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| author | Daniel T. Lee <danieltimlee@gmail.com> | 2023-08-18 12:01:17 +0300 |
|---|---|---|
| committer | Alexei Starovoitov <ast@kernel.org> | 2023-08-22 01:39:09 +0300 |
| commit | d93a7cf6ca2cfcd7de5d06f753ce8d5e863316ac (patch) | |
| tree | 327fa6cea4d2b66d51367834b8a357955a08c069 /samples | |
| parent | 92632115fb57ff9e368f256913e96d6fd5abf5ab (diff) | |
| download | linux-d93a7cf6ca2cfcd7de5d06f753ce8d5e863316ac.tar.xz | |
samples/bpf: fix broken map lookup probe
In the commit 7c4cd051add3 ("bpf: Fix syscall's stackmap lookup
potential deadlock"), a potential deadlock issue was addressed, which
resulted in *_map_lookup_elem not triggering BPF programs.
(prior to lookup, bpf_disable_instrumentation() is used)
To resolve the broken map lookup probe using "htab_map_lookup_elem",
this commit introduces an alternative approach. Instead, it utilize
"bpf_map_copy_value" and apply a filter specifically for the hash table
with map_type.
Signed-off-by: Daniel T. Lee <danieltimlee@gmail.com>
Fixes: 7c4cd051add3 ("bpf: Fix syscall's stackmap lookup potential deadlock")
Link: https://lore.kernel.org/r/20230818090119.477441-8-danieltimlee@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Diffstat (limited to 'samples')
| -rw-r--r-- | samples/bpf/tracex6.bpf.c | 17 |
1 files changed, 15 insertions, 2 deletions
diff --git a/samples/bpf/tracex6.bpf.c b/samples/bpf/tracex6.bpf.c index 6ad82e68f998..9b23b4737cfb 100644 --- a/samples/bpf/tracex6.bpf.c +++ b/samples/bpf/tracex6.bpf.c @@ -1,6 +1,8 @@ #include "vmlinux.h" #include <linux/version.h> #include <bpf/bpf_helpers.h> +#include <bpf/bpf_tracing.h> +#include <bpf/bpf_core_read.h> struct { __uint(type, BPF_MAP_TYPE_PERF_EVENT_ARRAY); @@ -44,13 +46,24 @@ int bpf_prog1(struct pt_regs *ctx) return 0; } -SEC("kprobe/htab_map_lookup_elem") -int bpf_prog2(struct pt_regs *ctx) +/* + * Since *_map_lookup_elem can't be expected to trigger bpf programs + * due to potential deadlocks (bpf_disable_instrumentation), this bpf + * program will be attached to bpf_map_copy_value (which is called + * from map_lookup_elem) and will only filter the hashtable type. + */ +SEC("kprobe/bpf_map_copy_value") +int BPF_KPROBE(bpf_prog2, struct bpf_map *map) { u32 key = bpf_get_smp_processor_id(); struct bpf_perf_event_value *val, buf; + enum bpf_map_type type; int error; + type = BPF_CORE_READ(map, map_type); + if (type != BPF_MAP_TYPE_HASH) + return 0; + error = bpf_perf_event_read_value(&counters, key, &buf, sizeof(buf)); if (error) return 0; |