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4fe8435909
when all map elements are pre-allocated one cpu can delete and reuse htab_elem
while another cpu is still walking the hlist. In such case the lookup may
miss the element. Convert hlist to hlist_nulls to avoid such scenario.
When bucket lock is taken there is no need to take such precautions,
so only convert map_lookup and map_get_next to nulls.
The race window is extremely small and only reproducible with explicit
udelay() inside lookup_nulls_elem_raw()
Similar to hlist add hlist_nulls_for_each_entry_safe() and
hlist_nulls_entry_safe() helpers.
Fixes: 6c90598174 ("bpf: pre-allocate hash map elements")
Reported-by: Jonathan Perry <jonperry@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
123 lines
3.4 KiB
C
123 lines
3.4 KiB
C
#ifndef _LINUX_LIST_NULLS_H
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#define _LINUX_LIST_NULLS_H
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#include <linux/poison.h>
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#include <linux/const.h>
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/*
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* Special version of lists, where end of list is not a NULL pointer,
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* but a 'nulls' marker, which can have many different values.
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* (up to 2^31 different values guaranteed on all platforms)
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*
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* In the standard hlist, termination of a list is the NULL pointer.
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* In this special 'nulls' variant, we use the fact that objects stored in
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* a list are aligned on a word (4 or 8 bytes alignment).
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* We therefore use the last significant bit of 'ptr' :
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* Set to 1 : This is a 'nulls' end-of-list marker (ptr >> 1)
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* Set to 0 : This is a pointer to some object (ptr)
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*/
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struct hlist_nulls_head {
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struct hlist_nulls_node *first;
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};
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struct hlist_nulls_node {
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struct hlist_nulls_node *next, **pprev;
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};
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#define NULLS_MARKER(value) (1UL | (((long)value) << 1))
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#define INIT_HLIST_NULLS_HEAD(ptr, nulls) \
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((ptr)->first = (struct hlist_nulls_node *) NULLS_MARKER(nulls))
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#define hlist_nulls_entry(ptr, type, member) container_of(ptr,type,member)
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#define hlist_nulls_entry_safe(ptr, type, member) \
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({ typeof(ptr) ____ptr = (ptr); \
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!is_a_nulls(____ptr) ? hlist_nulls_entry(____ptr, type, member) : NULL; \
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})
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/**
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* ptr_is_a_nulls - Test if a ptr is a nulls
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* @ptr: ptr to be tested
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*
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*/
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static inline int is_a_nulls(const struct hlist_nulls_node *ptr)
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{
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return ((unsigned long)ptr & 1);
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}
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/**
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* get_nulls_value - Get the 'nulls' value of the end of chain
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* @ptr: end of chain
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*
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* Should be called only if is_a_nulls(ptr);
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*/
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static inline unsigned long get_nulls_value(const struct hlist_nulls_node *ptr)
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{
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return ((unsigned long)ptr) >> 1;
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}
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static inline int hlist_nulls_unhashed(const struct hlist_nulls_node *h)
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{
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return !h->pprev;
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}
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static inline int hlist_nulls_empty(const struct hlist_nulls_head *h)
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{
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return is_a_nulls(READ_ONCE(h->first));
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}
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static inline void hlist_nulls_add_head(struct hlist_nulls_node *n,
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struct hlist_nulls_head *h)
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{
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struct hlist_nulls_node *first = h->first;
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n->next = first;
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n->pprev = &h->first;
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h->first = n;
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if (!is_a_nulls(first))
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first->pprev = &n->next;
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}
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static inline void __hlist_nulls_del(struct hlist_nulls_node *n)
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{
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struct hlist_nulls_node *next = n->next;
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struct hlist_nulls_node **pprev = n->pprev;
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WRITE_ONCE(*pprev, next);
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if (!is_a_nulls(next))
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next->pprev = pprev;
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}
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static inline void hlist_nulls_del(struct hlist_nulls_node *n)
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{
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__hlist_nulls_del(n);
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n->pprev = LIST_POISON2;
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}
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/**
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* hlist_nulls_for_each_entry - iterate over list of given type
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* @tpos: the type * to use as a loop cursor.
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* @pos: the &struct hlist_node to use as a loop cursor.
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* @head: the head for your list.
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* @member: the name of the hlist_node within the struct.
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*
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*/
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#define hlist_nulls_for_each_entry(tpos, pos, head, member) \
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for (pos = (head)->first; \
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(!is_a_nulls(pos)) && \
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({ tpos = hlist_nulls_entry(pos, typeof(*tpos), member); 1;}); \
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pos = pos->next)
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/**
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* hlist_nulls_for_each_entry_from - iterate over a hlist continuing from current point
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* @tpos: the type * to use as a loop cursor.
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* @pos: the &struct hlist_node to use as a loop cursor.
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* @member: the name of the hlist_node within the struct.
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*
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*/
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#define hlist_nulls_for_each_entry_from(tpos, pos, member) \
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for (; (!is_a_nulls(pos)) && \
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({ tpos = hlist_nulls_entry(pos, typeof(*tpos), member); 1;}); \
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pos = pos->next)
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#endif
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