From: Michal Hocko <mhocko@suse.cz> To: Rik van Riel <riel@redhat.com> Cc: Andrew Morton <akpm@linux-foundation.org>, Masayoshi Mizuma <m.mizuma@jp.fujitsu.com>, linux-kernel@vger.kernel.org, linux-mm@kvack.org, sandeen@redhat.com, jweiner@redhat.com, kosaki.motohiro@jp.fujitsu.com, fengguang.wu@intel.com, mpatlasov@parallels.com, Motohiro.Kosaki@us.fujitsu.com Subject: Re: [PATCH v5] mm,writeback: fix divide by zero in pos_ratio_polynom Date: Fri, 2 May 2014 11:16:41 +0200 [thread overview] Message-ID: <20140502091641.GB3446@dhcp22.suse.cz> (raw) In-Reply-To: <20140430164255.7a753a8e@cuia.bos.redhat.com> On Wed 30-04-14 16:42:55, Rik van Riel wrote: > On Wed, 30 Apr 2014 13:13:53 -0700 > Andrew Morton <akpm@linux-foundation.org> wrote: > > > This was a consequence of 64->32 truncation and it can't happen any > > more, can it? > > Andrew, this is cleaner indeed :) > > Masayoshi-san, does the bug still happen with this version, or does > this fix the problem? > > ---8<--- > > Subject: mm,writeback: fix divide by zero in pos_ratio_polynom > > It is possible for "limit - setpoint + 1" to equal zero, after > getting truncated to a 32 bit variable, and resulting in a divide > by zero error. > > Using the fully 64 bit divide functions avoids this problem. > > Also uninline pos_ratio_polynom, at Andrew's request. > > Signed-off-by: Rik van Riel <riel@redhat.com> This looks much better. Reviewed-by: Michal Hocko <mhocko@suse.cz> > --- > mm/page-writeback.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/mm/page-writeback.c b/mm/page-writeback.c > index ef41349..a4317da 100644 > --- a/mm/page-writeback.c > +++ b/mm/page-writeback.c > @@ -593,14 +593,14 @@ unsigned long bdi_dirty_limit(struct backing_dev_info *bdi, unsigned long dirty) > * (5) the closer to setpoint, the smaller |df/dx| (and the reverse) > * => fast response on large errors; small oscillation near setpoint > */ > -static inline long long pos_ratio_polynom(unsigned long setpoint, > +static long long pos_ratio_polynom(unsigned long setpoint, > unsigned long dirty, > unsigned long limit) > { > long long pos_ratio; > long x; > > - x = div_s64(((s64)setpoint - (s64)dirty) << RATELIMIT_CALC_SHIFT, > + x = div64_s64(((s64)setpoint - (s64)dirty) << RATELIMIT_CALC_SHIFT, > limit - setpoint + 1); > pos_ratio = x; > pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT; > @@ -842,7 +842,7 @@ static unsigned long bdi_position_ratio(struct backing_dev_info *bdi, > x_intercept = bdi_setpoint + span; > > if (bdi_dirty < x_intercept - span / 4) { > - pos_ratio = div_u64(pos_ratio * (x_intercept - bdi_dirty), > + pos_ratio = div64_u64(pos_ratio * (x_intercept - bdi_dirty), > x_intercept - bdi_setpoint + 1); > } else > pos_ratio /= 4; > -- Michal Hocko SUSE Labs
WARNING: multiple messages have this Message-ID (diff)
From: Michal Hocko <mhocko@suse.cz> To: Rik van Riel <riel@redhat.com> Cc: Andrew Morton <akpm@linux-foundation.org>, Masayoshi Mizuma <m.mizuma@jp.fujitsu.com>, linux-kernel@vger.kernel.org, linux-mm@kvack.org, sandeen@redhat.com, jweiner@redhat.com, kosaki.motohiro@jp.fujitsu.com, fengguang.wu@intel.com, mpatlasov@parallels.com, Motohiro.Kosaki@us.fujitsu.com Subject: Re: [PATCH v5] mm,writeback: fix divide by zero in pos_ratio_polynom Date: Fri, 2 May 2014 11:16:41 +0200 [thread overview] Message-ID: <20140502091641.GB3446@dhcp22.suse.cz> (raw) In-Reply-To: <20140430164255.7a753a8e@cuia.bos.redhat.com> On Wed 30-04-14 16:42:55, Rik van Riel wrote: > On Wed, 30 Apr 2014 13:13:53 -0700 > Andrew Morton <akpm@linux-foundation.org> wrote: > > > This was a consequence of 64->32 truncation and it can't happen any > > more, can it? > > Andrew, this is cleaner indeed :) > > Masayoshi-san, does the bug still happen with this version, or does > this fix the problem? > > ---8<--- > > Subject: mm,writeback: fix divide by zero in pos_ratio_polynom > > It is possible for "limit - setpoint + 1" to equal zero, after > getting truncated to a 32 bit variable, and resulting in a divide > by zero error. > > Using the fully 64 bit divide functions avoids this problem. > > Also uninline pos_ratio_polynom, at Andrew's request. > > Signed-off-by: Rik van Riel <riel@redhat.com> This looks much better. Reviewed-by: Michal Hocko <mhocko@suse.cz> > --- > mm/page-writeback.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/mm/page-writeback.c b/mm/page-writeback.c > index ef41349..a4317da 100644 > --- a/mm/page-writeback.c > +++ b/mm/page-writeback.c > @@ -593,14 +593,14 @@ unsigned long bdi_dirty_limit(struct backing_dev_info *bdi, unsigned long dirty) > * (5) the closer to setpoint, the smaller |df/dx| (and the reverse) > * => fast response on large errors; small oscillation near setpoint > */ > -static inline long long pos_ratio_polynom(unsigned long setpoint, > +static long long pos_ratio_polynom(unsigned long setpoint, > unsigned long dirty, > unsigned long limit) > { > long long pos_ratio; > long x; > > - x = div_s64(((s64)setpoint - (s64)dirty) << RATELIMIT_CALC_SHIFT, > + x = div64_s64(((s64)setpoint - (s64)dirty) << RATELIMIT_CALC_SHIFT, > limit - setpoint + 1); > pos_ratio = x; > pos_ratio = pos_ratio * x >> RATELIMIT_CALC_SHIFT; > @@ -842,7 +842,7 @@ static unsigned long bdi_position_ratio(struct backing_dev_info *bdi, > x_intercept = bdi_setpoint + span; > > if (bdi_dirty < x_intercept - span / 4) { > - pos_ratio = div_u64(pos_ratio * (x_intercept - bdi_dirty), > + pos_ratio = div64_u64(pos_ratio * (x_intercept - bdi_dirty), > x_intercept - bdi_setpoint + 1); > } else > pos_ratio /= 4; > -- Michal Hocko SUSE Labs -- 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:[~2014-05-02 9:16 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 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 [this message] 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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