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From: Michael Ellerman <mpe@ellerman.id.au>
To: Jiri Kosina <jkosina@suse.cz>
Cc: Torsten Duwe <duwe@lst.de>,
	ppc-dev <linuxppc-dev@lists.ozlabs.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] ppc64 ftrace: mark data_access callees "notrace" (pt.1)
Date: Tue, 19 May 2015 13:27:07 +1000	[thread overview]
Message-ID: <1432006027.8339.3.camel@ellerman.id.au> (raw)
In-Reply-To: <alpine.LRH.2.00.1505181428360.2306@twin.jikos.cz>

On Mon, 2015-05-18 at 14:29 +0200, Jiri Kosina wrote:
> yOn Sat, 16 May 2015, Torsten Duwe wrote:
> 
> > > > There's got to be a better solution than this.
> > >
> > > Can you think of a better approach?
> > 
> > Maybe a per thread variable to lock out a recursion into tracing?
> > Thanks for your doubt.
> 
> ftrace already handles recursion protection by itself (depending on the 
> per-ftrace-ops FTRACE_OPS_FL_RECURSION_SAFE flag).

OK, so I wonder why that's not working for us?

> It's however not really well-defined what to do when recursion would 
> happen. Therefore __notrace__ annotation, that just completely avoid such 
> situation by making tracing impossible, looks like saner general solution 
> to me.

I disagree. Correctly annotating all functions that might be called ever and
for all time is a maintenance nightmare and is never going to work in the long
term.

cheers



WARNING: multiple messages have this Message-ID (diff)
From: Michael Ellerman <mpe@ellerman.id.au>
To: Jiri Kosina <jkosina@suse.cz>
Cc: ppc-dev <linuxppc-dev@lists.ozlabs.org>,
	Torsten Duwe <duwe@lst.de>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] ppc64 ftrace: mark data_access callees "notrace" (pt.1)
Date: Tue, 19 May 2015 13:27:07 +1000	[thread overview]
Message-ID: <1432006027.8339.3.camel@ellerman.id.au> (raw)
In-Reply-To: <alpine.LRH.2.00.1505181428360.2306@twin.jikos.cz>

On Mon, 2015-05-18 at 14:29 +0200, Jiri Kosina wrote:
> yOn Sat, 16 May 2015, Torsten Duwe wrote:
> 
> > > > There's got to be a better solution than this.
> > >
> > > Can you think of a better approach?
> > 
> > Maybe a per thread variable to lock out a recursion into tracing?
> > Thanks for your doubt.
> 
> ftrace already handles recursion protection by itself (depending on the 
> per-ftrace-ops FTRACE_OPS_FL_RECURSION_SAFE flag).

OK, so I wonder why that's not working for us?

> It's however not really well-defined what to do when recursion would 
> happen. Therefore __notrace__ annotation, that just completely avoid such 
> situation by making tracing impossible, looks like saner general solution 
> to me.

I disagree. Correctly annotating all functions that might be called ever and
for all time is a maintenance nightmare and is never going to work in the long
term.

cheers

  reply	other threads:[~2015-05-19  3:27 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-05-13 16:11 [PATCH] ppc64 ftrace: mark data_access callees "notrace" (pt.1) Torsten Duwe
2015-05-15  1:34 ` Michael Ellerman
2015-05-15  8:45   ` Torsten Duwe
2015-05-16  8:05     ` Torsten Duwe
2015-05-18 12:29       ` Jiri Kosina
2015-05-18 12:29         ` Jiri Kosina
2015-05-19  3:27         ` Michael Ellerman [this message]
2015-05-19  3:27           ` Michael Ellerman
2015-05-19  9:52           ` Jiri Kosina
2015-05-19  9:52             ` Jiri Kosina
2015-06-03 13:02             ` [PATCH 0/4] ppc64 ftrace implementation Torsten Duwe
2015-06-03 13:08               ` [PATCH 1/4] " Torsten Duwe
2015-06-08 15:30                 ` Steven Rostedt
2015-06-08 15:57                   ` Torsten Duwe
2015-06-03 13:10               ` [PATCH 2/4] ppc64 ftrace configuration Torsten Duwe
2015-06-03 13:15               ` [PATCH 3/4] ppc64 ftrace: spare early boot and low level code Torsten Duwe
2015-06-03 13:22               ` [PATCH 4/4] ppc64 ftrace recursion protection Torsten Duwe
2015-05-20  9:03           ` [PATCH] ppc64 ftrace: mark data_access callees "notrace" (pt.1) Torsten Duwe
2015-05-26 14:34             ` Torsten Duwe

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