linux-kernel - Re: [PATCH v3] tracing: add cond_resched to ftrace_replace

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Date:   Tue, 4 Dec 2018 17:32:58 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Anders Roxell <anders.roxell@...aro.org>
Cc:     mingo@...hat.com, catalin.marinas@....com, will.deacon@....com,
        keescook@...omium.org, arnd@...db.de, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v3] tracing: add cond_resched to ftrace_replace_code()

On Tue,  4 Dec 2018 20:40:44 +0100
Anders Roxell <anders.roxell@...aro.org> wrote:

> When running in qemu on an kernel built with allmodconfig and debug
> options (in particular kcov and ubsan) enabled, ftrace_replace_code
> function call take minutes. The ftrace selftest calls
> ftrace_replace_code to look >40000 through
> ftrace_make_call/ftrace_make_nop, and these end up calling
> __aarch64_insn_write/aarch64_insn_patch_text_nosync.
> 
> Microseconds add up because this is called in a loop for each dyn_ftrace
> record, and this triggers the softlockup watchdog unless we let it sleep
> occasionally.
> 
> Rework so that we call cond_resched() if !irqs_disabled() && !preempt_count().

This isn't urgent is it? That is, it doesn't need a stable tag?

-- Steve