[PATCH v3] bpf: Fix smp_processor_id() call trace for preemptible kernels

[Edward Adam Davis]

bpf_mem_cache_free_rcu() maybe called in preemptible context, this
will trigger the below warning message:

BUG: using smp_processor_id() in preemptible [00000000] code: syz.0.17/5820
caller is bpf_mem_cache_free_rcu+0x48/0xc0 kernel/bpf/memalloc.c:954
Call Trace:
 check_preemption_disabled+0xd3/0xe0 lib/smp_processor_id.c:47
 bpf_mem_cache_free_rcu+0x48/0xc0 kernel/bpf/memalloc.c:954
 rhtab_delete_elem+0x185a/0x1b30 kernel/bpf/hashtab.c:2969
 __rhtab_map_lookup_and_delete_batch+0x935/0xcb0 kernel/bpf/hashtab.c:3349
 bpf_map_do_batch+0x445/0x630 kernel/bpf/syscall.c:-1
 __sys_bpf+0x906/0xd90 kernel/bpf/syscall.c:-1

this_cpu_ptr() access needs to be guarded against preemption.

Fixes: 5af6807bdb10 ("bpf: Introduce bpf_mem_free_rcu() similar to kfree_rcu().")
Reported-by: syzbot+fd7e415d891073b83e1f@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzkaller.appspot.com/bug?extid=fd7e415d891073b83e1f
Signed-off-by: Edward Adam Davis <eadavis@xxxxxx>
---
v1 -> v2: using guard against preemption
v2 -> v3: replace get/put_cpu() to bpf_disable/enable_instrumentation()

 kernel/bpf/hashtab.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/bpf/hashtab.c b/kernel/bpf/hashtab.c
index 9f394e1aa2e8..d3f2f8a379e8 100644
--- a/kernel/bpf/hashtab.c
+++ b/kernel/bpf/hashtab.c
@@ -3299,6 +3299,7 @@ static int __rhtab_map_lookup_and_delete_batch(struct bpf_map *map,
 	dst_val = values;
 	total = 0;
 
+	bpf_disable_instrumentation();
 	rcu_read_lock();
 
 	/*
@@ -3313,6 +3314,7 @@ static int __rhtab_map_lookup_and_delete_batch(struct bpf_map *map,
 		elem = rhtab_lookup_elem(map, cursor);
 		if (!elem) {
 			rcu_read_unlock();
+			bpf_enable_instrumentation();
 			ret = -EAGAIN;
 			goto free;
 		}
@@ -3350,6 +3352,7 @@ static int __rhtab_map_lookup_and_delete_batch(struct bpf_map *map,
 	}
 
 	rcu_read_unlock();
+	bpf_enable_instrumentation();
 
 	if (total == 0) {
 		ret = -ENOENT;
-- 
2.43.0