linux/fs/proc
Michal Hocko 2a95ea6c0d procfs: do not overflow get_{idle,iowait}_time for nohz
Since commit a25cac5198 ("proc: Consider NO_HZ when printing idle and
iowait times") we are reporting idle/io_wait time also while a CPU is
tickless.  We rely on get_{idle,iowait}_time functions to retrieve
proper data.

These functions, however, use usecs_to_cputime to translate micro
seconds time to cputime64_t.  This is just an alias to usecs_to_jiffies
which reduces the data type from u64 to unsigned int and also checks
whether the given parameter overflows jiffies_to_usecs(MAX_JIFFY_OFFSET)
and returns MAX_JIFFY_OFFSET in that case.

When we overflow depends on CONFIG_HZ but especially for CONFIG_HZ_300
it is quite low (1431649781) so we are getting MAX_JIFFY_OFFSET for
>3000s! until we overflow unsigned int.  Just for reference
CONFIG_HZ_100 has an overflow window around 20s, CONFIG_HZ_250 ~8s and
CONFIG_HZ_1000 ~2s.

This results in a bug when people saw [h]top going mad reporting 100%
CPU usage even though there was basically no CPU load.  The reason was
simply that /proc/stat stopped reporting idle/io_wait changes (and
reported MAX_JIFFY_OFFSET) and so the only change happening was for user
system time.

Let's use nsecs_to_jiffies64 instead which doesn't reduce the precision
to 32b type and it is much more appropriate for cumulative time values
(unlike usecs_to_jiffies which intended for timeout calculations).

Signed-off-by: Michal Hocko <mhocko@suse.cz>
Tested-by: Artem S. Tashkinov <t.artem@mailcity.com>
Cc: Dave Jones <davej@redhat.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2011-12-09 07:50:29 -08:00
..
array.c ptrace: s/tracehook_tracer_task()/ptrace_parent()/ 2011-06-22 19:26:29 +02:00
base.c Revert "proc: fix races against execve() of /proc/PID/fd**" 2011-11-09 18:16:00 -05:00
cmdline.c proc: switch /proc/cmdline to seq_file 2008-10-23 14:29:04 +04:00
consoles.c console: rename acquire/release_console_sem() to console_lock/unlock() 2011-01-26 10:50:06 +10:00
cpuinfo.c proc: move /proc/cpuinfo code to fs/proc/cpuinfo.c 2008-10-23 15:05:11 +04:00
devices.c proc: use seq_puts()/seq_putc() where possible 2011-01-13 08:03:16 -08:00
generic.c filesystems: add set_nlink() 2011-11-02 12:53:43 +01:00
inode.c filesystems: add set_nlink() 2011-11-02 12:53:43 +01:00
internal.h Merge git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/linux-2.6-nsfd 2011-05-25 18:10:16 -07:00
interrupts.c proc: move /proc/interrupts boilerplate code to fs/proc/interrupts.c 2008-10-23 15:15:46 +04:00
Kconfig kconfig: rename CONFIG_EMBEDDED to CONFIG_EXPERT 2011-01-20 17:02:05 -08:00
kcore.c /proc/kcore: fix seeking 2011-01-13 08:03:17 -08:00
kmsg.c procfs: Use generic_file_llseek in /proc/kmsg 2010-04-09 16:35:41 +02:00
loadavg.c sched, timers: cleanup avenrun users 2009-05-15 15:32:45 +02:00
Makefile ns: proc files for namespace naming policy. 2011-05-10 14:31:44 -07:00
meminfo.c fs/proc/meminfo.c: fix compilation error 2011-12-09 07:50:28 -08:00
mmu.c fs/proc/mmu.c: headers butchery 2007-10-17 08:42:48 -07:00
namespaces.c proc: Fix Oops on stat of /proc/<zombie pid>/ns/net 2011-06-15 14:35:29 -07:00
nommu.c include cleanup: Update gfp.h and slab.h includes to prepare for breaking implicit slab.h inclusion from percpu.h 2010-03-30 22:02:32 +09:00
page.c thp: remove PG_buddy 2011-01-13 17:32:43 -08:00
proc_devtree.c of/flattree: Drop an uninteresting message to pr_debug level 2011-03-02 13:45:18 -07:00
proc_net.c proc: make struct proc_dir_entry::name a terminal array rather than a pointer 2011-07-27 12:50:45 -07:00
proc_sysctl.c Merge branch 'akpm' (Andrew's incoming - part two) 2011-11-02 16:07:27 -07:00
proc_tty.c proc: use seq_puts()/seq_putc() where possible 2011-01-13 08:03:16 -08:00
root.c proc: make struct proc_dir_entry::name a terminal array rather than a pointer 2011-07-27 12:50:45 -07:00
softirqs.c proc: use seq_puts()/seq_putc() where possible 2011-01-13 08:03:16 -08:00
stat.c procfs: do not overflow get_{idle,iowait}_time for nohz 2011-12-09 07:50:29 -08:00
task_mmu.c mm: distinguish between mlocked and pinned pages 2011-10-31 17:30:46 -07:00
task_nommu.c report errors in /proc/*/*map* sanely 2011-03-23 16:36:50 -04:00
uptime.c [PATCH] Fix idle time field in /proc/uptime 2009-09-24 10:16:24 +02:00
version.c proc: switch /proc/version to seq_file 2008-10-23 14:19:58 +04:00
vmcore.c fs: add export.h to files using EXPORT_SYMBOL/THIS_MODULE macros 2011-10-31 19:30:31 -04:00