Merge tag 'timers-core-2024-11-18' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull timer updates from Thomas Gleixner:
 "A rather large update for timekeeping and timers:

   - The final step to get rid of auto-rearming posix-timers

     posix-timers are currently auto-rearmed by the kernel when the
     signal of the timer is ignored so that the timer signal can be
     delivered once the corresponding signal is unignored.

     This requires to throttle the timer to prevent a DoS by small
     intervals and keeps the system pointlessly out of low power states
     for no value. This is a long standing non-trivial problem due to
     the lock order of posix-timer lock and the sighand lock along with
     life time issues as the timer and the sigqueue have different life
     time rules.

     Cure this by:

       - Embedding the sigqueue into the timer struct to have the same
         life time rules. Aside of that this also avoids the lookup of
         the timer in the signal delivery and rearm path as it's just a
         always valid container_of() now.

       - Queuing ignored timer signals onto a seperate ignored list.

       - Moving queued timer signals onto the ignored list when the
         signal is switched to SIG_IGN before it could be delivered.

       - Walking the ignored list when SIG_IGN is lifted and requeue the
         signals to the actual signal lists. This allows the signal
         delivery code to rearm the timer.

     This also required to consolidate the signal delivery rules so they
     are consistent across all situations. With that all self test
     scenarios finally succeed.

   - Core infrastructure for VFS multigrain timestamping

     This is required to allow the kernel to use coarse grained time
     stamps by default and switch to fine grained time stamps when inode
     attributes are actively observed via getattr().

     These changes have been provided to the VFS tree as well, so that
     the VFS specific infrastructure could be built on top.

   - Cleanup and consolidation of the sleep() infrastructure

       - Move all sleep and timeout functions into one file

       - Rework udelay() and ndelay() into proper documented inline
         functions and replace the hardcoded magic numbers by proper
         defines.

       - Rework the fsleep() implementation to take the reality of the
         timer wheel granularity on different HZ values into account.
         Right now the boundaries are hard coded time ranges which fail
         to provide the requested accuracy on different HZ settings.

       - Update documentation for all sleep/timeout related functions
         and fix up stale documentation links all over the place

       - Fixup a few usage sites

   - Rework of timekeeping and adjtimex(2) to prepare for multiple PTP
     clocks

     A system can have multiple PTP clocks which are participating in
     seperate and independent PTP clock domains. So far the kernel only
     considers the PTP clock which is based on CLOCK TAI relevant as
     that's the clock which drives the timekeeping adjustments via the
     various user space daemons through adjtimex(2).

     The non TAI based clock domains are accessible via the file
     descriptor based posix clocks, but their usability is very limited.
     They can't be accessed fast as they always go all the way out to
     the hardware and they cannot be utilized in the kernel itself.

     As Time Sensitive Networking (TSN) gains traction it is required to
     provide fast user and kernel space access to these clocks.

     The approach taken is to utilize the timekeeping and adjtimex(2)
     infrastructure to provide this access in a similar way how the
     kernel provides access to clock MONOTONIC, REALTIME etc.

     Instead of creating a duplicated infrastructure this rework
     converts timekeeping and adjtimex(2) into generic functionality
     which operates on pointers to data structures instead of using
     static variables.

     This allows to provide time accessors and adjtimex(2) functionality
     for the independent PTP clocks in a subsequent step.

   - Consolidate hrtimer initialization

     hrtimers are set up by initializing the data structure and then
     seperately setting the callback function for historical reasons.

     That's an extra unnecessary step and makes Rust support less
     straight forward than it should be.

     Provide a new set of hrtimer_setup*() functions and convert the
     core code and a few usage sites of the less frequently used
     interfaces over.

     The bulk of the htimer_init() to hrtimer_setup() conversion is
     already prepared and scheduled for the next merge window.

   - Drivers:

       - Ensure that the global timekeeping clocksource is utilizing the
         cluster 0 timer on MIPS multi-cluster systems.

         Otherwise CPUs on different clusters use their cluster specific
         clocksource which is not guaranteed to be synchronized with
         other clusters.

       - Mostly boring cleanups, fixes, improvements and code movement"

* tag 'timers-core-2024-11-18' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (140 commits)
  posix-timers: Fix spurious warning on double enqueue versus do_exit()
  clocksource/drivers/arm_arch_timer: Use of_property_present() for non-boolean properties
  clocksource/drivers/gpx: Remove redundant casts
  clocksource/drivers/timer-ti-dm: Fix child node refcount handling
  dt-bindings: timer: actions,owl-timer: convert to YAML
  clocksource/drivers/ralink: Add Ralink System Tick Counter driver
  clocksource/drivers/mips-gic-timer: Always use cluster 0 counter as clocksource
  clocksource/drivers/timer-ti-dm: Don't fail probe if int not found
  clocksource/drivers:sp804: Make user selectable
  clocksource/drivers/dw_apb: Remove unused dw_apb_clockevent functions
  hrtimers: Delete hrtimer_init_on_stack()
  alarmtimer: Switch to use hrtimer_setup() and hrtimer_setup_on_stack()
  io_uring: Switch to use hrtimer_setup_on_stack()
  sched/idle: Switch to use hrtimer_setup_on_stack()
  hrtimers: Delete hrtimer_init_sleeper_on_stack()
  wait: Switch to use hrtimer_setup_sleeper_on_stack()
  timers: Switch to use hrtimer_setup_sleeper_on_stack()
  net: pktgen: Switch to use hrtimer_setup_sleeper_on_stack()
  futex: Switch to use hrtimer_setup_sleeper_on_stack()
  fs/aio: Switch to use hrtimer_setup_sleeper_on_stack()
  ...

1 files changed, 62 insertions, 17 deletions

diff --git a/include/linux/delay.h b/include/linux/delay.h
index ff9cda975e30..89866bab100d 100644
--- a/include/linux/delay.h
+++ b/include/linux/delay.h
@@ -6,21 +6,12 @@
  * Copyright (C) 1993 Linus Torvalds
  *
  * Delay routines, using a pre-computed "loops_per_jiffy" value.
- *
- * Please note that ndelay(), udelay() and mdelay() may return early for
- * several reasons:
- *  1. computed loops_per_jiffy too low (due to the time taken to
- *     execute the timer interrupt.)
- *  2. cache behaviour affecting the time it takes to execute the
- *     loop function.
- *  3. CPU clock rate changes.
- *
- * Please see this thread:
- *   https://lists.openwall.net/linux-kernel/2011/01/09/56
+ * Sleep routines using timer list timers or hrtimers.
  */
 
 #include <linux/math.h>
 #include <linux/sched.h>
+#include <linux/jiffies.h>
 
 extern unsigned long loops_per_jiffy;
 
@@ -35,12 +26,21 @@ extern unsigned long loops_per_jiffy;
  * The 2nd mdelay() definition ensures GCC will optimize away the 
  * while loop for the common cases where n <= MAX_UDELAY_MS  --  Paul G.
  */
-
 #ifndef MAX_UDELAY_MS
 #define MAX_UDELAY_MS	5
 #endif
 
 #ifndef mdelay
+/**
+ * mdelay - Inserting a delay based on milliseconds with busy waiting
+ * @n:	requested delay in milliseconds
+ *
+ * See udelay() for basic information about mdelay() and it's variants.
+ *
+ * Please double check, whether mdelay() is the right way to go or whether a
+ * refactoring of the code is the better variant to be able to use msleep()
+ * instead.
+ */
 #define mdelay(n) (\
 	(__builtin_constant_p(n) && (n)<=MAX_UDELAY_MS) ? udelay((n)*1000) : \
 	({unsigned long __ms=(n); while (__ms--) udelay(1000);}))
@@ -63,30 +63,75 @@ unsigned long msleep_interruptible(unsigned int msecs);
 void usleep_range_state(unsigned long min, unsigned long max,
 			unsigned int state);
 
+/**
+ * usleep_range - Sleep for an approximate time
+ * @min:	Minimum time in microseconds to sleep
+ * @max:	Maximum time in microseconds to sleep
+ *
+ * For basic information please refere to usleep_range_state().
+ *
+ * The task will be in the state TASK_UNINTERRUPTIBLE during the sleep.
+ */
 static inline void usleep_range(unsigned long min, unsigned long max)
 {
 	usleep_range_state(min, max, TASK_UNINTERRUPTIBLE);
 }
 
-static inline void usleep_idle_range(unsigned long min, unsigned long max)
+/**
+ * usleep_range_idle - Sleep for an approximate time with idle time accounting
+ * @min:	Minimum time in microseconds to sleep
+ * @max:	Maximum time in microseconds to sleep
+ *
+ * For basic information please refere to usleep_range_state().
+ *
+ * The sleeping task has the state TASK_IDLE during the sleep to prevent
+ * contribution to the load avarage.
+ */
+static inline void usleep_range_idle(unsigned long min, unsigned long max)
 {
 	usleep_range_state(min, max, TASK_IDLE);
 }
 
+/**
+ * ssleep - wrapper for seconds around msleep
+ * @seconds:	Requested sleep duration in seconds
+ *
+ * Please refere to msleep() for detailed information.
+ */
 static inline void ssleep(unsigned int seconds)
 {
 	msleep(seconds * 1000);
 }
 
-/* see Documentation/timers/timers-howto.rst for the thresholds */
+static const unsigned int max_slack_shift = 2;
+#define USLEEP_RANGE_UPPER_BOUND	((TICK_NSEC << max_slack_shift) / NSEC_PER_USEC)
+
+/**
+ * fsleep - flexible sleep which autoselects the best mechanism
+ * @usecs:	requested sleep duration in microseconds
+ *
+ * flseep() selects the best mechanism that will provide maximum 25% slack
+ * to the requested sleep duration. Therefore it uses:
+ *
+ * * udelay() loop for sleep durations <= 10 microseconds to avoid hrtimer
+ *   overhead for really short sleep durations.
+ * * usleep_range() for sleep durations which would lead with the usage of
+ *   msleep() to a slack larger than 25%. This depends on the granularity of
+ *   jiffies.
+ * * msleep() for all other sleep durations.
+ *
+ * Note: When %CONFIG_HIGH_RES_TIMERS is not set, all sleeps are processed with
+ * the granularity of jiffies and the slack might exceed 25% especially for
+ * short sleep durations.
+ */
 static inline void fsleep(unsigned long usecs)
 {
 	if (usecs <= 10)
 		udelay(usecs);
-	else if (usecs <= 20000)
-		usleep_range(usecs, 2 * usecs);
+	else if (usecs < USLEEP_RANGE_UPPER_BOUND)
+		usleep_range(usecs, usecs + (usecs >> max_slack_shift));
 	else
-		msleep(DIV_ROUND_UP(usecs, 1000));
+		msleep(DIV_ROUND_UP(usecs, USEC_PER_MSEC));
 }
 
 #endif /* defined(_LINUX_DELAY_H) */