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Date: Fri, 18 Nov 2022 16:26:34 +0000 From: Mark Rutland <mark.rutland@....com> To: Alexei Starovoitov <alexei.starovoitov@...il.com> Cc: Masami Hiramatsu <mhiramat@...nel.org>, Florent Revest <revest@...omium.org>, bpf <bpf@...r.kernel.org>, Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, Andrii Nakryiko <andrii@...nel.org>, KP Singh <kpsingh@...nel.org>, Brendan Jackman <jackmanb@...gle.com>, markowsky@...gle.com, Steven Rostedt <rostedt@...dmis.org>, Xu Kuohai <xukuohai@...wei.com>, LKML <linux-kernel@...r.kernel.org> Subject: Re: [RFC 0/1] BPF tracing for arm64 using fprobe Hi Alexei, On Thu, Nov 17, 2022 at 08:50:12AM -0800, Alexei Starovoitov wrote: > There might not be a task available where bpf trampoline is running. I'm not sure what you mean by "there might not be a task available"; do you mean that there might not be space in the per-task shadow stack, or that the BPF program can be invoked inan IRQ context? > rcu protection might not be there either. We've spent a lot of time reworking entry/idle sequences with noinstr, so any time BPF can be invoked, we should have a regular kernel environment available, with RCU watching (but not necessarily in an RCU read-side critical section). If BPF is being invoked without RCU watching, that is a bug that needs to be fixed. Do you have a specific example in mind? Thanks, Mark.
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