From: Glauber Costa <glommer-bzQdu9zFT3WakBO8gow8eQ@public.gmane.org>
To: Linus Torvalds
<torvalds-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>
Cc: Michal Hocko <mhocko-AlSwsSmVLrQ@public.gmane.org>,
linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
devel-GEFAQzZX7r8dnm+yROfE0A@public.gmane.org,
linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org,
cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>,
kamezawa.hiroyu-+CUm20s59erQFUHtdCDX3A@public.gmane.org,
Greg Thelen <gthelen-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>,
Suleiman Souhlal
<suleiman-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>,
Andrew Morton
<akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>
Subject: Re: [PATCH] remove BUG() in possible but rare condition
Date: Wed, 11 Apr 2012 16:02:19 -0300 [thread overview]
Message-ID: <4F85D53B.1070806@parallels.com> (raw)
In-Reply-To: <CA+55aFx1GMWGgh0sTAzvvVSzPQsQ_4NKeaNv1zpKrP4fg1dG+Q-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
On 04/11/2012 03:57 PM, Linus Torvalds wrote:
> On Wed, Apr 11, 2012 at 11:48 AM, Michal Hocko<mhocko-AlSwsSmVLrQ@public.gmane.org> wrote:
>>
>> I am not familiar with the code much but a trivial call chain walk up to
>> write_dev_supers (in btrfs) shows that we do not check for the return value
>> from __getblk so we would nullptr and there might be more.
>> I guess these need some treat before the BUG might be removed, right?
>
> Well, realistically, isn't BUG() as bad as a NULL pointer dereference?
>
> Do you care about the exact message on the screen when your machine dies?
Not particular, but I don't see why (I might be wrong) it would
necessarily lead to a NULL pointer dereference.
At least in my test cases, after turning this to a WARN (to make sure it
was still being hit), the machine could go on just fine.
I was running this in a container system, with restricted memory. After
killing the container - at least in my ext4 system - everything seemed
as happy as ever.
WARNING: multiple messages have this Message-ID (diff)
From: Glauber Costa <glommer@parallels.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Michal Hocko <mhocko@suse.cz>,
linux-kernel@vger.kernel.org, devel@openvz.org,
linux-mm@kvack.org, cgroups@vger.kernel.org,
Johannes Weiner <hannes@cmpxchg.org>,
kamezawa.hiroyu@jp.fujitsu.com, Greg Thelen <gthelen@google.com>,
Suleiman Souhlal <suleiman@google.com>,
Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH] remove BUG() in possible but rare condition
Date: Wed, 11 Apr 2012 16:02:19 -0300 [thread overview]
Message-ID: <4F85D53B.1070806@parallels.com> (raw)
In-Reply-To: <CA+55aFx1GMWGgh0sTAzvvVSzPQsQ_4NKeaNv1zpKrP4fg1dG+Q@mail.gmail.com>
On 04/11/2012 03:57 PM, Linus Torvalds wrote:
> On Wed, Apr 11, 2012 at 11:48 AM, Michal Hocko<mhocko@suse.cz> wrote:
>>
>> I am not familiar with the code much but a trivial call chain walk up to
>> write_dev_supers (in btrfs) shows that we do not check for the return value
>> from __getblk so we would nullptr and there might be more.
>> I guess these need some treat before the BUG might be removed, right?
>
> Well, realistically, isn't BUG() as bad as a NULL pointer dereference?
>
> Do you care about the exact message on the screen when your machine dies?
Not particular, but I don't see why (I might be wrong) it would
necessarily lead to a NULL pointer dereference.
At least in my test cases, after turning this to a WARN (to make sure it
was still being hit), the machine could go on just fine.
I was running this in a container system, with restricted memory. After
killing the container - at least in my ext4 system - everything seemed
as happy as ever.
--
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WARNING: multiple messages have this Message-ID (diff)
From: Glauber Costa <glommer@parallels.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Michal Hocko <mhocko@suse.cz>, <linux-kernel@vger.kernel.org>,
<devel@openvz.org>, <linux-mm@kvack.org>,
<cgroups@vger.kernel.org>, "Johannes Weiner" <hannes@cmpxchg.org>,
<kamezawa.hiroyu@jp.fujitsu.com>,
Greg Thelen <gthelen@google.com>,
Suleiman Souhlal <suleiman@google.com>,
Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH] remove BUG() in possible but rare condition
Date: Wed, 11 Apr 2012 16:02:19 -0300 [thread overview]
Message-ID: <4F85D53B.1070806@parallels.com> (raw)
In-Reply-To: <CA+55aFx1GMWGgh0sTAzvvVSzPQsQ_4NKeaNv1zpKrP4fg1dG+Q@mail.gmail.com>
On 04/11/2012 03:57 PM, Linus Torvalds wrote:
> On Wed, Apr 11, 2012 at 11:48 AM, Michal Hocko<mhocko@suse.cz> wrote:
>>
>> I am not familiar with the code much but a trivial call chain walk up to
>> write_dev_supers (in btrfs) shows that we do not check for the return value
>> from __getblk so we would nullptr and there might be more.
>> I guess these need some treat before the BUG might be removed, right?
>
> Well, realistically, isn't BUG() as bad as a NULL pointer dereference?
>
> Do you care about the exact message on the screen when your machine dies?
Not particular, but I don't see why (I might be wrong) it would
necessarily lead to a NULL pointer dereference.
At least in my test cases, after turning this to a WARN (to make sure it
was still being hit), the machine could go on just fine.
I was running this in a container system, with restricted memory. After
killing the container - at least in my ext4 system - everything seemed
as happy as ever.
next prev parent reply other threads:[~2012-04-11 19:02 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-04-11 18:10 [PATCH] remove BUG() in possible but rare condition Glauber Costa
2012-04-11 18:10 ` Glauber Costa
2012-04-11 18:10 ` Glauber Costa
[not found] ` <1334167824-19142-1-git-send-email-glommer-bzQdu9zFT3WakBO8gow8eQ@public.gmane.org>
2012-04-11 18:48 ` Michal Hocko
2012-04-11 18:48 ` Michal Hocko
2012-04-11 18:48 ` Michal Hocko
[not found] ` <20120411184845.GA24831-VqjxzfR4DlwKmadIfiO5sKVXKuFTiq87@public.gmane.org>
2012-04-11 18:57 ` Linus Torvalds
2012-04-11 18:57 ` Linus Torvalds
2012-04-11 18:57 ` Linus Torvalds
[not found] ` <CA+55aFx1GMWGgh0sTAzvvVSzPQsQ_4NKeaNv1zpKrP4fg1dG+Q-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2012-04-11 19:02 ` Glauber Costa [this message]
2012-04-11 19:02 ` Glauber Costa
2012-04-11 19:02 ` Glauber Costa
[not found] ` <4F85D53B.1070806-bzQdu9zFT3WakBO8gow8eQ@public.gmane.org>
2012-04-11 19:25 ` Michal Hocko
2012-04-11 19:25 ` Michal Hocko
2012-04-11 19:25 ` Michal Hocko
2012-04-11 19:20 ` Michal Hocko
2012-04-11 19:20 ` Michal Hocko
2012-04-11 19:20 ` Michal Hocko
2012-04-11 19:48 ` Don Morris
2012-04-11 21:33 ` Jiri Kosina
2012-04-11 21:33 ` Jiri Kosina
2012-04-11 21:33 ` Jiri Kosina
2012-04-11 18:59 ` Glauber Costa
2012-04-11 18:59 ` Glauber Costa
2012-04-11 18:59 ` Glauber Costa
2012-04-12 9:24 ` Michal Hocko
2012-04-12 9:24 ` Michal Hocko
2012-04-12 9:24 ` Michal Hocko
2012-04-11 20:26 ` Andrew Morton
2012-04-11 20:26 ` Andrew Morton
2012-04-11 20:51 ` Glauber Costa
2012-04-11 20:51 ` Glauber Costa
[not found] ` <4F85EEED.1090906-bzQdu9zFT3WakBO8gow8eQ@public.gmane.org>
2012-04-11 21:12 ` Andrew Morton
2012-04-11 21:12 ` Andrew Morton
2012-04-11 21:12 ` Andrew Morton
[not found] ` <20120411141244.2839d9a8.akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>
2012-04-11 21:26 ` Michal Hocko
2012-04-11 21:26 ` Michal Hocko
2012-04-11 21:26 ` Michal Hocko
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