linux-kernel - Re: [PATCH v7 1/4] ftrace: Implement fs notification for tracing_max

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Message-ID: <20191002185043.298fa820@gandalf.local.home>
Date:   Wed, 2 Oct 2019 18:50:43 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Viktor Rosendahl <viktor.rosendahl@...il.com>
Cc:     Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        Joel Fernandes <joel@...lfernandes.org>
Subject: Re: [PATCH v7 1/4] ftrace: Implement fs notification for
 tracing_max_latency

On Thu, 3 Oct 2019 00:04:56 +0200
Viktor Rosendahl <viktor.rosendahl@...il.com> wrote:

> > Can fsnotify() be called from irq context? If so, why have the work
> > queue at all? Just do the work from the irq_work handler.
> >   
> 
> fsnotify() might sleep. It calls send_to_group(), which calls 
> inotify_handle_event() through a function pointer.
> 
> inotify_handle_event() calls kmalloc() without the GFP_ATOMIC flag.
> 
> There might be other reasons as well but the above is one that I have 
> seen a warning for, when enabling CONFIG_DEBUG_ATOMIC_SLEEP and trying 
> to call fsnotify() from an atomic context.

Thanks for the context. I wonder if we should add a "might_sleep()" to
fsnotify() then.

-- Steve