From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from lindbergh.monkeyblade.net (lindbergh.monkeyblade.net [23.128.96.19]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 402B8568E for ; Fri, 13 Oct 2023 06:01:46 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="H1u6cRPX" Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2C173BC for ; Thu, 12 Oct 2023 23:01:44 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1697176903; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; 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charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.7 X-Spam-Status: No, score=-2.1 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF, RCVD_IN_DNSWL_BLOCKED,RCVD_IN_MSPIKE_H4,RCVD_IN_MSPIKE_WL, SPF_HELO_NONE,SPF_NONE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net On Thu, Oct 12, 2023 at 04:32:51PM -0700, Andrii Nakryiko wrote: > On Thu, Oct 12, 2023 at 6:43 AM Steven Rostedt wrote: > > > > On Thu, 12 Oct 2023 13:45:50 +0200 > > Artem Savkov wrote: > > > > > linux-rt-devel tree contains a patch (b1773eac3f29c ("sched: Add support > > > for lazy preemption")) that adds an extra member to struct 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 } > > > > > > What bpf program is actually getting is a pointer to struct > > > syscall_tp_t, defined in kernel/trace/trace_syscalls.c. This patch fixes > > > the problem by aligning struct syscall_tp_t with with struct > > > syscall_trace_(enter|exit) and changing the tests to use these structs > > > to dereference context. > > > > > > Signed-off-by: Artem Savkov > > > > I think these changes make sense regardless, can you please resend the > patch without RFC tag so that our CI can run tests for it? Ok, didn't know it was set up like that. > > Thanks for doing a proper fix. > > > > Acked-by: Steven Rostedt (Google) > > But looking at [0] and briefly reading some of the discussions you, > Steven, had. I'm just wondering if it would be best to avoid > increasing struct trace_entry altogether? It seems like preempt_count > is actually a 4-bit field in trace context, so it doesn't seem like we > really need to allocate an entire byte for both preempt_count and > preempt_lazy_count. Why can't we just combine them and not waste 8 > extra bytes for each trace event in a ring buffer? > > [0] https://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-rt-devel.git/commit/?id=b1773eac3f29cbdcdfd16e0339f1a164066e9f71 I agree that avoiding increase in struct trace_entry size would be very desirable, but I have no knowledge whether rt developers had reasons to do it like this. Nevertheless I think the issue with verifier running against a wrong struct still needs to be addressed. -- Regards, Artem