqiang.matt <wuqiang.m...@bytedance.com> > > --- > > include/linux/freelist.h | 129 --------------------------------------- > > 1 file changed, 129 deletions(-) > > delete mode 100644 include/linux/freelist.h > > > > diff --git a/include/linux/freelist.h b/include/linux/freelist.h > > deleted file mode 100644 > > index fc1842b96469..000000000000 > > --- a/include/linux/freelist.h > > +++ /dev/null > > @@ -1,129 +0,0 @@ > > -/* SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause */ > > -#ifndef FREELIST_H > > -#define FREELIST_H > > - > > -#include <linux/atomic.h> > > - > > -/* > > - * Copyright: came...@moodycamel.com > > - * > > - * A simple CAS-based lock-free free list. Not the fastest thing in the > > world > > - * under heavy contention, but simple and correct (assuming nodes are never > > - * freed until after the free list is destroyed), and fairly speedy under > > low > > - * contention. > > - * > > - * Adapted from: > > https://moodycamel.com/blog/2014/solving-the-aba-problem-for-lock-free-free-lists > > - */ > > - > > -struct freelist_node { > > - atomic_t refs; > > - struct freelist_node *next; > > -}; > > - > > -struct freelist_head { > > - struct freelist_node *head; > > -}; > > - > > -#define REFS_ON_FREELIST 0x80000000 > > -#define REFS_MASK 0x7FFFFFFF > > - > > -static inline void __freelist_add(struct freelist_node *node, struct > > freelist_head *list) > > -{ > > - /* > > - * Since the refcount is zero, and nobody can increase it once it's > > - * zero (except us, and we run only one copy of this method per node at > > - * a time, i.e. the single thread case), then we know we can safely > > - * change the next pointer of the node; however, once the refcount is > > - * back above zero, then other threads could increase it (happens under > > - * heavy contention, when the refcount goes to zero in between a load > > - * and a refcount increment of a node in try_get, then back up to > > - * something non-zero, then the refcount increment is done by the other > > - * thread) -- so if the CAS to add the node to the actual list fails, > > - * decrese the refcount and leave the add operation to the next thread > > - * who puts the refcount back to zero (which could be us, hence the > > - * loop). > > - */ > > - struct freelist_node *head = READ_ONCE(list->head); > > - > > - for (;;) { > > - WRITE_ONCE(node->next, head); > > - atomic_set_release(&node->refs, 1); > > - > > - if (!try_cmpxchg_release(&list->head, &head, node)) { > > - /* > > - * Hmm, the add failed, but we can only try again when > > - * the refcount goes back to zero. > > - */ > > - if (atomic_fetch_add_release(REFS_ON_FREELIST - 1, > > &node->refs) == 1) > > - continue; > > - } > > - return; > > - } > > -} > > - > > -static inline void freelist_add(struct freelist_node *node, struct > > freelist_head *list) > > -{ > > - /* > > - * We know that the should-be-on-freelist bit is 0 at this point, so > > - * it's safe to set it using a fetch_add. > > - */ > > - if (!atomic_fetch_add_release(REFS_ON_FREELIST, &node->refs)) { > > - /* > > - * Oh look! We were the last ones referencing this node, and we > > - * know we want to add it to the free list, so let's do it! > > - */ > > - __freelist_add(node, list); > > - } > > -} > > - > > -static inline struct freelist_node *freelist_try_get(struct freelist_head > > *list) > > -{ > > - struct freelist_node *prev, *next, *head = > > smp_load_acquire(&list->head); > > - unsigned int refs; > > - > > - while (head) { > > - prev = head; > > - refs = atomic_read(&head->refs); > > - if ((refs & REFS_MASK) == 0 || > > - !atomic_try_cmpxchg_acquire(&head->refs, &refs, refs+1)) { > > - head = smp_load_acquire(&list->head); > > - continue; > > - } > > - > > - /* > > - * Good, reference count has been incremented (it wasn't at > > - * zero), which means we can read the next and not worry about > > - * it changing between now and the time we do the CAS. > > - */ > > - next = READ_ONCE(head->next); > > - if (try_cmpxchg_acquire(&list->head, &head, next)) { > > - /* > > - * Yay, got the node. This means it was on the list, > > - * which means should-be-on-freelist must be false no > > - * matter the refcount (because nobody else knows it's > > - * been taken off yet, it can't have been put back on). > > - */ > > - WARN_ON_ONCE(atomic_read(&head->refs) & > > REFS_ON_FREELIST); > > - > > - /* > > - * Decrease refcount twice, once for our ref, and once > > - * for the list's ref. > > - */ > > - atomic_fetch_add(-2, &head->refs); > > - > > - return head; > > - } > > - > > - /* > > - * OK, the head must have changed on us, but we still need to > > decrement > > - * the refcount we increased. > > - */ > > - refs = atomic_fetch_add(-1, &prev->refs); > > - if (refs == REFS_ON_FREELIST + 1) > > - __freelist_add(prev, list); > > - } > > - > > - return NULL; > > -} > > - > > -#endif /* FREELIST_H */ > > -- > > 2.40.1 > > > > > -- > Masami Hiramatsu (Google) <mhira...@kernel.org> -- Masami Hiramatsu (Google) <mhira...@kernel.org>
