Time stamps for the ring buffer are created by the difference between
two events. Each page of the ring buffer holds a full 64 bit timestamp.
Each event has a 27 bit delta stamp from the last event. The unit of time
is nanoseconds, so 27 bits can hold ~134 milliseconds. If two events
happen more than 134 milliseconds apart, a time extend is inserted
to add more bits for the delta. The time extend has 59 bits, which
is good for ~18 years.
Currently the time extend is committed separately from the event.
If an event is discarded before it is committed, due to filtering,
the time extend still exists. If all events are being filtered, then
after ~134 milliseconds a new time extend will be added to the buffer.
This can only happen till the end of the page. Since each page holds
a full timestamp, there is no reason to add a time extend to the
beginning of a page. Time extends can only fill a page that has actual
data at the beginning, so there is no fear that time extends will fill
more than a page without any data.
When reading an event, a loop is made to skip over time extends
since they are only used to maintain the time stamp and are never
given to the caller. As a paranoid check to prevent the loop running
forever, with the knowledge that time extends may only fill a page,
a check is made that tests the iteration of the loop, and if the
iteration is more than the number of time extends that can fit in a page
a warning is printed and the ring buffer is disabled (all of ftrace
is also disabled with it).
There is another event type that is called a TIMESTAMP which can
hold 64 bits of data in the theoretical case that two events happen
18 years apart. This code has not been implemented, but the name
of this event exists, as well as the structure for it. The
size of a TIMESTAMP is 16 bytes, where as a time extend is only
8 bytes. The macro used to calculate how many time extends can fit on
a page used the TIMESTAMP size instead of the time extend size
cutting the amount in half.
The following test case can easily trigger the warning since we only
need to have half the page filled with time extends to trigger the
warning:
# cd /sys/kernel/debug/tracing/
# echo function > current_tracer
# echo 'common_pid < 0' > events/ftrace/function/filter
# echo > trace
# echo 1 > trace_marker
# sleep 120
# cat trace
Enabling the function tracer and then setting the filter to only trace
functions where the process id is negative (no events), then clearing
the trace buffer to ensure that we have nothing in the buffer,
then write to trace_marker to add an event to the beginning of a page,
sleep for 2 minutes (only 35 seconds is probably needed, but this
guarantees the bug), and then finally reading the trace which will
trigger the bug.
This patch fixes the typo and prevents the false positive of that warning.
Reported-by: Hans J. Koch <hjk@linutronix.de>
Tested-by: Hans J. Koch <hjk@linutronix.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Stable Kernel <stable@kernel.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
* 'rc-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/mmarek/kbuild-2.6:
kbuild: fix oldnoconfig to do the right thing
kconfig: Temporarily disable dependency warnings
kconfig: delay symbol direct dependency initialization
* 'for_linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mjg59/platform-drivers-x86:
IPS driver: Fix limit clamping when reducing CPU power
[PATCH 2/2] IPS driver: disable CPU turbo
IPS driver: apply BIOS provided CPU limit if different from default
intel_ips -- ensure we do not enable gpu turbo mode without driver linkage
intel_ips: Print MCP limit exceeded values.
IPS driver: verify BIOS provided limits
IPS driver: don't toggle CPU turbo on unsupported CPUs
NULL pointer might be used in ips_monitor()
Release symbol on error-handling path of ips_get_i915_syms()
old_cpu_power is wrongly divided by 65535 in ips_monitor()
seqno mask of THM_ITV register is 16bit
We shouldn't return directly here because we're still holding the
&soundcard_mutex.
This bug goes all the way back to the start of git. It's strange that
no one has complained about it as a runtime bug.
CC: stable@kernel.org
Signed-off-by: Dan Carpenter <error27@gmail.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Currently the pressure range in Cintiq 21UX2 is limited to half of the
supported. This patch fixes the problem.
Signed-off-by: Aristeu Rozanski <aris@redhat.com>
Acked-by: Ping Cheng <pingc@wacom.com>
CC: stable@kernel.org
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>
Commit 861b4ea4 broke oldnoconfig when removed the oldnoconfig checks on
if (input_mode == nonint_oldconfig ||
input_mode == oldnoconfig) {
if (input_mode == nonint_oldconfig &&
sym->name &&
!sym_is_choice_value(sym)) {
to avoid oldnoconfig chugging through the else stanza.
Fix that to restore expected behaviour (which I've confirmed in the
Fedora kernel build that the configs end up looking the same.)
Signed-off-by: Kyle McMartin <kyle@redhat.com>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Michal Marek <mmarek@suse.cz>
After fixing a use-after-free bug in kconfig, a 'make defconfig' or
'make allmodconfig' fills the screen with warnings that were not
detected before. Given that we are close to the release now, disable the
warnings temporarily and deal with them after 2.6.36.
Signed-off-by: Michal Marek <mmarek@suse.cz>
* 'release' of git://git.kernel.org/pub/scm/linux/kernel/git/lenb/linux-acpi-2.6:
ACPI: add DMI to disable AML Vista compatibility on MSI GX723 Notebook
ACPI: Handle ACPI0007 Device in acpi_early_set_pdc
* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/sage/ceph-client:
ceph: update issue_seq on cap grant
ceph: send cap release message early on failed revoke.
ceph: Update max_len with minimum required size
ceph: Fix return value of encode_fh function
ceph: avoid null deref in osd request error path
ceph: fix list_add usage on unsafe_writes list
* 'drm-intel-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/ickle/drm-intel:
drm/i915: Prevent module unload to avoid random memory corruption
* 's5p-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/kgene/linux-samsung:
ARM: SAMSUNG: Add a workaround for get_clock() for serial driver
ARM: S5P: Bug fix on errors of build with CONFIG_PREEMPT_NONE
ARM: SAMSUNG: Fix build warnings because of unused codes
Steven Rostedt
Deng-Cheng Zhu
John Blackwood
Linus Torvalds
Takashi Iwai
Luke Yelavich
Dan Carpenter
Aristeu Rozanski
Kyle McMartin
Michal Marek
Andi Kleen
Mike Snitzer
Len Brown