KCSAN reported a data-race when accessing node->ref.
Although node->ref does not have to be accurate,
take this chance to use a more common READ_ONCE() and WRITE_ONCE()
pattern instead of data_race().
There is an existing bpf_lru_node_is_ref() and bpf_lru_node_set_ref().
This patch also adds bpf_lru_node_clear_ref() to do the
WRITE_ONCE(node->ref, 0) also.
==================================================================
BUG: KCSAN: data-race in __bpf_lru_list_rotate / __htab_lru_percpu_map_update_elem
write to 0xffff888137038deb of 1 bytes by task 11240 on cpu 1:
__bpf_lru_node_move kernel/bpf/bpf_lru_list.c:113 [inline]
__bpf_lru_list_rotate_active kernel/bpf/bpf_lru_list.c:149 [inline]
__bpf_lru_list_rotate+0x1bf/0x750 kernel/bpf/bpf_lru_list.c:240
bpf_lru_list_pop_free_to_local kernel/bpf/bpf_lru_list.c:329 [inline]
bpf_common_lru_pop_free kernel/bpf/bpf_lru_list.c:447 [inline]
bpf_lru_pop_free+0x638/0xe20 kernel/bpf/bpf_lru_list.c:499
prealloc_lru_pop kernel/bpf/hashtab.c:290 [inline]
__htab_lru_percpu_map_update_elem+0xe7/0x820 kernel/bpf/hashtab.c:1316
bpf_percpu_hash_update+0x5e/0x90 kernel/bpf/hashtab.c:2313
bpf_map_update_value+0x2a9/0x370 kernel/bpf/syscall.c:200
generic_map_update_batch+0x3ae/0x4f0 kernel/bpf/syscall.c:1687
bpf_map_do_batch+0x2d9/0x3d0 kernel/bpf/syscall.c:4534
__sys_bpf+0x338/0x810
__do_sys_bpf kernel/bpf/syscall.c:5096 [inline]
__se_sys_bpf kernel/bpf/syscall.c:5094 [inline]
__x64_sys_bpf+0x43/0x50 kernel/bpf/syscall.c:5094
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x63/0xcd
read to 0xffff888137038deb of 1 bytes by task 11241 on cpu 0:
bpf_lru_node_set_ref kernel/bpf/bpf_lru_list.h:70 [inline]
__htab_lru_percpu_map_update_elem+0x2f1/0x820 kernel/bpf/hashtab.c:1332
bpf_percpu_hash_update+0x5e/0x90 kernel/bpf/hashtab.c:2313
bpf_map_update_value+0x2a9/0x370 kernel/bpf/syscall.c:200
generic_map_update_batch+0x3ae/0x4f0 kernel/bpf/syscall.c:1687
bpf_map_do_batch+0x2d9/0x3d0 kernel/bpf/syscall.c:4534
__sys_bpf+0x338/0x810
__do_sys_bpf kernel/bpf/syscall.c:5096 [inline]
__se_sys_bpf kernel/bpf/syscall.c:5094 [inline]
__x64_sys_bpf+0x43/0x50 kernel/bpf/syscall.c:5094
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x63/0xcd
value changed: 0x01 -> 0x00
Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 11241 Comm: syz-executor.3 Not tainted 6.3.0-rc7-syzkaller-00136-g6a66fdd29ea1 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/30/2023
==================================================================
Reported-by: syzbot+ebe648a84e8784763f82@syzkaller.appspotmail.com
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/r/20230511043748.1384166-1-martin.lau@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
An inclusion of cache.h in printk.h was added in 2014 in commit
c28aa1f0a8 ("printk/cache: mark printk_once test variable
__read_mostly") in order to bring in the definition of __read_mostly. The
usage of __read_mostly was later removed in commit 3ec25826ae ("printk:
Tie printk_once / printk_deferred_once into .data.once for reset") which
made the inclusion of cache.h unnecessary, so remove it.
We have a small amount of code that depended on the inclusion of cache.h
from printk.h; fix that code to include the appropriate header.
This fixes a circular inclusion on arm64 (linux/printk.h -> linux/cache.h
-> asm/cache.h -> linux/kasan-enabled.h -> linux/static_key.h ->
linux/jump_label.h -> linux/bug.h -> asm/bug.h -> linux/printk.h) that
would otherwise be introduced by the next patch.
Build tested using {allyesconfig,defconfig} x {arm64,x86_64}.
Link: https://linux-review.googlesource.com/id/I8fd51f72c9ef1f2d6afd3b2cbc875aa4792c1fba
Link: https://lkml.kernel.org/r/20220427195820.1716975-1-pcc@google.com
Signed-off-by: Peter Collingbourne <pcc@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Konovalov <andreyknvl@gmail.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Based on 1 normalized pattern(s):
this program is free software you can redistribute it and or modify
it under the terms of version 2 of the gnu general public license as
published by the free software foundation
extracted by the scancode license scanner the SPDX license identifier
GPL-2.0-only
has been chosen to replace the boilerplate/reference in 107 file(s).
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Allison Randal <allison@lohutok.net>
Reviewed-by: Richard Fontana <rfontana@redhat.com>
Reviewed-by: Steve Winslow <swinslow@gmail.com>
Reviewed-by: Alexios Zavras <alexios.zavras@intel.com>
Cc: linux-spdx@vger.kernel.org
Link: https://lkml.kernel.org/r/20190528171438.615055994@linutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This patch writes 'node->ref = 1' only if node->ref is 0.
The number of lookups/s for a ~1M entries LRU map increased by
~30% (260097 to 343313).
Other writes on 'node->ref = 0' is not changed. In those cases, the
same cache line has to be changed anyway.
First column: Size of the LRU hash
Second column: Number of lookups/s
Before:
> echo "$((2**20+1)): $(./map_perf_test 1024 1 $((2**20+1)) 10000000 | awk '{print $3}')"
1048577: 260097
After:
> echo "$((2**20+1)): $(./map_perf_test 1024 1 $((2**20+1)) 10000000 | awk '{print $3}')"
1048577: 343313
Signed-off-by: Martin KaFai Lau <kafai@fb.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
Instead of having a common LRU list, this patch allows a
percpu LRU list which can be selected by specifying a map
attribute. The map attribute will be added in the later
patch.
While the common use case for LRU is #reads >> #updates,
percpu LRU list allows bpf prog to absorb unusual #updates
under pathological case (e.g. external traffic facing machine which
could be under attack).
Each percpu LRU is isolated from each other. The LRU nodes (including
free nodes) cannot be moved across different LRU Lists.
Here are the update performance comparison between
common LRU list and percpu LRU list (the test code is
at the last patch):
[root@kerneltest003.31.prn1 ~]# for i in 1 4 8; do echo -n "$i cpus: "; \
./map_perf_test 16 $i | awk '{r += $3}END{print r " updates"}'; done
1 cpus: 2934082 updates
4 cpus: 7391434 updates
8 cpus: 6500576 updates
[root@kerneltest003.31.prn1 ~]# for i in 1 4 8; do echo -n "$i cpus: "; \
./map_perf_test 32 $i | awk '{r += $3}END{printr " updates"}'; done
1 cpus: 2896553 updates
4 cpus: 9766395 updates
8 cpus: 17460553 updates
Signed-off-by: Martin KaFai Lau <kafai@fb.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
Introduce bpf_lru_list which will provide LRU capability to
the bpf_htab in the later patch.
* General Thoughts:
1. Target use case. Read is more often than update.
(i.e. bpf_lookup_elem() is more often than bpf_update_elem()).
If bpf_prog does a bpf_lookup_elem() first and then an in-place
update, it still counts as a read operation to the LRU list concern.
2. It may be useful to think of it as a LRU cache
3. Optimize the read case
3.1 No lock in read case
3.2 The LRU maintenance is only done during bpf_update_elem()
4. If there is a percpu LRU list, it will lose the system-wise LRU
property. A completely isolated percpu LRU list has the best
performance but the memory utilization is not ideal considering
the work load may be imbalance.
5. Hence, this patch starts the LRU implementation with a global LRU
list with batched operations before accessing the global LRU list.
As a LRU cache, #read >> #update/#insert operations, it will work well.
6. There is a local list (for each cpu) which is named
'struct bpf_lru_locallist'. This local list is not used to sort
the LRU property. Instead, the local list is to batch enough
operations before acquiring the lock of the global LRU list. More
details on this later.
7. In the later patch, it allows a percpu LRU list by specifying a
map-attribute for scalability reason and for use cases that need to
prepare for the worst (and pathological) case like DoS attack.
The percpu LRU list is completely isolated from each other and the
LRU nodes (including free nodes) cannot be moved across the list. The
following description is for the global LRU list but mostly applicable
to the percpu LRU list also.
* Global LRU List:
1. It has three sub-lists: active-list, inactive-list and free-list.
2. The two list idea, active and inactive, is borrowed from the
page cache.
3. All nodes are pre-allocated and all sit at the free-list (of the
global LRU list) at the beginning. The pre-allocation reasoning
is similar to the existing BPF_MAP_TYPE_HASH. However,
opting-out prealloc (BPF_F_NO_PREALLOC) is not supported in
the LRU map.
* Active/Inactive List (of the global LRU list):
1. The active list, as its name says it, maintains the active set of
the nodes. We can think of it as the working set or more frequently
accessed nodes. The access frequency is approximated by a ref-bit.
The ref-bit is set during the bpf_lookup_elem().
2. The inactive list, as its name also says it, maintains a less
active set of nodes. They are the candidates to be removed
from the bpf_htab when we are running out of free nodes.
3. The ordering of these two lists is acting as a rough clock.
The tail of the inactive list is the older nodes and
should be released first if the bpf_htab needs free element.
* Rotating the Active/Inactive List (of the global LRU list):
1. It is the basic operation to maintain the LRU property of
the global list.
2. The active list is only rotated when the inactive list is running
low. This idea is similar to the current page cache.
Inactive running low is currently defined as
"# of inactive < # of active".
3. The active list rotation always starts from the tail. It moves
node without ref-bit set to the head of the inactive list.
It moves node with ref-bit set back to the head of the active
list and then clears its ref-bit.
4. The inactive rotation is pretty simply.
It walks the inactive list and moves the nodes back to the head of
active list if its ref-bit is set. The ref-bit is cleared after moving
to the active list.
If the node does not have ref-bit set, it just leave it as it is
because it is already in the inactive list.
* Shrinking the Inactive List (of the global LRU list):
1. Shrinking is the operation to get free nodes when the bpf_htab is
full.
2. It usually only shrinks the inactive list to get free nodes.
3. During shrinking, it will walk the inactive list from the tail,
delete the nodes without ref-bit set from bpf_htab.
4. If no free node found after step (3), it will forcefully get
one node from the tail of inactive or active list. Forcefully is
in the sense that it ignores the ref-bit.
* Local List:
1. Each CPU has a 'struct bpf_lru_locallist'. The purpose is to
batch enough operations before acquiring the lock of the
global LRU.
2. A local list has two sub-lists, free-list and pending-list.
3. During bpf_update_elem(), it will try to get from the free-list
of (the current CPU local list).
4. If the local free-list is empty, it will acquire from the
global LRU list. The global LRU list can either satisfy it
by its global free-list or by shrinking the global inactive
list. Since we have acquired the global LRU list lock,
it will try to get at most LOCAL_FREE_TARGET elements
to the local free list.
5. When a new element is added to the bpf_htab, it will
first sit at the pending-list (of the local list) first.
The pending-list will be flushed to the global LRU list
when it needs to acquire free nodes from the global list
next time.
* Lock Consideration:
The LRU list has a lock (lru_lock). Each bucket of htab has a
lock (buck_lock). If both locks need to be acquired together,
the lock order is always lru_lock -> buck_lock and this only
happens in the bpf_lru_list.c logic.
In hashtab.c, both locks are not acquired together (i.e. one
lock is always released first before acquiring another lock).
Signed-off-by: Martin KaFai Lau <kafai@fb.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
