On 9/15/20 10:40 AM, Jakub Kicinski wrote:
On Tue, 15 Sep 2020 10:35:50 -0700 Yonghong Song wrote:
On 9/15/20 8:33 AM, Jakub Kicinski wrote:
On Mon, 14 Sep 2020 11:46:30 -0700 Yonghong Song wrote:
Currently, we use bucket_lock when traversing bpf_sk_storage_map
elements. Since bpf_iter programs cannot use bpf_sk_storage_get()
and bpf_sk_storage_delete() helpers which may also grab bucket lock,
we do not have a deadlock issue which exists for hashmap when
using bucket_lock ([1]).
If a bucket contains a lot of sockets, during bpf_iter traversing
a bucket, concurrent bpf_sk_storage_{get,delete}() may experience
some undesirable delays. Using rcu_read_lock() is a reasonable
compromise here. Although it may lose some precision, e.g.,
access stale sockets, but it will not hurt performance of other
bpf programs.
[1] https://lore.kernel.org/bpf/20200902235341.2001534-1-yhs@xxxxxx
Cc: Martin KaFai Lau <kafai@xxxxxx>
Signed-off-by: Yonghong Song <yhs@xxxxxx>
Sparse is not happy about it. Could you add some annotations, perhaps?
include/linux/rcupdate.h:686:9: warning: context imbalance in 'bpf_sk_storage_map_seq_find_next' - unexpected unlock
include/linux/rcupdate.h:686:9: warning: context imbalance in 'bpf_sk_storage_map_seq_stop' - unexpected unlock
Okay, I will try.
On my system, sparse is unhappy and core dumped....
/data/users/yhs/work/net-next/include/linux/string.h:12:38: error: too
many errors
/bin/sh: line 1: 2710132 Segmentation fault (core dumped) sparse
-D__linux__ -Dlinux -D__STDC__ -Dunix
-D__unix__ -Wbitwise -Wno-return-void -Wno-unknown-attribute
-D__x86_64__ --arch=x86 -mlittle-endian -m64 -W
p,-MMD,net/core/.bpf_sk_storage.o.d -nostdinc -isystem
...
/data/users/yhs/work/net-next/net/core/bpf_sk_storage.c
make[3]: *** [net/core/bpf_sk_storage.o] Error 139
make[3]: *** Deleting file `net/core/bpf_sk_storage.o'
-bash-4.4$ rpm -qf /bin/sparse
sparse-0.5.2-1.el7.x86_64
-bash-4.4$
I think you need to build from source, sadly :(
https://git.kernel.org/pub/scm//devel/sparse/sparse.git
Indeed, building sparse from source works. After adding some
__releases(RCU) and __acquires(RCU), I now have:
context imbalance in 'bpf_sk_storage_map_seq_find_next' - different
lock contexts for basic block
I may need to restructure code to please sparse...
