Messages in this thread Patch in this message | | | Date | Thu, 22 May 2014 05:25:28 -0700 | From | tip-bot for Juri Lelli <> | Subject | [tip:sched/core] sched/deadline: Restrict user params max value to 2^63 ns |
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Commit-ID: b0827819b0da4acfbc1df1e05edcf50efd07cbd1 Gitweb: http://git.kernel.org/tip/b0827819b0da4acfbc1df1e05edcf50efd07cbd1 Author: Juri Lelli <juri.lelli@gmail.com> AuthorDate: Tue, 13 May 2014 14:11:31 +0200 Committer: Ingo Molnar <mingo@kernel.org> CommitDate: Thu, 22 May 2014 10:21:27 +0200
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> 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> --- 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 f3f08bf..44e00ab 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -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; } /*
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