This is a note to let you know that I've just added the patch titled
bpf: bpf_local_storage: Always use bpf_mem_alloc in PREEMPT_RT
to the 6.6-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
bpf-bpf_local_storage-always-use-bpf_mem_alloc-in-pr.patch
and it can be found in the queue-6.6 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 523b95022577339c722da6a8c2b27b83a0a4d817
Author: Martin KaFai Lau <martin.lau@xxxxxxxxxx>
Date: Wed Dec 18 11:30:00 2024 -0800
bpf: bpf_local_storage: Always use bpf_mem_alloc in PREEMPT_RT
[ Upstream commit 8eef6ac4d70eb1f0099fff93321d90ce8fa49ee1 ]
In PREEMPT_RT, kmalloc(GFP_ATOMIC) is still not safe in non preemptible
context. bpf_mem_alloc must be used in PREEMPT_RT. This patch is
to enforce bpf_mem_alloc in the bpf_local_storage when CONFIG_PREEMPT_RT
is enabled.
[ 35.118559] BUG: sleeping function called from invalid context at kernel/locking/spinlock_rt.c:48
[ 35.118566] in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 1832, name: test_progs
[ 35.118569] preempt_count: 1, expected: 0
[ 35.118571] RCU nest depth: 1, expected: 1
[ 35.118577] INFO: lockdep is turned off.
...
[ 35.118647] __might_resched+0x433/0x5b0
[ 35.118677] rt_spin_lock+0xc3/0x290
[ 35.118700] ___slab_alloc+0x72/0xc40
[ 35.118723] __kmalloc_noprof+0x13f/0x4e0
[ 35.118732] bpf_map_kzalloc+0xe5/0x220
[ 35.118740] bpf_selem_alloc+0x1d2/0x7b0
[ 35.118755] bpf_local_storage_update+0x2fa/0x8b0
[ 35.118784] bpf_sk_storage_get_tracing+0x15a/0x1d0
[ 35.118791] bpf_prog_9a118d86fca78ebb_trace_inet_sock_set_state+0x44/0x66
[ 35.118795] bpf_trace_run3+0x222/0x400
[ 35.118820] __bpf_trace_inet_sock_set_state+0x11/0x20
[ 35.118824] trace_inet_sock_set_state+0x112/0x130
[ 35.118830] inet_sk_state_store+0x41/0x90
[ 35.118836] tcp_set_state+0x3b3/0x640
There is no need to adjust the gfp_flags passing to the
bpf_mem_cache_alloc_flags() which only honors the GFP_KERNEL.
The verifier has ensured GFP_KERNEL is passed only in sleepable context.
It has been an old issue since the first introduction of the
bpf_local_storage ~5 years ago, so this patch targets the bpf-next.
bpf_mem_alloc is needed to solve it, so the Fixes tag is set
to the commit when bpf_mem_alloc was first used in the bpf_local_storage.
Fixes: 08a7ce384e33 ("bpf: Use bpf_mem_cache_alloc/free in bpf_local_storage_elem")
Reported-by: Alexei Starovoitov <ast@xxxxxxxxxx>
Signed-off-by: Martin KaFai Lau <martin.lau@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20241218193000.2084281-1-martin.lau@xxxxxxxxx
Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/kernel/bpf/bpf_local_storage.c b/kernel/bpf/bpf_local_storage.c
index e8d02212da703..b4c6b9b3cb421 100644
--- a/kernel/bpf/bpf_local_storage.c
+++ b/kernel/bpf/bpf_local_storage.c
@@ -823,8 +823,12 @@ bpf_local_storage_map_alloc(union bpf_attr *attr,
smap->elem_size = offsetof(struct bpf_local_storage_elem,
sdata.data[attr->value_size]);
- smap->bpf_ma = bpf_ma;
- if (bpf_ma) {
+ /* In PREEMPT_RT, kmalloc(GFP_ATOMIC) is still not safe in non
+ * preemptible context. Thus, enforce all storages to use
+ * bpf_mem_alloc when CONFIG_PREEMPT_RT is enabled.
+ */
+ smap->bpf_ma = IS_ENABLED(CONFIG_PREEMPT_RT) ? true : bpf_ma;
+ if (smap->bpf_ma) {
err = bpf_mem_alloc_init(&smap->selem_ma, smap->elem_size, false);
if (err)
goto free_smap;
