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  1. 17 Mar, 2009 1 commit
    • Guillaume Knispel's avatar
      printk: correct the behavior of printk_timed_ratelimit() · f2d28a2e
      Guillaume Knispel authored 
      
Impact: fix jiffies-comparison sign-wrap behavior

The behavior provided by printk_timed_ratelimit() is, in some
situations, probably not what a caller would reasonably expect:

bool printk_timed_ratelimit(unsigned long *caller_jiffies,
			unsigned int interval_msecs)
{
	if (*caller_jiffies == 0 || time_after(jiffies, *caller_jiffies)) {
		*caller_jiffies = jiffies + msecs_to_jiffies(interval_msecs);
		return true;
	}
	return false;
}

On a 32 bit computer, if printk_timed_ratelimit() is initially called at
time jiffies == Ja, *caller_jiffies is set to
Ja + msecs_to_jiffies(interval_msecs): let's say Ja + 42 for this
example.

If this caller then doesn't call printk_timed_ratelimit() until
jiffies == Ja + (1 << 31) + 42 (which can happen as soon as ~ 25 days
later on a 1000 HZ system), printk_timed_ratelimit() will then always
return false to this caller until jiffies loops completely (1 << 31 more
ticks).

Ths change makes it only return false if jiffies is in the small
time window starting at the previous call when true was returned and
ending interval_msecs later.  Note that if jiffies loops completely
between two calls to printk_timed_ratelimit(), it will obviously still
wrongly return false, but this is something with a low probability.

If something completely reliable is needed I guess jiffies_64 must be
used (which this change does not do).
Signed-off-by: default avatarGuillaume Knispel <gknispel@proformatique.com>
Cc: Ulrich Drepper <drepper@redhat.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Andrew Morton <akpm@osdl.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
LKML-Reference: <20090317161842.0059096b@xilun.lan.proformatique.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
      f2d28a2e
  3. 21 Feb, 2009 1 commit
    • Arve Hjønnevåg's avatar
      PM: Fix suspend_console and resume_console to use only one semaphore · 403f3075
      Arve Hjønnevåg authored 
      
This fixes a race where a thread acquires the console while the
console is suspended, and the console is resumed before this
thread releases it. In this case, the secondary console
semaphore would be left locked, and the primary semaphore would
be released twice. This in turn would cause the console switch
on suspend or resume to hang forever.

Note that suspend_console does not actually lock the console
for clients that use acquire_console_sem, it only locks it for
clients that use try_acquire_console_sem. If we change
suspend_console to fully lock the console, then the kernel
may deadlock on suspend. One client of try_acquire_console_sem
is acquire_console_semaphore_for_printk, which uses it to
prevent printk from using the console while it is suspended.
Signed-off-by: default avatarArve Hjønnevåg <arve@android.com>
Signed-off-by: default avatarRafael J. Wysocki <rjw@sisk.pl>
Cc: Len Brown <lenb@kernel.org>
Cc: Greg KH <gregkh@suse.de>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      403f3075
  5. 14 Jan, 2009 2 commits
  7. 06 Jan, 2009 1 commit
  9. 19 Dec, 2008 1 commit
  11. 23 Oct, 2008 1 commit
  13. 16 Oct, 2008 3 commits
  15. 13 Oct, 2008 1 commit
  17. 20 Aug, 2008 2 commits
    • Jiri Kosina's avatar
      printk: robustify printk, update comment · 1fa63a81
      Jiri Kosina authored 
      
Remove the comment describing the possibility of printk() deadlocking on
runqueue lock.
Signed-off-by: default avatarJiri Kosina <jkosina@suse.cz>
Acked-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
      1fa63a81
    • Peter Zijlstra's avatar
      printk: robustify printk, fix #2 · fa33507a
      Peter Zijlstra authored 
      Dmitry Adamushko reported:

> [*] btw., with DEBUG being enabled, pr_debug() generates [1] when
> debug_smp_processor_id() is used (CONFIG_DEBUG_PREEMPT).
>
> the problem seems to be caused by the following commit:
> commit b845b517


> Author: Peter Zijlstra <a.p.zijlstra@chello.nl>
> Date:   Fri Aug 8 21:47:09 2008 +0200
>
>     printk: robustify printk
>
>
> wake_up_klogd() -> __get_cpu_var() -> smp_processor_id()
>
> and that's being called from release_console_sem() which is, in turn,
> said to be "may be called from any context" [2]
>
> and in this case, it seems to be called from some non-preemptible
> context (although, it can't be printk()...
> although, I haven't looked carefully yet).
>
> Provided [2], __get_cpu_var() is perhaps not the right solution there.
>
>
> [1]
>
> [ 7697.942005] BUG: using smp_processor_id() in preemptible [00000000] code: syslogd/3542
> [ 7697.942005] caller is wake_up_klogd+0x1b/0x50
> [ 7697.942005] Pid: 3542, comm: syslogd Not tainted 2.6.27-rc3-tip-git #2
> [ 7697.942005] Call Trace:
> [ 7697.942005]  [<ffffffff8036b398>] debug_smp_processor_id+0xe8/0xf0
> [ 7697.942005]  [<ffffffff80239d3b>] wake_up_klogd+0x1b/0x50
> [ 7697.942005]  [<ffffffff8023a047>] release_console_sem+0x1e7/0x200
> [ 7697.942005]  [<ffffffff803c0f17>] do_con_write+0xb7/0x1f30
> [ 7697.942005]  [<ffffffff8020d920>] ? show_trace+0x10/0x20
> [ 7697.942005]  [<ffffffff8020dc42>] ? dump_stack+0x72/0x80
> [ 7697.942005]  [<ffffffff8036392d>] ? __ratelimit+0xbd/0xe0
> [ 7697.942005]  [<ffffffff8036b398>] ? debug_smp_processor_id+0xe8/0xf0
> [ 7697.942005]  [<ffffffff80239d3b>] ? wake_up_klogd+0x1b/0x50
> [ 7697.942005]  [<ffffffff8023a047>] ? release_console_sem+0x1e7/0x200
> [ 7697.942005]  [<ffffffff803c2de9>] con_write+0x19/0x30
> [ 7697.942005]  [<ffffffff803b37b6>] write_chan+0x276/0x3c0
> [ 7697.942005]  [<ffffffff80232b20>] ? default_wake_function+0x0/0x10
> [ 7697.942005]  [<ffffffff804cb872>] ? _spin_lock_irqsave+0x22/0x50
> [ 7697.942005]  [<ffffffff803b1334>] tty_write+0x194/0x260
> [ 7697.942005]  [<ffffffff803b3540>] ? write_chan+0x0/0x3c0
> [ 7697.942005]  [<ffffffff803b14a4>] redirected_tty_write+0xa4/0xb0
> [ 7697.942005]  [<ffffffff803b1400>] ? redirected_tty_write+0x0/0xb0
> [ 7697.942005]  [<ffffffff802a88c2>] do_loop_readv_writev+0x52/0x80
> [ 7697.942005]  [<ffffffff802a939d>] do_readv_writev+0x1bd/0x1d0
> [ 7697.942005]  [<ffffffff802a93e9>] vfs_writev+0x39/0x60
> [ 7697.942005]  [<ffffffff802a9870>] sys_writev+0x50/0x90
> [ 7697.942005]  [<ffffffff8020bb3b>] system_call_fastpath+0x16/0x1b
Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
Reported-by: default avatarDmitry Adamushko <dmitry.adamushko@gmail.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
      fa33507a
  19. 11 Aug, 2008 1 commit
  21. 30 Jul, 2008 1 commit
  23. 25 Jul, 2008 1 commit
    • Dave Young's avatar
      printk ratelimiting rewrite · 717115e1
      Dave Young authored 
      
All ratelimit user use same jiffies and burst params, so some messages
(callbacks) will be lost.

For example:
a call printk_ratelimit(5 * HZ, 1)
b call printk_ratelimit(5 * HZ, 1) before the 5*HZ timeout of a, then b will
will be supressed.

- rewrite __ratelimit, and use a ratelimit_state as parameter.  Thanks for
  hints from andrew.

- Add WARN_ON_RATELIMIT, update rcupreempt.h

- remove __printk_ratelimit

- use __ratelimit in net_ratelimit
Signed-off-by: default avatarDave Young <hidave.darkstar@gmail.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: "Paul E. McKenney" <paulmck@us.ibm.com>
Cc: Dave Young <hidave.darkstar@gmail.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      717115e1
  25. 24 Jul, 2008 1 commit
  27. 09 Jul, 2008 1 commit
  29. 08 Jul, 2008 1 commit
  31. 18 Jun, 2008 1 commit
  33. 16 Jun, 2008 1 commit
  35. 27 May, 2008 1 commit
    • Markus Armbruster's avatar
      xen: Enable console tty by default in domU if it's not a dummy · 9e124fe1
      Markus Armbruster authored 
      Without console= arguments on the kernel command line, the first
console to register becomes enabled and the preferred console (the one
behind /dev/console).  This is normally tty (assuming
CONFIG_VT_CONSOLE is enabled, which it commonly is).

This is okay as long tty is a useful console.  But unless we have the
PV framebuffer, and it is enabled for this domain, tty0 in domU is
merely a dummy.  In that case, we want the preferred console to be the
Xen console hvc0, and we want it without having to fiddle with the
kernel command line.  Commit b8c2d3df


did that for us.

Since we now have the PV framebuffer, we want to enable and prefer tty
again, but only when PVFB is enabled.  But even then we still want to
enable the Xen console as well.

Problem: when tty registers, we can't yet know whether the PVFB is
enabled.  By the time we can know (xenstore is up), the console setup
game is over.

Solution: enable console tty by default, but keep hvc as the preferred
console.  Change the preferred console to tty when PVFB probes
successfully, unless we've been given console kernel parameters.
Signed-off-by: default avatarMarkus Armbruster <armbru@redhat.com>
Signed-off-by: default avatarJeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
      9e124fe1
  37. 24 May, 2008 6 commits
  39. 23 May, 2008 1 commit
    • Steven Rostedt's avatar
      ftrace: trace irq disabled critical timings · 81d68a96
      Steven Rostedt authored 
      
This patch adds latency tracing for critical timings
(how long interrupts are disabled for).

 "irqsoff" is added to /debugfs/tracing/available_tracers

Note:
  tracing_max_latency
    also holds the max latency for irqsoff (in usecs).
   (default to large number so one must start latency tracing)

  tracing_thresh
    threshold (in usecs) to always print out if irqs off
    is detected to be longer than stated here.
    If irq_thresh is non-zero, then max_irq_latency
    is ignored.

Here's an example of a trace with ftrace_enabled = 0

=======
preemption latency trace v1.1.5 on 2.6.24-rc7
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
--------------------------------------------------------------------
 latency: 100 us, #3/3, CPU#1 | (M:rt VP:0, KP:0, SP:0 HP:0 #P:2)
    -----------------
    | task: swapper-0 (uid:0 nice:0 policy:0 rt_prio:0)
    -----------------
 => started at: _spin_lock_irqsave+0x2a/0xb7
 => ended at:   _spin_unlock_irqrestore+0x32/0x5f

                 _------=> CPU#
                / _-----=> irqs-off
               | / _----=> need-resched
               || / _---=> hardirq/softirq
               ||| / _--=> preempt-depth
               |||| /
               |||||     delay
   cmd     pid ||||| time  |   caller
      \   /    |||||   \   |   /
 swapper-0     1d.s3    0us+: _spin_lock_irqsave+0x2a/0xb7 (e1000_update_stats+0x47/0x64c [e1000])
 swapper-0     1d.s3  100us : _spin_unlock_irqrestore+0x32/0x5f (e1000_update_stats+0x641/0x64c [e1000])
 swapper-0     1d.s3  100us : trace_hardirqs_on_caller+0x75/0x89 (_spin_unlock_irqrestore+0x32/0x5f)

vim:ft=help
=======

And this is a trace with ftrace_enabled == 1

=======
preemption latency trace v1.1.5 on 2.6.24-rc7
--------------------------------------------------------------------
 latency: 102 us, #12/12, CPU#1 | (M:rt VP:0, KP:0, SP:0 HP:0 #P:2)
    -----------------
    | task: swapper-0 (uid:0 nice:0 policy:0 rt_prio:0)
    -----------------
 => started at: _spin_lock_irqsave+0x2a/0xb7
 => ended at:   _spin_unlock_irqrestore+0x32/0x5f

                 _------=> CPU#
                / _-----=> irqs-off
               | / _----=> need-resched
               || / _---=> hardirq/softirq
               ||| / _--=> preempt-depth
               |||| /
               |||||     delay
   cmd     pid ||||| time  |   caller
      \   /    |||||   \   |   /
 swapper-0     1dNs3    0us+: _spin_lock_irqsave+0x2a/0xb7 (e1000_update_stats+0x47/0x64c [e1000])
 swapper-0     1dNs3   46us : e1000_read_phy_reg+0x16/0x225 [e1000] (e1000_update_stats+0x5e2/0x64c [e1000])
 swapper-0     1dNs3   46us : e1000_swfw_sync_acquire+0x10/0x99 [e1000] (e1000_read_phy_reg+0x49/0x225 [e1000])
 swapper-0     1dNs3   46us : e1000_get_hw_eeprom_semaphore+0x12/0xa6 [e1000] (e1000_swfw_sync_acquire+0x36/0x99 [e1000])
 swapper-0     1dNs3   47us : __const_udelay+0x9/0x47 (e1000_read_phy_reg+0x116/0x225 [e1000])
 swapper-0     1dNs3   47us+: __delay+0x9/0x50 (__const_udelay+0x45/0x47)
 swapper-0     1dNs3   97us : preempt_schedule+0xc/0x84 (__delay+0x4e/0x50)
 swapper-0     1dNs3   98us : e1000_swfw_sync_release+0xc/0x55 [e1000] (e1000_read_phy_reg+0x211/0x225 [e1000])
 swapper-0     1dNs3   99us+: e1000_put_hw_eeprom_semaphore+0x9/0x35 [e1000] (e1000_swfw_sync_release+0x50/0x55 [e1000])
 swapper-0     1dNs3  101us : _spin_unlock_irqrestore+0xe/0x5f (e1000_update_stats+0x641/0x64c [e1000])
 swapper-0     1dNs3  102us : _spin_unlock_irqrestore+0x32/0x5f (e1000_update_stats+0x641/0x64c [e1000])
 swapper-0     1dNs3  102us : trace_hardirqs_on_caller+0x75/0x89 (_spin_unlock_irqrestore+0x32/0x5f)

vim:ft=help
=======
Signed-off-by: default avatarSteven Rostedt <srostedt@redhat.com>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
      81d68a96
  41. 30 Apr, 2008 3 commits
  43. 29 Apr, 2008 1 commit
  45. 15 Apr, 2008 1 commit
  47. 25 Mar, 2008 1 commit
  49. 26 Feb, 2008 1 commit
  51. 08 Feb, 2008 3 commits
  53. 06 Feb, 2008 1 commit