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sched/deadline: Restrict user params max value to 2^63 ns

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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@gmail.com>
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Juri Lelli <juri.lelli@gmail.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: <stable@vger.kernel.org>
Cc: Dario Faggioli<raistlin@linux.it>
Cc: Dave Jones <davej@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/20140513141131.20d944f81633ee937f256385@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Juri Lelli 2014-05-13 14:11:31 +02:00 committed by Ingo Molnar
parent ce5f7f8200
commit b0827819b0
1 changed files with 30 additions and 7 deletions
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37
kernel/sched/core.c
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@ -3195,17 +3195,40 @@ __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;
}
/*