From: Petr Mladek <pmladek@suse.com>
To: Waiman Long <longman@redhat.com>
Cc: Vlastimil Babka <vbabka@suse.cz>,
Johannes Weiner <hannes@cmpxchg.org>,
Michal Hocko <mhocko@kernel.org>,
Vladimir Davydov <vdavydov.dev@gmail.com>,
Andrew Morton <akpm@linux-foundation.org>,
Steven Rostedt <rostedt@goodmis.org>,
Sergey Senozhatsky <senozhatsky@chromium.org>,
Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
Rasmus Villemoes <linux@rasmusvillemoes.dk>,
linux-kernel@vger.kernel.org, cgroups@vger.kernel.org,
linux-mm@kvack.org, Ira Weiny <ira.weiny@intel.com>,
Mike Rapoport <rppt@kernel.org>,
David Rientjes <rientjes@google.com>,
Roman Gushchin <guro@fb.com>, Rafael Aquini <aquini@redhat.com>
Subject: Re: [PATCH v4 2/4] mm/page_owner: Use scnprintf() to avoid excessive buffer overrun check
Date: Tue, 8 Feb 2022 11:51:42 +0100 [thread overview]
Message-ID: <YgJLPpUqkTaA298Y@alley> (raw)
In-Reply-To: <42cca916-d4c8-daa1-4a91-60738c499c89@redhat.com>
On Thu 2022-02-03 13:49:02, Waiman Long wrote:
> On 2/3/22 10:46, Vlastimil Babka wrote:
> > On 2/2/22 21:30, Waiman Long wrote:
> > > The snprintf() function can return a length greater than the given
> > > input size. That will require a check for buffer overrun after each
> > > invocation of snprintf(). scnprintf(), on the other hand, will never
> > > return a greater length. By using scnprintf() in selected places, we
> > > can avoid some buffer overrun checks except after stack_depot_snprint()
> > > and after the last snprintf().
> > >
> > > Signed-off-by: Waiman Long <longman@redhat.com>
> > > Acked-by: David Rientjes <rientjes@google.com>
> > > Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
> > Looks like this will work, but note that if the purpose of patch 1/4 was
> > that after the first scnprintf() that overflows the following calls will be
> > short-cut thanks to passing the size as 0, AFAICS that won't work. Because
> > scnprintf() returns the number without trailing zero, 'ret' will be 'count -
> > 1' after the overflow, so 'count - ret' will be 1, never 0.
>
> Yes, I am aware of that. Patch 1 is just a micro-optimization for the very
> rare case.
In theory, we might micro-optimize also the case when "size == 1".
Well, I am not sure if it is worth it. After all, the primary use-case
is to print the message into a big-enough buffer. Lost information is
a bigger problem than the speed ;-)
Best Regards,
Petr
next prev parent reply other threads:[~2022-02-08 11:31 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-01-31 19:23 [PATCH v3 0/4] mm/page_owner: Extend page_owner to show memcg information Waiman Long
2022-01-31 19:23 ` [PATCH v3 1/4] lib/vsprintf: Avoid redundant work with 0 size Waiman Long
2022-01-31 20:42 ` Mike Rapoport
2022-01-31 19:23 ` [PATCH v3 2/4] mm/page_owner: Use scnprintf() to avoid excessive buffer overrun check Waiman Long
2022-01-31 20:38 ` Roman Gushchin
2022-01-31 20:43 ` Mike Rapoport
2022-01-31 19:23 ` [PATCH v3 3/4] mm/page_owner: Print memcg information Waiman Long
2022-01-31 20:51 ` Mike Rapoport
2022-01-31 21:43 ` Waiman Long
2022-02-01 6:23 ` Mike Rapoport
2022-01-31 20:51 ` Roman Gushchin
2022-02-01 10:54 ` Michal Hocko
2022-02-01 17:04 ` Waiman Long
2022-02-02 8:49 ` Michal Hocko
2022-02-02 16:12 ` Waiman Long
2022-01-31 19:23 ` [PATCH v3 4/4] mm/page_owner: Record task command name Waiman Long
2022-01-31 20:54 ` Roman Gushchin
2022-01-31 21:46 ` Waiman Long
2022-01-31 22:03 ` [PATCH v4 " Waiman Long
2022-02-01 15:28 ` Michal Hocko
2022-02-02 16:53 ` Waiman Long
2022-02-03 12:10 ` Vlastimil Babka
2022-02-03 18:53 ` Waiman Long
2022-02-02 20:30 ` [PATCH v4 0/4] mm/page_owner: Extend page_owner to show memcg information Waiman Long
2022-02-02 23:06 ` Rafael Aquini
2022-02-02 20:30 ` [PATCH v4 1/4] lib/vsprintf: Avoid redundant work with 0 size Waiman Long
2022-02-08 10:08 ` Petr Mladek
2022-02-02 20:30 ` [PATCH v4 2/4] mm/page_owner: Use scnprintf() to avoid excessive buffer overrun check Waiman Long
2022-02-03 15:46 ` Vlastimil Babka
2022-02-03 18:49 ` Waiman Long
2022-02-08 10:51 ` Petr Mladek [this message]
2022-02-02 20:30 ` [PATCH v4 3/4] mm/page_owner: Print memcg information Waiman Long
2022-02-03 6:53 ` Mike Rapoport
2022-02-03 12:46 ` Michal Hocko
2022-02-03 19:03 ` Waiman Long
2022-02-07 17:20 ` Michal Hocko
2022-02-07 19:09 ` Andrew Morton
2022-02-07 19:33 ` Waiman Long
2022-02-02 20:30 ` [PATCH v4 4/4] mm/page_owner: Record task command name Waiman Long
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