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Message-Id: <20140513141131.20d944f81633ee937f256385@gmail.com>
Date: Tue, 13 May 2014 14:11:31 +0200
From: Juri Lelli <juri.lelli@...il.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: "Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>,
Dario Faggioli <raistlin@...ux.it>,
Ingo Molnar <mingo@...e.hu>,
lkml <linux-kernel@...r.kernel.org>,
Dave Jones <davej@...hat.com>
Subject: Re: [BUG] sched_setattr() SCHED_DEADLINE hangs system
On Tue, 13 May 2014 12:43:07 +0200
Peter Zijlstra <peterz@...radead.org> wrote:
> On Tue, May 13, 2014 at 11:57:49AM +0200, Juri Lelli wrote:
> > static bool
> > __checkparam_dl(const struct sched_attr *attr)
> > {
> > return attr && attr->sched_deadline != 0 &&
> > (attr->sched_period == 0 ||
> > - (s64)(attr->sched_period - attr->sched_deadline) >= 0) &&
> > - (s64)(attr->sched_deadline - attr->sched_runtime ) >= 0 &&
> > - attr->sched_runtime >= (2 << (DL_SCALE - 1));
> > + (attr->sched_period >= attr->sched_deadline)) &&
> > + (attr->sched_deadline >= attr->sched_runtime) &&
> > + attr->sched_runtime >= (1ULL << DL_SCALE) &&
> > + (attr->sched_deadline < (1ULL << 63) &&
> > + attr->sched_period < (1ULL << 63));
> > }
>
> Could we maybe rewrite that function to look less like a ioccc.org
> submission?
>
Right.
> static bool
> __checkparam_dl(const struct sched_attr *attr)
> {
> if (!attr) /* possible at all? */
> return false;
>
I'd say no, removed.
> /* runtime <= deadline <= period */
> if (attr->sched_period < attr->sched_deadline ||
> attr->sched_deadline < attr->sched_runtime)
> return false;
>
> /*
> * Since we truncate DL_SCALE bits make sure we're at least that big,
> * if runtime > (1 << DL_SCALE), so must the others be per the above
> */
> if (attr->sched_runtime <= (1ULL << DL_SCALE))
> return false;
>
> /*
> * Since we use the MSB for wrap-around and sign issues, make
> * sure its not set, if period < 2^63, so must the others be.
> */
> if (attr->sched_period & (1ULL << 63))
> return false;
>
> return true;
> }
>
> Did I miss anything?
period can be 0, so we have to check also sched_deadline for MSB set.
Thanks,
- Juri
---
>From e0c44d7614127f8dfbafc08c30681cb8098271e8 Mon Sep 17 00:00:00 2001
From: Juri Lelli <juri.lelli@...il.com>
Date: Tue, 13 May 2014 10:15:59 +0200
Subject: [PATCH] sched/deadline: restrict user params max value to 2^63 ns
Michael Kerrisk noticed that creating SCHED_DEADLINE reservations
with certain parameters (e.g, a runtime of something near 2^64 ns)
can cause a system freeze for some amount of time.
The problem is that in the interface we have
u64 sched_runtime;
while internally we need to have a signed runtime (to cope with
budget overruns)
s64 runtime;
At the time we setup a new dl_entity we copy the first value in
the second. The cast turns out with negative values when
sched_runtime is too big, and this causes the scheduler to go crazy
right from the start.
Moreover, considering how we deal with deadlines wraparound
(s64)(a - b) < 0
we also have to restrict acceptable values for sched_{deadline,period}.
This patch fixes the thing checking that user parameters are always
below 2^63 ns (still large enough for everyone).
It also rewrites other conditions that we check, since in
__checkparam_dl we don't have to deal with deadline wraparounds
and what we have now erroneously fails when the difference between
values is too big.
Reported-by: Michael Kerrisk <mtk.manpages@...il.com>
Suggested-by: Peter Zijlstra <peterz@...radead.org>
Signed-off-by: Juri Lelli <juri.lelli@...il.com>
---
kernel/sched/core.c | 37 ++++++++++++++++++++++++++++++-------
1 file changed, 30 insertions(+), 7 deletions(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index d9d8ece..682a986 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3188,17 +3188,40 @@ __getparam_dl(struct task_struct *p, struct sched_attr *attr)
* We ask for the deadline not being zero, and greater or equal
* than the runtime, as well as the period of being zero or
* greater than deadline. Furthermore, we have to be sure that
- * user parameters are above the internal resolution (1us); we
- * check sched_runtime only since it is always the smaller one.
+ * user parameters are above the internal resolution of 1us (we
+ * check sched_runtime only since it is always the smaller one) and
+ * below 2^63 ns (we have to check both sched_deadline and
+ * sched_period, as the latter can be zero).
*/
static bool
__checkparam_dl(const struct sched_attr *attr)
{
- return attr && attr->sched_deadline != 0 &&
- (attr->sched_period == 0 ||
- (s64)(attr->sched_period - attr->sched_deadline) >= 0) &&
- (s64)(attr->sched_deadline - attr->sched_runtime ) >= 0 &&
- attr->sched_runtime >= (2 << (DL_SCALE - 1));
+ /* deadline != 0 */
+ if (attr->sched_deadline == 0)
+ return false;
+
+ /*
+ * Since we truncate DL_SCALE bits, make sure we're at least
+ * that big.
+ */
+ if (attr->sched_runtime < (1ULL << DL_SCALE))
+ return false;
+
+ /*
+ * Since we use the MSB for wrap-around and sign issues, make
+ * sure it's not set (mind that period can be equal to zero).
+ */
+ if (attr->sched_deadline & (1ULL << 63) ||
+ attr->sched_period & (1ULL << 63))
+ return false;
+
+ /* runtime <= deadline <= period (if period != 0) */
+ if ((attr->sched_period != 0 &&
+ attr->sched_period < attr->sched_deadline) ||
+ attr->sched_deadline < attr->sched_runtime)
+ return false;
+
+ return true;
}
/*
--
1.7.9.5
--
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