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perf offcpu: Fix build failure on old kernels 

Old kernels have a 'struct task_struct' which contains a "state" field
and newer kernels have "__state" instead.

While the get_task_state() in the BPF code handles that in some way, it
assumed the current kernel has the new definition and it caused a build
error on old kernels.

We should not assume anything and access them carefully.  Do not use
'task struct' directly access it instead using new and old definitions
in a row.

Fixes: edc41a1099 ("perf record: Enable off-cpu analysis with BPF")
Reported-by: Ian Rogers <irogers@google.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Cc: Blake Jones <blakejones@google.com>
Cc: Hao Luo <haoluo@google.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Milian Wolff <milian.wolff@kdab.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Song Liu <songliubraving@fb.com>
Cc: bpf@vger.kernel.org
Link: http://lore.kernel.org/lkml/20220624231313.367909-2-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
This commit is contained in:
Namhyung Kim 2022-06-24 16:13:08 -07:00 committed by Arnaldo Carvalho de Melo
parent 941e3e7912
commit d6838ec44b
1 changed files with 14 additions and 6 deletions
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16
tools/perf/util/bpf_skel/off_cpu.bpf.c
View File

@ -71,6 +71,11 @@ struct {
__uint(max_entries, 1);
} cgroup_filter SEC(".maps");
/* new kernel task_struct definition */
struct task_struct___new {
long __state;
} __attribute__((preserve_access_index));
/* old kernel task_struct definition */
struct task_struct___old {
long state;
@ -93,14 +98,17 @@ const volatile bool uses_cgroup_v1 = false;
*/
static inline int get_task_state(struct task_struct *t)
{
if (bpf_core_field_exists(t->__state))
return BPF_CORE_READ(t, __state);
/* recast pointer to capture new type for compiler */
struct task_struct___new *t_new = (void *)t;
/* recast pointer to capture task_struct___old type for compiler */
if (bpf_core_field_exists(t_new->__state)) {
return BPF_CORE_READ(t_new, __state);
} else {
/* recast pointer to capture old type for compiler */
struct task_struct___old *t_old = (void *)t;
/* now use old "state" name of the field */
return BPF_CORE_READ(t_old, state);
}
}
static inline __u64 get_cgroup_id(struct task_struct *t)