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net: skb: plumb napi state thru skb freeing paths
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We maintain a NAPI-local cache of skbs which is fed by napi_consume_skb().
Going forward we will also try to cache head and data pages.
Plumb the "are we in a normal NAPI context" information thru
deeper into the freeing path, up to skb_release_data() and
skb_free_head()/skb_pp_recycle(). The "not normal NAPI context"
comes from netpoll which passes budget of 0 to try to reap
the Tx completions but not perform any Rx.

Use "bool napi_safe" rather than bare "int budget",
the further we get from NAPI the more confusing the budget
argument may seem (particularly whether 0 or MAX is the
correct value to pass in when not in NAPI).

Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Tested-by: Dragos Tatulea <dtatulea@nvidia.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
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Jakub Kicinski committed Apr 15, 2023
1 parent c11d2e7 commit b07a2d9
Showing 1 changed file with 20 additions and 18 deletions.
38 changes: 20 additions & 18 deletions net/core/skbuff.c
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Original file line number Diff line number Diff line change
Expand Up @@ -839,7 +839,7 @@ static void skb_clone_fraglist(struct sk_buff *skb)
skb_get(list);
}

static bool skb_pp_recycle(struct sk_buff *skb, void *data)
static bool skb_pp_recycle(struct sk_buff *skb, void *data, bool napi_safe)
{
if (!IS_ENABLED(CONFIG_PAGE_POOL) || !skb->pp_recycle)
return false;
Expand All @@ -856,20 +856,21 @@ static void skb_kfree_head(void *head, unsigned int end_offset)
kfree(head);
}

static void skb_free_head(struct sk_buff *skb)
static void skb_free_head(struct sk_buff *skb, bool napi_safe)
{
unsigned char *head = skb->head;

if (skb->head_frag) {
if (skb_pp_recycle(skb, head))
if (skb_pp_recycle(skb, head, napi_safe))
return;
skb_free_frag(head);
} else {
skb_kfree_head(head, skb_end_offset(skb));
}
}

static void skb_release_data(struct sk_buff *skb, enum skb_drop_reason reason)
static void skb_release_data(struct sk_buff *skb, enum skb_drop_reason reason,
bool napi_safe)
{
struct skb_shared_info *shinfo = skb_shinfo(skb);
int i;
Expand All @@ -894,7 +895,7 @@ static void skb_release_data(struct sk_buff *skb, enum skb_drop_reason reason)
if (shinfo->frag_list)
kfree_skb_list_reason(shinfo->frag_list, reason);

skb_free_head(skb);
skb_free_head(skb, napi_safe);
exit:
/* When we clone an SKB we copy the reycling bit. The pp_recycle
* bit is only set on the head though, so in order to avoid races
Expand Down Expand Up @@ -955,11 +956,12 @@ void skb_release_head_state(struct sk_buff *skb)
}

/* Free everything but the sk_buff shell. */
static void skb_release_all(struct sk_buff *skb, enum skb_drop_reason reason)
static void skb_release_all(struct sk_buff *skb, enum skb_drop_reason reason,
bool napi_safe)
{
skb_release_head_state(skb);
if (likely(skb->head))
skb_release_data(skb, reason);
skb_release_data(skb, reason, napi_safe);
}

/**
Expand All @@ -973,7 +975,7 @@ static void skb_release_all(struct sk_buff *skb, enum skb_drop_reason reason)

void __kfree_skb(struct sk_buff *skb)
{
skb_release_all(skb, SKB_DROP_REASON_NOT_SPECIFIED);
skb_release_all(skb, SKB_DROP_REASON_NOT_SPECIFIED, false);
kfree_skbmem(skb);
}
EXPORT_SYMBOL(__kfree_skb);
Expand Down Expand Up @@ -1027,7 +1029,7 @@ static void kfree_skb_add_bulk(struct sk_buff *skb,
return;
}

skb_release_all(skb, reason);
skb_release_all(skb, reason, false);
sa->skb_array[sa->skb_count++] = skb;

if (unlikely(sa->skb_count == KFREE_SKB_BULK_SIZE)) {
Expand Down Expand Up @@ -1201,7 +1203,7 @@ EXPORT_SYMBOL(consume_skb);
void __consume_stateless_skb(struct sk_buff *skb)
{
trace_consume_skb(skb, __builtin_return_address(0));
skb_release_data(skb, SKB_CONSUMED);
skb_release_data(skb, SKB_CONSUMED, false);
kfree_skbmem(skb);
}

Expand All @@ -1226,7 +1228,7 @@ static void napi_skb_cache_put(struct sk_buff *skb)

void __kfree_skb_defer(struct sk_buff *skb)
{
skb_release_all(skb, SKB_DROP_REASON_NOT_SPECIFIED);
skb_release_all(skb, SKB_DROP_REASON_NOT_SPECIFIED, true);
napi_skb_cache_put(skb);
}

Expand Down Expand Up @@ -1264,7 +1266,7 @@ void napi_consume_skb(struct sk_buff *skb, int budget)
return;
}

skb_release_all(skb, SKB_CONSUMED);
skb_release_all(skb, SKB_CONSUMED, !!budget);
napi_skb_cache_put(skb);
}
EXPORT_SYMBOL(napi_consume_skb);
Expand Down Expand Up @@ -1395,7 +1397,7 @@ EXPORT_SYMBOL_GPL(alloc_skb_for_msg);
*/
struct sk_buff *skb_morph(struct sk_buff *dst, struct sk_buff *src)
{
skb_release_all(dst, SKB_CONSUMED);
skb_release_all(dst, SKB_CONSUMED, false);
return __skb_clone(dst, src);
}
EXPORT_SYMBOL_GPL(skb_morph);
Expand Down Expand Up @@ -2018,9 +2020,9 @@ int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail,
if (skb_has_frag_list(skb))
skb_clone_fraglist(skb);

skb_release_data(skb, SKB_CONSUMED);
skb_release_data(skb, SKB_CONSUMED, false);
} else {
skb_free_head(skb);
skb_free_head(skb, false);
}
off = (data + nhead) - skb->head;

Expand Down Expand Up @@ -6389,12 +6391,12 @@ static int pskb_carve_inside_header(struct sk_buff *skb, const u32 off,
skb_frag_ref(skb, i);
if (skb_has_frag_list(skb))
skb_clone_fraglist(skb);
skb_release_data(skb, SKB_CONSUMED);
skb_release_data(skb, SKB_CONSUMED, false);
} else {
/* we can reuse existing recount- all we did was
* relocate values
*/
skb_free_head(skb);
skb_free_head(skb, false);
}

skb->head = data;
Expand Down Expand Up @@ -6529,7 +6531,7 @@ static int pskb_carve_inside_nonlinear(struct sk_buff *skb, const u32 off,
skb_kfree_head(data, size);
return -ENOMEM;
}
skb_release_data(skb, SKB_CONSUMED);
skb_release_data(skb, SKB_CONSUMED, false);

skb->head = data;
skb->head_frag = 0;
Expand Down

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