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bpf: convert htab map to hlist_nulls

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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>
This commit is contained in:
Alexei Starovoitov 2017-03-07 20:00:13 -08:00 • committed by David S. Miller
parent 9f691549f7
commit 4fe8435909
3 changed files with 79 additions and 34 deletions
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5
include/linux/list_nulls.h
View file

@ -29,6 +29,11 @@ struct hlist_nulls_node {
((ptr)->first = (struct hlist_nulls_node *) NULLS_MARKER(nulls))
#define hlist_nulls_entry(ptr, type, member) container_of(ptr,type,member)
#define hlist_nulls_entry_safe(ptr, type, member) \
({ typeof(ptr) ____ptr = (ptr); \
!is_a_nulls(____ptr) ? hlist_nulls_entry(____ptr, type, member) : NULL; \
})
/**
* ptr_is_a_nulls - Test if a ptr is a nulls
* @ptr: ptr to be tested