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Message-ID: <20231004070257.GA311687@alecto.usersys.redhat.com> Date: Wed, 4 Oct 2023 09:02:57 +0200 From: Artem Savkov <asavkov@...hat.com> To: Andrii Nakryiko <andrii.nakryiko@...il.com> Cc: Steven Rostedt <rostedt@...dmis.org>, Masami Hiramatsu <mhiramat@...nel.org>, linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org, Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, Andrii Nakryiko <andrii@...nel.org>, bpf@...r.kernel.org, netdev@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>, linux-rt-users@...r.kernel.org, Jiri Olsa <jolsa@...nel.org> Subject: Re: [RFC PATCH] tracing: change syscall number type in struct syscall_trace_* On Tue, Oct 03, 2023 at 03:11:15PM -0700, Andrii Nakryiko wrote: > On Mon, Oct 2, 2023 at 6:53 AM Artem Savkov <asavkov@...hat.com> wrote: > > > > linux-rt-devel tree contains a patch that adds an extra member to struct > > can you please point to the patch itself that makes that change? Of course, some context would be useful. The patch in question is b1773eac3f29c ("sched: Add support for lazy preemption") from rt-devel tree [0]. It came up a couple of times before: [1] [2] [3] [4]. [0] https://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-rt-devel.git/commit/?id=b1773eac3f29cbdcdfd16e0339f1a164066e9f71 [1] https://lore.kernel.org/linux-rt-users/20200221153541.681468-1-jolsa@kernel.org/t/#u [2] https://github.com/iovisor/bpftrace/commit/a2e3d5dbc03ceb49b776cf5602d31896158844a7 [3] https://lore.kernel.org/bpf/xunyjzy64q9b.fsf@redhat.com/t/#u [4] https://lore.kernel.org/bpf/20230727150647.397626-1-ykaliuta@redhat.com/t/#u > > trace_entry. This causes the offset of args field in struct > > trace_event_raw_sys_enter be different from the one in struct > > syscall_trace_enter: > > > > struct trace_event_raw_sys_enter { > > struct trace_entry ent; /* 0 12 */ > > > > /* XXX last struct has 3 bytes of padding */ > > /* XXX 4 bytes hole, try to pack */ > > > > long int id; /* 16 8 */ > > long unsigned int args[6]; /* 24 48 */ > > /* --- cacheline 1 boundary (64 bytes) was 8 bytes ago --- */ > > char __data[]; /* 72 0 */ > > > > /* size: 72, cachelines: 2, members: 4 */ > > /* sum members: 68, holes: 1, sum holes: 4 */ > > /* paddings: 1, sum paddings: 3 */ > > /* last cacheline: 8 bytes */ > > }; > > > > struct syscall_trace_enter { > > struct trace_entry ent; /* 0 12 */ > > > > /* XXX last struct has 3 bytes of padding */ > > > > int nr; /* 12 4 */ > > long unsigned int args[]; /* 16 0 */ > > > > /* size: 16, cachelines: 1, members: 3 */ > > /* paddings: 1, sum paddings: 3 */ > > /* last cacheline: 16 bytes */ > > }; > > > > This, in turn, causes perf_event_set_bpf_prog() fail while running bpf > > test_profiler testcase because max_ctx_offset is calculated based on the > > former struct, while off on the latter: > > > > 10488 if (is_tracepoint || is_syscall_tp) { > > 10489 int off = trace_event_get_offsets(event->tp_event); > > 10490 > > 10491 if (prog->aux->max_ctx_offset > off) > > 10492 return -EACCES; > > 10493 } > > > > This patch changes the type of nr member in syscall_trace_* structs to > > be long so that "args" offset is equal to that in struct > > trace_event_raw_sys_enter. > > > > Signed-off-by: Artem Savkov <asavkov@...hat.com> > > --- > > kernel/trace/trace.h | 4 ++-- > > kernel/trace/trace_syscalls.c | 7 ++++--- > > 2 files changed, 6 insertions(+), 5 deletions(-) > > > > diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h > > index 77debe53f07cf..cd1d24df85364 100644 > > --- a/kernel/trace/trace.h > > +++ b/kernel/trace/trace.h > > @@ -135,13 +135,13 @@ enum trace_type { > > */ > > struct syscall_trace_enter { > > struct trace_entry ent; > > - int nr; > > + long nr; > > unsigned long args[]; > > }; > > > > struct syscall_trace_exit { > > struct trace_entry ent; > > - int nr; > > + long nr; > > long ret; > > }; > > > > diff --git a/kernel/trace/trace_syscalls.c b/kernel/trace/trace_syscalls.c > > index de753403cdafb..c26939119f2e4 100644 > > --- a/kernel/trace/trace_syscalls.c > > +++ b/kernel/trace/trace_syscalls.c > > @@ -101,7 +101,7 @@ find_syscall_meta(unsigned long syscall) > > return NULL; > > } > > > > -static struct syscall_metadata *syscall_nr_to_meta(int nr) > > +static struct syscall_metadata *syscall_nr_to_meta(long nr) > > { > > if (IS_ENABLED(CONFIG_HAVE_SPARSE_SYSCALL_NR)) > > return xa_load(&syscalls_metadata_sparse, (unsigned long)nr); > > @@ -132,7 +132,8 @@ print_syscall_enter(struct trace_iterator *iter, int flags, > > struct trace_entry *ent = iter->ent; > > struct syscall_trace_enter *trace; > > struct syscall_metadata *entry; > > - int i, syscall; > > + int i; > > + long syscall; > > > > trace = (typeof(trace))ent; > > syscall = trace->nr; > > @@ -177,7 +178,7 @@ print_syscall_exit(struct trace_iterator *iter, int flags, > > struct trace_seq *s = &iter->seq; > > struct trace_entry *ent = iter->ent; > > struct syscall_trace_exit *trace; > > - int syscall; > > + long syscall; > > struct syscall_metadata *entry; > > > > trace = (typeof(trace))ent; > > -- > > 2.41.0 > > > > > -- Artem
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