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From: Miroslav Benes <mbenes@suse.cz>
To: Petr Mladek <pmladek@suse.com>
Cc: Jiri Kosina <jikos@kernel.org>,
	Josh Poimboeuf <jpoimboe@redhat.com>,
	Joe Lawrence <joe.lawrence@redhat.com>,
	Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>,
	live-patching@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/3] livepatch: Remove duplicate warning about missing reliable stacktrace support
Date: Fri, 31 May 2019 15:29:42 +0200 (CEST)	[thread overview]
Message-ID: <alpine.LSU.2.21.1905311528000.742@pobox.suse.cz> (raw)
In-Reply-To: <20190531131906.lkhrfgpze57pqrcg@pathway.suse.cz>

On Fri, 31 May 2019, Petr Mladek wrote:

> On Fri 2019-05-31 14:32:34, Miroslav Benes wrote:
> > On Fri, 31 May 2019, Petr Mladek wrote:
> > 
> > > WARN_ON_ONCE() could not be called safely under rq lock because
> > > of console deadlock issues.
> > > 
> > > It can be simply removed. A better descriptive message is written
> > > in klp_enable_patch() when klp_have_reliable_stack() fails.
> > > The remaining debug message is good enough.
> > > 
> > > Signed-off-by: Petr Mladek <pmladek@suse.com>
> > > ---
> > >  kernel/livepatch/transition.c | 1 -
> > >  1 file changed, 1 deletion(-)
> > > 
> > > diff --git a/kernel/livepatch/transition.c b/kernel/livepatch/transition.c
> > > index abb2a4a2cbb2..1bf362df76e1 100644
> > > --- a/kernel/livepatch/transition.c
> > > +++ b/kernel/livepatch/transition.c
> > > @@ -247,7 +247,6 @@ static int klp_check_stack(struct task_struct *task, char *err_buf)
> > >  	int ret, nr_entries;
> > >  
> > >  	ret = stack_trace_save_tsk_reliable(task, entries, ARRAY_SIZE(entries));
> > > -	WARN_ON_ONCE(ret == -ENOSYS);
> > >  	if (ret < 0) {
> > >  		snprintf(err_buf, STACK_ERR_BUF_SIZE,
> > >  			 "%s: %s:%d has an unreliable stack\n",
> > 
> > The current situation is not the best, but I think the patch improves it 
> > only slightly. I see two possible solutions.
> > 
> > 1. we either revert commit 1d98a69e5cef ("livepatch: Remove reliable 
> > stacktrace check in klp_try_switch_task()"), so that klp_check_stack() 
> > returns right away.
> > 
> > 2. or we test ret from stack_trace_save_tsk_reliable() for ENOSYS and 
> > return.
> > 
> > In my opinion either of them is better than what we have now (and what we 
> > would have with the patch), because klp_check_stack() returns, but it 
> > prints out that a task has an unreliable stack. Yes, it is pr_debug() only 
> > in the end, but still.
> 
> IMHO, any extra check will not improve the situation much. Quiet
> return is as useless as the misleading pr_debug() that will
> not normally get printed anyway.

I disagree here. I think the silent return would be perfectly fine. The 
user was warned in klp_enable_patch() already.

Miroslav

  reply	other threads:[~2019-05-31 13:29 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-31  7:41 [PATCH 0/3] livepatch: Clean up of reliable stacktrace warnings Petr Mladek
2019-05-31  7:41 ` [PATCH 1/3] stacktrace: Remove superfluous WARN_ONCE() from save_stack_trace_tsk_reliable() Petr Mladek
2019-05-31 12:25   ` Miroslav Benes
2019-05-31 19:27     ` Josh Poimboeuf
2019-05-31  7:41 ` [PATCH 2/3] livepatch: Remove duplicate warning about missing reliable stacktrace support Petr Mladek
2019-05-31 12:32   ` Miroslav Benes
2019-05-31 13:19     ` Petr Mladek
2019-05-31 13:29       ` Miroslav Benes [this message]
2019-05-31 19:37     ` Josh Poimboeuf
2019-05-31  7:41 ` [PATCH 3/3] livepatch: Use static buffer for debugging messages under rq lock Petr Mladek
2019-05-31 12:37   ` Miroslav Benes
2019-06-03  8:07     ` Petr Mladek
2019-05-31 19:39   ` Josh Poimboeuf
2019-06-06 13:27     ` Petr Mladek

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