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

diff --git a/include/linux/posix-timers.h b/include/linux/posix-timers.h
index a3731ba15bce49f2f0e31514afbdcd00f0f0db74..ed0f6ec30aa65559728c021d4f7235e99186de41 100644 (file)
--- a/include/linux/posix-timers.h
+++ b/include/linux/posix-timers.h
@@ -65,27 +65,39 @@ static inline int clockid_to_fd(const clockid_t clk)
 /*
  * Alternate field names for struct task_cputime when used on cache
  * expirations. Will go away soon.
+ *
+ * stime corresponds to CLOCKCPU_PROF
+ * utime corresponds to CLOCKCPU_VIRT
+ * sum_exex_runtime corresponds to CLOCKCPU_SCHED
+ *
+ * The ordering is currently enforced so struct task_cputime and the
+ * expiries array in struct posix_cputimers are equivalent.
  */
-#define virt_exp                       utime
 #define prof_exp                       stime
+#define virt_exp                       utime
 #define sched_exp                      sum_exec_runtime
 
 #ifdef CONFIG_POSIX_TIMERS
 /**
  * posix_cputimers - Container for posix CPU timer related data
- * @cputime_expires:   Earliest-expiration cache
+ * @cputime_expires:   Earliest-expiration cache task_cputime based
+ * @expiries:          Earliest-expiration cache array based
  * @cpu_timers:                List heads to queue posix CPU timers
  *
  * Used in task_struct and signal_struct
  */
 struct posix_cputimers {
-       struct task_cputime     cputime_expires;
-       struct list_head        cpu_timers[CPUCLOCK_MAX];
+       /* Temporary union until all users are cleaned up */
+       union {
+               struct task_cputime     cputime_expires;
+               u64                     expiries[CPUCLOCK_MAX];
+       };
+       struct list_head                cpu_timers[CPUCLOCK_MAX];
 };
 
 static inline void posix_cputimers_init(struct posix_cputimers *pct)
 {
-       memset(&pct->cputime_expires, 0, sizeof(pct->cputime_expires));
+       memset(&pct->expiries, 0, sizeof(pct->expiries));
        INIT_LIST_HEAD(&pct->cpu_timers[0]);
        INIT_LIST_HEAD(&pct->cpu_timers[1]);
        INIT_LIST_HEAD(&pct->cpu_timers[2]);
@@ -96,7 +108,7 @@ void posix_cputimers_group_init(struct posix_cputimers *pct, u64 cpu_limit);
 static inline void posix_cputimers_rt_watchdog(struct posix_cputimers *pct,
                                               u64 runtime)
 {
-       pct->cputime_expires.sched_exp = runtime;
+       pct->expiries[CPUCLOCK_SCHED] = runtime;
 }
 
 /* Init task static initializer */

diff --git a/include/linux/sched/types.h b/include/linux/sched/types.h
index 2c5c28ddd9b2078f20e1cf1f7db82c453a713428..3c3e049224ae2cf8165d4047b9f51efed6b57ad5 100644 (file)
--- a/include/linux/sched/types.h
+++ b/include/linux/sched/types.h
@@ -6,8 +6,8 @@
 
 /**
  * struct task_cputime - collected CPU time counts
- * @utime:             time spent in user mode, in nanoseconds
  * @stime:             time spent in kernel mode, in nanoseconds
+ * @utime:             time spent in user mode, in nanoseconds
  * @sum_exec_runtime:  total time spent on the CPU, in nanoseconds
  *
  * This structure groups together three kinds of CPU time that are tracked for
@@ -15,8 +15,8 @@
  * these counts together and treat all three of them in parallel.
  */
 struct task_cputime {
-       u64                             utime;
        u64                             stime;
+       u64                             utime;
        unsigned long long              sum_exec_runtime;
 };
 

diff --git a/kernel/time/posix-cpu-timers.c b/kernel/time/posix-cpu-timers.c
index 3e29d169243757898a966d4a4b2b39995148e65e..a38b6d04e8b50f004d5ac62580e1ea888c1d1061 100644 (file)
--- 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;
 }
 
 /*