Messages in this thread Patch in this message | | | Date | Tue, 13 May 2014 14:11:31 +0200 | From | Juri Lelli <> | Subject | Re: [BUG] sched_setattr() SCHED_DEADLINE hangs system |
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On Tue, 13 May 2014 12:43:07 +0200 Peter Zijlstra <peterz@infradead.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@gmail.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@gmail.com> Suggested-by: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Juri Lelli <juri.lelli@gmail.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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