linux-toradex.git/kernel/printk, branch v3.17-rc4

printk: Add function to return log buffer address and size

2014-08-13T05:13:44+00:00

Platforms like IBM Power Systems supports service processor
assisted dump. It provides interface to add memory region to
be captured when system is crashed.

During initialization/running we can add kernel memory region
to be collected.

Presently we don't have a way to get the log buffer base address
and size. This patch adds support to return log buffer address
and size.

Signed-off-by: Vasant Hegde 
Signed-off-by: Benjamin Herrenschmidt 
Acked-by: Andrew Morton

kernel/printk/printk.c: fix bool assignements

2014-08-07T01:01:24+00:00

Fix coccinelle warnings.

Signed-off-by: Neil Zhang 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

printk: enable interrupts before calling console_trylock_for_printk()

2014-08-07T01:01:24+00:00

We need interrupts disabled when calling console_trylock_for_printk()
only so that cpu id we pass to can_use_console() remains valid (for
other things console_sem provides all the exclusion we need and
deadlocks on console_sem due to interrupts are impossible because we use
down_trylock()).  However if we are rescheduled, we are guaranteed to
run on an online cpu so we can easily just get the cpu id in
can_use_console().

We can lose a bit of performance when we enable interrupts in
vprintk_emit() and then disable them again in console_unlock() but OTOH
it can somewhat reduce interrupt latency caused by console_unlock().

We differ from (reverted) commit 939f04bec1a4 in that we avoid calling
console_unlock() from vprintk_emit() with lockdep enabled as that has
unveiled quite some bugs leading to system freezes during boot (e.g.
  https://lkml.org/lkml/2014/5/30/242,
  https://lkml.org/lkml/2014/6/28/521).

Signed-off-by: Jan Kara 
Tested-by: Andreas Bombe 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

printk: miscellaneous cleanups

2014-08-07T01:01:24+00:00

Some small cleanups to kernel/printk/printk.c.  None of them should
cause any change in behavior.

  - When CONFIG_PRINTK is defined, parenthesize the value of LOG_LINE_MAX.
  - When CONFIG_PRINTK is *not* defined, there is an extra LOG_LINE_MAX
    definition; delete it.
  - Pull an assignment out of a conditional expression in console_setup().
  - Use isdigit() in console_setup() rather than open coding it.
  - In update_console_cmdline(), drop a NUL-termination assignment;
    the strlcpy() call that precedes it guarantees it's not needed.
  - Simplify some logic in printk_timed_ratelimit().

Signed-off-by: Alex Elder 
Reviewed-by: Petr Mladek 
Cc: Andi Kleen 
Cc: Borislav Petkov 
Cc: Jan Kara 
Cc: John Stultz 
Cc: Steven Rostedt 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

printk: use a clever macro

2014-08-07T01:01:24+00:00

Use the IS_ENABLED() macro rather than #ifdef blocks to set certain
global values.

Signed-off-by: Alex Elder 
Acked-by: Borislav Petkov 
Reviewed-by: Petr Mladek 
Cc: Andi Kleen 
Cc: Jan Kara 
Cc: John Stultz 
Cc: Steven Rostedt 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

printk: fix some comments

2014-08-07T01:01:24+00:00

Fix a few comments that don't accurately describe their corresponding
code.  It also fixes some minor typographical errors.

Signed-off-by: Alex Elder 
Reviewed-by: Petr Mladek 
Cc: Andi Kleen 
Cc: Borislav Petkov 
Cc: Jan Kara 
Cc: John Stultz 
Cc: Steven Rostedt 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

printk: rename DEFAULT_MESSAGE_LOGLEVEL

2014-08-07T01:01:24+00:00

Commit a8fe19ebfbfd ("kernel/printk: use symbolic defines for console
loglevels") makes consistent use of symbolic values for printk() log
levels.

The naming scheme used is different from the one used for
DEFAULT_MESSAGE_LOGLEVEL though.  Change that symbol name to be
MESSAGE_LOGLEVEL_DEFAULT for consistency.  And because the value of that
symbol comes from a similarly-named config option, rename
CONFIG_DEFAULT_MESSAGE_LOGLEVEL as well.

Signed-off-by: Alex Elder 
Cc: Andi Kleen 
Cc: Borislav Petkov 
Cc: Jan Kara 
Cc: John Stultz 
Cc: Petr Mladek 
Cc: Steven Rostedt 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

printk: tweak do_syslog() to match comments

2014-08-07T01:01:24+00:00

In do_syslog() there's a path used by kmsg_poll() and kmsg_read() that
only needs to know whether there's any data available to read (and not
its size).  These callers only check for non-zero return.  As a
shortcut, do_syslog() returns the difference between what has been
logged and what has been "seen."

The comments say that the "count of records" should be returned but it's
not.  Instead it returns (log_next_idx - syslog_idx), which is a
difference between buffer offsets--and the result could be negative.

The behavior is the same (it'll be zero or not in the same cases), but
the count of records is more meaningful and it matches what the comments
say.  So change the code to return that.

Signed-off-by: Alex Elder 
Cc: Petr Mladek 
Cc: Jan Kara 
Cc: Joe Perches 
Cc: John Stultz 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

printk: allow increasing the ring buffer depending on the number of CPUs

2014-08-07T01:01:23+00:00

The default size of the ring buffer is too small for machines with a
large amount of CPUs under heavy load.  What ends up happening when
debugging is the ring buffer overlaps and chews up old messages making
debugging impossible unless the size is passed as a kernel parameter.
An idle system upon boot up will on average spew out only about one or
two extra lines but where this really matters is on heavy load and that
will vary widely depending on the system and environment.

There are mechanisms to help increase the kernel ring buffer for tracing
through debugfs, and those interfaces even allow growing the kernel ring
buffer per CPU.  We also have a static value which can be passed upon
boot.  Relying on debugfs however is not ideal for production, and
relying on the value passed upon bootup is can only used *after* an
issue has creeped up.  Instead of being reactive this adds a proactive
measure which lets you scale the amount of contributions you'd expect to
the kernel ring buffer under load by each CPU in the worst case
scenario.

We use num_possible_cpus() to avoid complexities which could be
introduced by dynamically changing the ring buffer size at run time,
num_possible_cpus() lets us use the upper limit on possible number of
CPUs therefore avoiding having to deal with hotplugging CPUs on and off.
This introduces the kernel configuration option LOG_CPU_MAX_BUF_SHIFT
which is used to specify the maximum amount of contributions to the
kernel ring buffer in the worst case before the kernel ring buffer flips
over, the size is specified as a power of 2.  The total amount of
contributions made by each CPU must be greater than half of the default
kernel ring buffer size (1 << LOG_BUF_SHIFT bytes) in order to trigger
an increase upon bootup.  The kernel ring buffer is increased to the
next power of two that would fit the required minimum kernel ring buffer
size plus the additional CPU contribution.  For example if LOG_BUF_SHIFT
is 18 (256 KB) you'd require at least 128 KB contributions by other CPUs
in order to trigger an increase of the kernel ring buffer.  With a
LOG_CPU_BUF_SHIFT of 12 (4 KB) you'd require at least anything over > 64
possible CPUs to trigger an increase.  If you had 128 possible CPUs the
amount of minimum required kernel ring buffer bumps to:

   ((1 << 18) + ((128 - 1) * (1 << 12))) / 1024 = 764 KB

Since we require the ring buffer to be a power of two the new required
size would be 1024 KB.

This CPU contributions are ignored when the "log_buf_len" kernel
parameter is used as it forces the exact size of the ring buffer to an
expected power of two value.

[pmladek@suse.cz: fix build]
Signed-off-by: Luis R. Rodriguez 
Signed-off-by: Petr Mladek 
Tested-by: Davidlohr Bueso 
Tested-by: Petr Mladek 
Reviewed-by: Davidlohr Bueso 
Cc: Andrew Lunn 
Cc: Stephen Warren 
Cc: Michal Hocko 
Cc: Petr Mladek 
Cc: Joe Perches 
Cc: Arun KS 
Cc: Kees Cook 
Cc: Davidlohr Bueso 
Cc: Chris Metcalf 
Cc: Jan Kara 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

printk: make dynamic units clear for the kernel ring buffer

2014-08-07T01:01:23+00:00

Signed-off-by: Luis R. Rodriguez 
Suggested-by: Davidlohr Bueso 
Cc: Andrew Lunn 
Cc: Stephen Warren 
Cc: Greg Kroah-Hartman 
Cc: Michal Hocko 
Cc: Petr Mladek 
Cc: Joe Perches 
Cc: Arun KS 
Cc: Kees Cook 
Cc: Davidlohr Bueso 
Cc: Chris Metcalf 
Cc: Jan Kara 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds