From: Andrew Morton <akpm@linux-foundation.org> To: Rik van Riel <riel@redhat.com> Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, sandeen@redhat.com, jweiner@redhat.com, kosaki.motohiro@jp.fujitsu.com, mhocko@suse.cz, fengguang.wu@intel.com, mpatlasov@parallels.com Subject: Re: [PATCH] mm,writeback: fix divide by zero in pos_ratio_polynom Date: Tue, 29 Apr 2014 15:39:36 -0700 [thread overview] Message-ID: <20140429153936.49a2710c0c2bba4d233032f2@linux-foundation.org> (raw) In-Reply-To: <20140429151910.53f740ef@annuminas.surriel.com> On Tue, 29 Apr 2014 15:19:10 -0400 Rik van Riel <riel@redhat.com> wrote: > It is possible for "limit - setpoint + 1" to equal zero, leading to a > divide by zero error. Blindly adding 1 to "limit - setpoint" is not > working, so we need to actually test the divisor before calling div64. > > ... > > --- a/mm/page-writeback.c > +++ b/mm/page-writeback.c > @@ -597,11 +597,16 @@ static inline long long pos_ratio_polynom(unsigned long setpoint, > unsigned long dirty, > unsigned long limit) > { > + unsigned int divisor; I'm thinking this would be better as a ulong so I don't have to worry my pretty head over truncation things? > long long pos_ratio; > long x; > > + divisor = limit - setpoint; > + if (!divisor) > + divisor = 1; > + > x = div_s64(((s64)setpoint - (s64)dirty) << RATELIMIT_CALC_SHIFT, > - limit - setpoint + 1); > + divisor); > pos_ratio = x; > pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT; > pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT; --- a/mm/page-writeback.c~mm-page-writebackc-fix-divide-by-zero-in-pos_ratio_polynom-fix +++ a/mm/page-writeback.c @@ -597,13 +597,13 @@ static inline long long pos_ratio_polyno unsigned long dirty, unsigned long limit) { - unsigned int divisor; + unsigned long divisor; long long pos_ratio; long x; divisor = limit - setpoint; if (!divisor) - divisor = 1; + divisor = 1; /* Avoid div-by-zero */ x = div_s64(((s64)setpoint - (s64)dirty) << RATELIMIT_CALC_SHIFT, divisor); _
WARNING: multiple messages have this Message-ID (diff)
From: Andrew Morton <akpm@linux-foundation.org> To: Rik van Riel <riel@redhat.com> Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, sandeen@redhat.com, jweiner@redhat.com, kosaki.motohiro@jp.fujitsu.com, mhocko@suse.cz, fengguang.wu@intel.com, mpatlasov@parallels.com Subject: Re: [PATCH] mm,writeback: fix divide by zero in pos_ratio_polynom Date: Tue, 29 Apr 2014 15:39:36 -0700 [thread overview] Message-ID: <20140429153936.49a2710c0c2bba4d233032f2@linux-foundation.org> (raw) In-Reply-To: <20140429151910.53f740ef@annuminas.surriel.com> On Tue, 29 Apr 2014 15:19:10 -0400 Rik van Riel <riel@redhat.com> wrote: > It is possible for "limit - setpoint + 1" to equal zero, leading to a > divide by zero error. Blindly adding 1 to "limit - setpoint" is not > working, so we need to actually test the divisor before calling div64. > > ... > > --- a/mm/page-writeback.c > +++ b/mm/page-writeback.c > @@ -597,11 +597,16 @@ static inline long long pos_ratio_polynom(unsigned long setpoint, > unsigned long dirty, > unsigned long limit) > { > + unsigned int divisor; I'm thinking this would be better as a ulong so I don't have to worry my pretty head over truncation things? > long long pos_ratio; > long x; > > + divisor = limit - setpoint; > + if (!divisor) > + divisor = 1; > + > x = div_s64(((s64)setpoint - (s64)dirty) << RATELIMIT_CALC_SHIFT, > - limit - setpoint + 1); > + divisor); > pos_ratio = x; > pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT; > pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT; --- a/mm/page-writeback.c~mm-page-writebackc-fix-divide-by-zero-in-pos_ratio_polynom-fix +++ a/mm/page-writeback.c @@ -597,13 +597,13 @@ static inline long long pos_ratio_polyno unsigned long dirty, unsigned long limit) { - unsigned int divisor; + unsigned long divisor; long long pos_ratio; long x; divisor = limit - setpoint; if (!divisor) - divisor = 1; + divisor = 1; /* Avoid div-by-zero */ x = div_s64(((s64)setpoint - (s64)dirty) << RATELIMIT_CALC_SHIFT, divisor); _ -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
next prev parent reply other threads:[~2014-04-29 22:39 UTC|newest] Thread overview: 56+ messages / expand[flat|nested] mbox.gz Atom feed top 2014-04-29 19:19 [PATCH] mm,writeback: fix divide by zero in pos_ratio_polynom Rik van Riel 2014-04-29 19:19 ` Rik van Riel 2014-04-29 19:43 ` Motohiro Kosaki 2014-04-29 19:43 ` Motohiro Kosaki 2014-04-29 22:39 ` Andrew Morton [this message] 2014-04-29 22:39 ` Andrew Morton 2014-04-29 22:48 ` Rik van Riel 2014-04-29 22:48 ` Rik van Riel 2014-04-29 22:53 ` Andrew Morton 2014-04-29 22:53 ` Andrew Morton 2014-04-30 8:04 ` Maxim Patlasov 2014-04-30 8:04 ` Maxim Patlasov 2014-04-30 8:12 ` Michal Hocko 2014-04-30 8:12 ` Michal Hocko 2014-04-30 8:34 ` Maxim Patlasov 2014-04-30 8:34 ` Maxim Patlasov 2014-04-30 10:01 ` Masayoshi Mizuma 2014-04-30 10:01 ` Masayoshi Mizuma 2014-04-30 13:30 ` [PATCH v2] " Rik van Riel 2014-04-30 13:30 ` Rik van Riel 2014-04-30 13:48 ` Michal Hocko 2014-04-30 13:48 ` Michal Hocko 2014-04-30 14:26 ` Rik van Riel 2014-04-30 14:26 ` Rik van Riel 2014-04-30 14:31 ` Rik van Riel 2014-04-30 14:31 ` Rik van Riel 2014-04-30 14:49 ` Michal Hocko 2014-04-30 14:49 ` Michal Hocko 2014-04-30 14:52 ` Rik van Riel 2014-04-30 14:52 ` Rik van Riel 2014-04-30 14:41 ` [PATCH v3] " Rik van Riel 2014-04-30 14:41 ` Rik van Riel 2014-04-30 19:00 ` Andrew Morton 2014-04-30 19:00 ` Andrew Morton 2014-04-30 19:30 ` Rik van Riel 2014-04-30 19:30 ` Rik van Riel 2014-04-30 19:35 ` Andrew Morton 2014-04-30 19:35 ` Andrew Morton 2014-04-30 20:02 ` [PATCH v4] " Rik van Riel 2014-04-30 20:02 ` Rik van Riel 2014-04-30 20:13 ` Andrew Morton 2014-04-30 20:13 ` Andrew Morton 2014-04-30 20:32 ` Rik van Riel 2014-04-30 20:32 ` Rik van Riel 2014-04-30 20:42 ` [PATCH v5] " Rik van Riel 2014-04-30 20:42 ` Rik van Riel 2014-04-30 21:00 ` Andrew Morton 2014-04-30 21:00 ` Andrew Morton 2014-04-30 21:21 ` Rik van Riel 2014-04-30 21:21 ` Rik van Riel 2014-04-30 21:32 ` Andrew Morton 2014-04-30 21:32 ` Andrew Morton 2014-05-02 9:16 ` Michal Hocko 2014-05-02 9:16 ` Michal Hocko 2014-05-08 10:17 ` Masayoshi Mizuma 2014-05-08 10:17 ` Masayoshi Mizuma
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