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Subject[PATCH 0/5] Function tracing support for pstore
Hi all,

With this support kernel can save functions call chain log into a
persistent ram buffer that can be decoded and dumped after reboot
through pstore filesystem. It can be used to determine what function
was last called before a hang or an unexpected reset (caused by, for
example, a buggy driver that abuses HW).

Here's a "nano howto", to get the idea:

# mount -t debugfs debugfs /sys/kernel/debug/
# cd /sys/kernel/debug/tracing
# echo persistent > current_tracer
# reboot -f
[...]
# mount -t pstore pstore /mnt/
# tail /mnt/ftrace-ramoops
0 ffffffff8101ea64 ffffffff8101bcda native_apic_mem_read <- disconnect_bsp_APIC+0x6a/0xc0
0 ffffffff8101ea44 ffffffff8101bcf6 native_apic_mem_write <- disconnect_bsp_APIC+0x86/0xc0
0 ffffffff81020084 ffffffff8101a4b5 hpet_disable <- native_machine_shutdown+0x75/0x90
0 ffffffff81005f94 ffffffff8101a4bb iommu_shutdown_noop <- native_machine_shutdown+0x7b/0x90
0 ffffffff8101a6a1 ffffffff8101a437 native_machine_emergency_restart <- native_machine_restart+0x37/0x40
0 ffffffff811f9876 ffffffff8101a73a acpi_reboot <- native_machine_emergency_restart+0xaa/0x1e0
0 ffffffff8101a514 ffffffff8101a772 mach_reboot_fixups <- native_machine_emergency_restart+0xe2/0x1e0
0 ffffffff811d9c54 ffffffff8101a7a0 __const_udelay <- native_machine_emergency_restart+0x110/0x1e0
0 ffffffff811d9c34 ffffffff811d9c80 __delay <- __const_udelay+0x30/0x40
0 ffffffff811d9d14 ffffffff811d9c3f delay_tsc <- __delay+0xf/0x20

Mostly the code comes from trace_persistent.c driver found in the
Android git tree, written by Colin Cross <ccross@android.com>
(according to sign-off history). I reworked the driver a little bit,
and ported it to pstore subsystem.

The patches depend on a pile of other pstore-related work, so
if anyone is willing to try the patches, they would rather grab
the whole git tree:
git://git.infradead.org/users/cbou/linux-pstore.git
or gitweb:
http://git.infradead.org/users/cbou/linux-pstore.git


Note that so far I've tried to not change the original idea, but if
we consider inclusion, there are some open questions:

1. Should we merge persistent tracer with normal function tracer,
i.e. add some flag that makes function tracer to duplicate the
events into pstore (via a callback to pstore)?

2. If we keep the two separate, should the code live in fs/pstore
or kernel/trace?.. I can see valid points for both approaches.

Thanks,

---
Documentation/ramoops.txt | 24 +++++++++
fs/pstore/Kconfig | 12 +++++
fs/pstore/Makefile | 6 +++
fs/pstore/ftrace.c | 122 ++++++++++++++++++++++++++++++++++++++++++++
fs/pstore/inode.c | 111 ++++++++++++++++++++++++++++++++++++++--
fs/pstore/internal.h | 49 ++++++++++++++++++
fs/pstore/platform.c | 13 ++++-
fs/pstore/ram.c | 54 +++++++++++++++-----
include/linux/pstore.h | 5 ++
include/linux/pstore_ram.h | 1 +
kernel/trace/trace.c | 7 +--
11 files changed, 384 insertions(+), 20 deletions(-)

--
Anton Vorontsov
Email: cbouatmailru@gmail.com


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