posix-cpu-timers: Provide array based access to expiry cache

Using struct task_cputime for the expiry cache is a pretty odd choice and
comes with magic defines to rename the fields for usage in the expiry
cache.

struct task_cputime is basically a u64 array with 3 members, but it has
distinct members.

The expiry cache content is different than the content of task_cputime
because

  expiry[PROF]  = task_cputime.stime + task_cputime.utime
  expiry[VIRT]  = task_cputime.utime
  expiry[SCHED] = task_cputime.sum_exec_runtime

So there is no direct mapping between task_cputime and the expiry cache and
the #define based remapping is just a horrible hack.

Having the expiry cache array based allows further simplification of the
expiry code.

To avoid an all in one cleanup which is hard to review add a temporary
anonymous union into struct task_cputime which allows array based access to
it. That requires to reorder the members. Add a build time sanity check to
validate that the members are at the same place.

The union and the build time checks will be removed after conversion.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Link: https://lkml.kernel.org/r/20190821192921.105793824@linutronix.de

1 files changed, 11 insertions, 1 deletions

diff --git a/kernel/time/posix-cpu-timers.c b/kernel/time/posix-cpu-timers.c
index 3e29d1692437..a38b6d04e8b5 100644
--- a/kernel/time/posix-cpu-timers.c
+++ b/kernel/time/posix-cpu-timers.c
@@ -18,13 +18,23 @@
 
 #include "posix-timers.h"
 
+static inline void temporary_check(void)
+{
+	BUILD_BUG_ON(offsetof(struct task_cputime, stime) !=
+		     CPUCLOCK_PROF * sizeof(u64));
+	BUILD_BUG_ON(offsetof(struct task_cputime, utime) !=
+		     CPUCLOCK_VIRT * sizeof(u64));
+	BUILD_BUG_ON(offsetof(struct task_cputime, sum_exec_runtime) !=
+		     CPUCLOCK_SCHED * sizeof(u64));
+}
+
 static void posix_cpu_timer_rearm(struct k_itimer *timer);
 
 void posix_cputimers_group_init(struct posix_cputimers *pct, u64 cpu_limit)
 {
 	posix_cputimers_init(pct);
 	if (cpu_limit != RLIM_INFINITY)
-		pct->cputime_expires.prof_exp = cpu_limit * NSEC_PER_SEC;
+		pct->expiries[CPUCLOCK_PROF] = cpu_limit * NSEC_PER_SEC;
 }
 
 /*