From 5f56f409b5142bb4e88e1f64dedeb4a76c678177 Mon Sep 17 00:00:00 2001 From: Wei Wang Date: Sat, 17 Jun 2017 10:42:27 -0700 Subject: [PATCH] net: introduce DST_NOGC in dst_release() to destroy dst based on refcnt The current mechanism of freeing dst is a bit complicated. dst has its ref count and when user grabs the reference to the dst, the ref count is properly taken in most cases except in IPv4/IPv6/decnet/xfrm routing code due to some historic reasons. If the reference to dst is always taken properly, we should be able to simplify the logic in dst_release() to destroy dst when dst->__refcnt drops from 1 to 0. And this should be the only condition to determine if we can call dst_destroy(). And as dst is always ref counted, there is no need for a dst garbage list to hold the dst entries that already get removed by the routing code but are still held by other users. And the task to periodically check the list to free dst if ref count become 0 is also not needed anymore. This patch introduces a temporary flag DST_NOGC(no garbage collector). If it is set in the dst, dst_release() will call dst_destroy() when dst->__refcnt drops to 0. dst_hold_safe() will also check for this flag and do atomic_inc_not_zero() similar as DST_NOCACHE to avoid double free issue. This temporary flag is mainly used so that we can make the transition component by component without breaking other parts. This flag will be removed after all components are properly transitioned. This patch also introduces a new function dst_release_immediate() which destroys dst without waiting on the rcu when refcnt drops to 0. It will be used in later patches. Follow-up patches will correct all the places to properly take ref count on dst and mark DST_NOGC. dst_release() or dst_release_immediate() will be used to release the dst instead of dst_free() and its related functions. And final clean-up patch will remove the DST_NOGC flag. Signed-off-by: Wei Wang Acked-by: Martin KaFai Lau Signed-off-by: David S. Miller --- include/net/dst.h | 5 ++++- net/core/dst.c | 20 ++++++++++++++++++-- 2 files changed, 22 insertions(+), 3 deletions(-) diff --git a/include/net/dst.h b/include/net/dst.h index 1969008783d8..2735d5a1e774 100644 --- a/include/net/dst.h +++ b/include/net/dst.h @@ -58,6 +58,7 @@ struct dst_entry { #define DST_XFRM_TUNNEL 0x0080 #define DST_XFRM_QUEUE 0x0100 #define DST_METADATA 0x0200 +#define DST_NOGC 0x0400 short error; @@ -278,6 +279,8 @@ static inline struct dst_entry *dst_clone(struct dst_entry *dst) void dst_release(struct dst_entry *dst); +void dst_release_immediate(struct dst_entry *dst); + static inline void refdst_drop(unsigned long refdst) { if (!(refdst & SKB_DST_NOREF)) @@ -334,7 +337,7 @@ static inline void skb_dst_force(struct sk_buff *skb) */ static inline bool dst_hold_safe(struct dst_entry *dst) { - if (dst->flags & DST_NOCACHE) + if (dst->flags & (DST_NOCACHE | DST_NOGC)) return atomic_inc_not_zero(&dst->__refcnt); dst_hold(dst); return true; diff --git a/net/core/dst.c b/net/core/dst.c index 13ba4a090c41..551834c3363f 100644 --- a/net/core/dst.c +++ b/net/core/dst.c @@ -300,18 +300,34 @@ void dst_release(struct dst_entry *dst) { if (dst) { int newrefcnt; - unsigned short nocache = dst->flags & DST_NOCACHE; + unsigned short destroy_after_rcu = dst->flags & + (DST_NOCACHE | DST_NOGC); newrefcnt = atomic_dec_return(&dst->__refcnt); if (unlikely(newrefcnt < 0)) net_warn_ratelimited("%s: dst:%p refcnt:%d\n", __func__, dst, newrefcnt); - if (!newrefcnt && unlikely(nocache)) + if (!newrefcnt && unlikely(destroy_after_rcu)) call_rcu(&dst->rcu_head, dst_destroy_rcu); } } EXPORT_SYMBOL(dst_release); +void dst_release_immediate(struct dst_entry *dst) +{ + if (dst) { + int newrefcnt; + + newrefcnt = atomic_dec_return(&dst->__refcnt); + if (unlikely(newrefcnt < 0)) + net_warn_ratelimited("%s: dst:%p refcnt:%d\n", + __func__, dst, newrefcnt); + if (!newrefcnt) + dst_destroy(dst); + } +} +EXPORT_SYMBOL(dst_release_immediate); + u32 *dst_cow_metrics_generic(struct dst_entry *dst, unsigned long old) { struct dst_metrics *p = kmalloc(sizeof(*p), GFP_ATOMIC);