[PATCH 0/5] Function tracing support for pstore

[PATCH 0/5] Function tracing support for pstore

[Anton Vorontsov]

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

[PATCH 1/5] tracing: Fix initialization failure path in tracing_set_tracer()

[Anton Vorontsov]

If tracer->init() fails, current code will leave current_tracer pointing
to an unusable tracer, which at best makes 'current_tracer' report
inaccurate value.

Fix the issue by pointing current_tracer to nop tracer, and only update
current_tracer with the new one after all the initialization succeeds.

Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org>
---
 kernel/trace/trace.c |    7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 68032c6..5cf7e67 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -3172,10 +3172,10 @@ static int tracing_set_tracer(const char *buf)
 	}
 	destroy_trace_option_files(topts);
 
-	current_trace = t;
+	current_trace = &nop_trace;
 
-	topts = create_trace_option_files(current_trace);
-	if (current_trace->use_max_tr) {
+	topts = create_trace_option_files(t);
+	if (t->use_max_tr) {
 		int cpu;
 		/* we need to make per cpu buffer sizes equivalent */
 		for_each_tracing_cpu(cpu) {
@@ -3195,6 +3195,7 @@ static int tracing_set_tracer(const char *buf)
 			goto out;
 	}
 
+	current_trace = t;
 	trace_branch_enable(tr);
  out:
 	mutex_unlock(&trace_types_lock);
-- 
1.7.9.2

Re: [PATCH 1/5] tracing: Fix initialization failure path in tracing_set_tracer()

[Steven Rostedt]

On Sat, 2012-05-26 at 06:39 -0700, Anton Vorontsov wrote:
> If tracer->init() fails, current code will leave current_tracer pointing
> to an unusable tracer, which at best makes 'current_tracer' report
> inaccurate value.
> 
> Fix the issue by pointing current_tracer to nop tracer, and only update
> current_tracer with the new one after all the initialization succeeds.
> 

Hmm, I'll look at this in more detail. This may be something I pull now.
(for 3.6).

-- Steve

> Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org>
> ---
>  kernel/trace/trace.c |    7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index 68032c6..5cf7e67 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -3172,10 +3172,10 @@ static int tracing_set_tracer(const char *buf)
>  	}
>  	destroy_trace_option_files(topts);
>  
> -	current_trace = t;
> +	current_trace = &nop_trace;
>  
> -	topts = create_trace_option_files(current_trace);
> -	if (current_trace->use_max_tr) {
> +	topts = create_trace_option_files(t);
> +	if (t->use_max_tr) {
>  		int cpu;
>  		/* we need to make per cpu buffer sizes equivalent */
>  		for_each_tracing_cpu(cpu) {
> @@ -3195,6 +3195,7 @@ static int tracing_set_tracer(const char *buf)
>  			goto out;
>  	}
>  
> +	current_trace = t;
>  	trace_branch_enable(tr);
>   out:
>  	mutex_unlock(&trace_types_lock);

[PATCH 2/5] pstore: Introduce write_buf backend callback

[Anton Vorontsov]

For function tracing we need to stop using pstore.buf directly, since
in a tracing callback we can't use spinlocks, and thus we can't safely
use the global buffer.

With write_buf callback, backends no longer need to access pstore.buf
directly, and thus we can pass any buffers (e.g. allocated on stack).

Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org>
---
 fs/pstore/platform.c   |   10 ++++++++++
 include/linux/pstore.h |    4 ++++
 2 files changed, 14 insertions(+)

diff --git a/fs/pstore/platform.c b/fs/pstore/platform.c
index be4614f..e7c0a52 100644
--- a/fs/pstore/platform.c
+++ b/fs/pstore/platform.c
@@ -198,6 +198,14 @@ static void pstore_register_console(void)
 static void pstore_register_console(void) {}
 #endif
 
+static int pstore_write_compat(enum pstore_type_id type,
+			       enum kmsg_dump_reason reason,
+			       u64 *id, unsigned int part,
+			       size_t size, struct pstore_info *psi)
+{
+	return psi->write_buf(type, reason, id, part, psinfo->buf, size, psi);
+}
+
 /*
  * platform specific persistent storage driver registers with
  * us here. If pstore is already mounted, call the platform
@@ -222,6 +230,8 @@ int pstore_register(struct pstore_info *psi)
 		return -EINVAL;
 	}
 
+	if (!psi->write)
+		psi->write = pstore_write_compat;
 	psinfo = psi;
 	mutex_init(&psinfo->read_mutex);
 	spin_unlock(&pstore_lock);
diff --git a/include/linux/pstore.h b/include/linux/pstore.h
index 1bd014b..b107484 100644
--- a/include/linux/pstore.h
+++ b/include/linux/pstore.h
@@ -48,6 +48,10 @@ struct pstore_info {
 	int		(*write)(enum pstore_type_id type,
 			enum kmsg_dump_reason reason, u64 *id,
 			unsigned int part, size_t size, struct pstore_info *psi);
+	int		(*write_buf)(enum pstore_type_id type,
+			enum kmsg_dump_reason reason, u64 *id,
+			unsigned int part, const char *buf, size_t size,
+			struct pstore_info *psi);
 	int		(*erase)(enum pstore_type_id type, u64 id,
 			struct pstore_info *psi);
 	void		*data;
-- 
1.7.9.2

Re: [PATCH 2/5] pstore: Introduce write_buf backend callback

[Kees Cook]

On Sat, May 26, 2012 at 6:39 AM, Anton Vorontsov
<anton.vorontsov@linaro.org> wrote:
> For function tracing we need to stop using pstore.buf directly, since
> in a tracing callback we can't use spinlocks, and thus we can't safely
> use the global buffer.
>
> With write_buf callback, backends no longer need to access pstore.buf
> directly, and thus we can pass any buffers (e.g. allocated on stack).

Hrm, I thought the point of having pstore.buf pre-mapped was to allow
Oopses to be able to write directly to it without needing to hit any
additional kernel code. Maybe I'm misunderstanding this change,
though. I'd like to see Tony's opinion on it.

-Kees

> Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org>
> ---
>  fs/pstore/platform.c   |   10 ++++++++++
>  include/linux/pstore.h |    4 ++++
>  2 files changed, 14 insertions(+)
>
> diff --git a/fs/pstore/platform.c b/fs/pstore/platform.c
> index be4614f..e7c0a52 100644
> --- a/fs/pstore/platform.c
> +++ b/fs/pstore/platform.c
> @@ -198,6 +198,14 @@ static void pstore_register_console(void)
>  static void pstore_register_console(void) {}
>  #endif
>
> +static int pstore_write_compat(enum pstore_type_id type,
> +                              enum kmsg_dump_reason reason,
> +                              u64 *id, unsigned int part,
> +                              size_t size, struct pstore_info *psi)
> +{
> +       return psi->write_buf(type, reason, id, part, psinfo->buf, size, psi);
> +}
> +
>  /*
>  * platform specific persistent storage driver registers with
>  * us here. If pstore is already mounted, call the platform
> @@ -222,6 +230,8 @@ int pstore_register(struct pstore_info *psi)
>                return -EINVAL;
>        }
>
> +       if (!psi->write)
> +               psi->write = pstore_write_compat;
>        psinfo = psi;
>        mutex_init(&psinfo->read_mutex);
>        spin_unlock(&pstore_lock);
> diff --git a/include/linux/pstore.h b/include/linux/pstore.h
> index 1bd014b..b107484 100644
> --- a/include/linux/pstore.h
> +++ b/include/linux/pstore.h
> @@ -48,6 +48,10 @@ struct pstore_info {
>        int             (*write)(enum pstore_type_id type,
>                        enum kmsg_dump_reason reason, u64 *id,
>                        unsigned int part, size_t size, struct pstore_info *psi);
> +       int             (*write_buf)(enum pstore_type_id type,
> +                       enum kmsg_dump_reason reason, u64 *id,
> +                       unsigned int part, const char *buf, size_t size,
> +                       struct pstore_info *psi);
>        int             (*erase)(enum pstore_type_id type, u64 id,
>                        struct pstore_info *psi);
>        void            *data;
> --
> 1.7.9.2
>



-- 
Kees Cook
Chrome OS Security

RE: [PATCH 2/5] pstore: Introduce write_buf backend callback

[Luck, Tony]

> Hrm, I thought the point of having pstore.buf pre-mapped was to allow
> Oopses to be able to write directly to it without needing to hit any
> additional kernel code. Maybe I'm misunderstanding this change,
> though. I'd like to see Tony's opinion on it.

Yes - the ERST backend needs to have a bunch of header ugliness (with
special UUIDs) at the front of the buffer that is stored to non-volatile
storage. So it allocates its own buffer with all that junk, and then
passes the address of the plain data portion of the buffer on to the
pstore layer.

As we add more backends, it might be that this is only applicable to
ERST, and so it might make sense to have it copy the data from some
other buffer into its specially crafted one.  But we should not lose
the "no allocations" property ... everything needed should be pre-allocated
so we don't have to try to allocate any memory during a panic.

-Tony

Re: [PATCH 2/5] pstore: Introduce write_buf backend callback

[Anton Vorontsov]

On Tue, May 29, 2012 at 06:00:16PM +0000, Luck, Tony wrote:
> > Hrm, I thought the point of having pstore.buf pre-mapped was to allow
> > Oopses to be able to write directly to it without needing to hit any
> > additional kernel code. Maybe I'm misunderstanding this change,
> > though. I'd like to see Tony's opinion on it.
> 
> Yes - the ERST backend needs to have a bunch of header ugliness (with
> special UUIDs) at the front of the buffer that is stored to non-volatile
> storage. So it allocates its own buffer with all that junk, and then
> passes the address of the plain data portion of the buffer on to the
> pstore layer.
> 
> As we add more backends, it might be that this is only applicable to
> ERST, and so it might make sense to have it copy the data from some
> other buffer into its specially crafted one.  But we should not lose
> the "no allocations" property ... everything needed should be pre-allocated
> so we don't have to try to allocate any memory during a panic.

Yep, and everything is still pre-allocated.

The only change is that we can pass different buffers, and in tracing
case it is allocated on the stack (we can't use pstore.buf for tracing
as it would require grabbing pstore_lock, which we can't do -- the
locking operations are traced too, so it would recurse).

Thanks,

-- 
Anton Vorontsov
Email: cbouatmailru@gmail.com

[PATCH 3/5] pstore: Add persistent function tracing

[Anton Vorontsov]

With this support kernel can save function 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 reset or panic.

We store the log in a binary format and then decode it at read time.

p.s.
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.

Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org>
---
 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   |    3 +-
 include/linux/pstore.h |    1 +
 7 files changed, 299 insertions(+), 5 deletions(-)
 create mode 100644 fs/pstore/ftrace.c

diff --git a/fs/pstore/Kconfig b/fs/pstore/Kconfig
index d044de6..d39bb5c 100644
--- a/fs/pstore/Kconfig
+++ b/fs/pstore/Kconfig
@@ -19,6 +19,18 @@ config PSTORE_CONSOLE
 	  When the option is enabled, pstore will log all kernel
 	  messages, even if no oops or panic happened.
 
+config PSTORE_FTRACE
+	bool "Persistent function tracer"
+	depends on PSTORE
+	depends on FUNCTION_TRACER
+	help
+	  With this option kernel traces function calls 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 reset or panic.
+
+	  If unsure, say N.
+
 config PSTORE_RAM
 	tristate "Log panic/oops to a RAM buffer"
 	depends on PSTORE
diff --git a/fs/pstore/Makefile b/fs/pstore/Makefile
index 278a44e..cc6aa3d 100644
--- a/fs/pstore/Makefile
+++ b/fs/pstore/Makefile
@@ -7,4 +7,10 @@ obj-y += pstore.o
 pstore-objs += inode.o platform.o
 
 ramoops-objs += ram.o ram_core.o
+
+ifeq ($(CONFIG_PSTORE_FTRACE),y)
+ramoops-objs += ftrace.o
+CFLAGS_REMOVE_ftrace.o = -pg
+endif
+
 obj-$(CONFIG_PSTORE_RAM)	+= ramoops.o
diff --git a/fs/pstore/ftrace.c b/fs/pstore/ftrace.c
new file mode 100644
index 0000000..eb16773
--- /dev/null
+++ b/fs/pstore/ftrace.c
@@ -0,0 +1,122 @@
+/*
+ * Copyright 2012  Google, Inc.
+ *
+ * This software is licensed under the terms of the GNU General Public
+ * License version 2, as published by the Free Software Foundation, and
+ * may be copied, distributed, and modified under those terms.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ */
+
+#include <linux/kernel.h>
+#include <linux/compiler.h>
+#include <linux/irqflags.h>
+#include <linux/smp.h>
+#include <linux/atomic.h>
+#include <asm/barrier.h>
+#include "../../../kernel/trace/trace.h"
+#include "internal.h"
+
+static int pstore_ftrace_enabled;
+static struct trace_array *pstore_ftrace_array;
+
+static void pstore_ftrace_call(unsigned long ip, unsigned long parent_ip)
+{
+	struct trace_array *tr = pstore_ftrace_array;
+	struct trace_array_cpu *data;
+	unsigned long flags;
+	long disabled;
+	int cpu;
+
+	smp_rmb();
+	if (unlikely(!pstore_ftrace_enabled))
+		return;
+
+	if (unlikely(oops_in_progress))
+		return;
+
+	/*
+	 * Need to use raw, since this must be called before the
+	 * recursive protection is performed.
+	 */
+	local_irq_save(flags);
+	cpu = raw_smp_processor_id();
+	data = tr->data[cpu];
+	disabled = atomic_inc_return(&data->disabled);
+
+	if (likely(disabled == 1)) {
+		struct pstore_ftrace_record rec = {};
+
+		rec.ip = ip;
+		rec.parent_ip = parent_ip;
+		pstore_ftrace_encode_cpu(&rec, cpu);
+		psinfo->write_buf(PSTORE_TYPE_FTRACE, 0, NULL, 0, (void *)&rec,
+				  sizeof(rec), psinfo);
+	}
+
+	atomic_dec(&data->disabled);
+	local_irq_restore(flags);
+}
+
+static struct ftrace_ops pstore_ftrace_ops __read_mostly = {
+	.func = pstore_ftrace_call,
+	.flags = FTRACE_OPS_FL_GLOBAL,
+};
+
+static int pstore_ftracer_init(struct trace_array *tr)
+{
+	if (!psinfo->write_buf) {
+		pr_info("%s: write_buf required, fix your backend\n", __func__);
+		return -ENOSYS;
+	}
+
+	pstore_ftrace_array = tr;
+	tr->cpu = get_cpu();
+	put_cpu();
+
+	tracing_start_cmdline_record();
+
+	pstore_ftrace_enabled = 0;
+	smp_wmb();
+
+	register_ftrace_function(&pstore_ftrace_ops);
+
+	smp_wmb();
+	pstore_ftrace_enabled = 1;
+	return 0;
+}
+
+static void pstore_ftrace_reset(struct trace_array *tr)
+{
+	pstore_ftrace_enabled = 0;
+	smp_wmb();
+
+	unregister_ftrace_function(&pstore_ftrace_ops);
+
+	tracing_stop_cmdline_record();
+}
+
+static void pstore_ftrace_start(struct trace_array *tr)
+{
+	tracing_reset_online_cpus(tr);
+}
+
+static struct tracer pstore_ftracer __read_mostly = {
+	.name		= "persistent",
+	.init		= pstore_ftracer_init,
+	.reset		= pstore_ftrace_reset,
+	.start		= pstore_ftrace_start,
+	.wait_pipe	= poll_wait_pipe,
+};
+
+void pstore_register_ftrace(void)
+{
+	int err;
+
+	err = register_tracer(&pstore_ftracer);
+	if (err)
+		pr_err("%s: failed to register tracer: %d\n", __func__, err);
+}
diff --git a/fs/pstore/inode.c b/fs/pstore/inode.c
index fda1331..5368b6d 100644
--- a/fs/pstore/inode.c
+++ b/fs/pstore/inode.c
@@ -27,6 +27,7 @@
 #include <linux/list.h>
 #include <linux/string.h>
 #include <linux/mount.h>
+#include <linux/seq_file.h>
 #include <linux/ramfs.h>
 #include <linux/parser.h>
 #include <linux/sched.h>
@@ -52,18 +53,117 @@ struct pstore_private {
 	char	data[];
 };
 
+struct pstore_ftrace_seq_data {
+	const void *ptr;
+	size_t off;
+	size_t size;
+};
+
+#define REC_SIZE sizeof(struct pstore_ftrace_record)
+
+static void *pstore_ftrace_seq_start(struct seq_file *s, loff_t *pos)
+{
+	struct pstore_private *ps = s->private;
+	struct pstore_ftrace_seq_data *data;
+
+	data = kzalloc(sizeof(*data), GFP_KERNEL);
+	if (!data)
+		return NULL;
+
+	data->off = ps->size % REC_SIZE;
+	data->off += *pos * REC_SIZE;
+	if (data->off + REC_SIZE > ps->size) {
+		kfree(data);
+		return NULL;
+	}
+
+	return data;
+
+}
+
+static void pstore_ftrace_seq_stop(struct seq_file *s, void *v)
+{
+	kfree(v);
+}
+
+static void *pstore_ftrace_seq_next(struct seq_file *s, void *v, loff_t *pos)
+{
+	struct pstore_private *ps = s->private;
+	struct pstore_ftrace_seq_data *data = v;
+
+	data->off += REC_SIZE;
+	if (data->off + REC_SIZE > ps->size)
+		return NULL;
+
+	(*pos)++;
+	return data;
+}
+
+static int pstore_ftrace_seq_show(struct seq_file *s, void *v)
+{
+	struct pstore_private *ps = s->private;
+	struct pstore_ftrace_seq_data *data = v;
+	struct pstore_ftrace_record *rec = (void *)(ps->data + data->off);
+
+	seq_printf(s, "%d %08lx  %08lx  %pf <- %pF\n",
+		pstore_ftrace_decode_cpu(rec), rec->ip, rec->parent_ip,
+		(void *)rec->ip, (void *)rec->parent_ip);
+
+	return 0;
+}
+
+static const struct seq_operations pstore_ftrace_seq_ops = {
+	.start	= pstore_ftrace_seq_start,
+	.next	= pstore_ftrace_seq_next,
+	.stop	= pstore_ftrace_seq_stop,
+	.show	= pstore_ftrace_seq_show,
+};
+
 static ssize_t pstore_file_read(struct file *file, char __user *userbuf,
 						size_t count, loff_t *ppos)
 {
-	struct pstore_private *ps = file->private_data;
+	struct seq_file *sf = file->private_data;
+	struct pstore_private *ps = sf->private;
 
+	if (ps->type == PSTORE_TYPE_FTRACE)
+		return seq_read(file, userbuf, count, ppos);
 	return simple_read_from_buffer(userbuf, count, ppos, ps->data, ps->size);
 }
 
+static int pstore_file_open(struct inode *inode, struct file *file)
+{
+	struct pstore_private *ps = inode->i_private;
+	struct seq_file *sf;
+	int err;
+	const struct seq_operations *sops = NULL;
+
+	if (ps->type == PSTORE_TYPE_FTRACE)
+		sops = &pstore_ftrace_seq_ops;
+
+	err = seq_open(file, sops);
+	if (err < 0)
+		return err;
+
+	sf = file->private_data;
+	sf->private = ps;
+
+	return 0;
+}
+
+static loff_t pstore_file_llseek(struct file *file, loff_t off, int origin)
+{
+	struct seq_file *sf = file->private_data;
+
+	if (sf->op)
+		return seq_lseek(file, off, origin);
+	return default_llseek(file, off, origin);
+}
+
 static const struct file_operations pstore_file_operations = {
-	.open	= simple_open,
-	.read	= pstore_file_read,
-	.llseek	= default_llseek,
+	.open		= pstore_file_open,
+	.read		= pstore_file_read,
+	.llseek		= pstore_file_llseek,
+	.release	= seq_release,
 };
 
 /*
@@ -215,6 +315,9 @@ int pstore_mkfile(enum pstore_type_id type, char *psname, u64 id,
 	case PSTORE_TYPE_CONSOLE:
 		sprintf(name, "console-%s", psname);
 		break;
+	case PSTORE_TYPE_FTRACE:
+		sprintf(name, "ftrace-%s", psname);
+		break;
 	case PSTORE_TYPE_MCE:
 		sprintf(name, "mce-%s-%lld", psname, id);
 		break;
diff --git a/fs/pstore/internal.h b/fs/pstore/internal.h
index 3bde461..6e09673 100644
--- a/fs/pstore/internal.h
+++ b/fs/pstore/internal.h
@@ -1,6 +1,55 @@
+#ifndef __PSTORE_INTERNAL_H__
+#define __PSTORE_INTERNAL_H__
+
+#include <linux/pstore.h>
+
+#if NR_CPUS <= 2 && defined(CONFIG_ARM_THUMB)
+#define PSTORE_CPU_IN_IP 0x1
+#elif NR_CPUS <= 4 && defined(CONFIG_ARM)
+#define PSTORE_CPU_IN_IP 0x3
+#endif
+
+struct pstore_ftrace_record {
+	unsigned long ip;
+	unsigned long parent_ip;
+#ifndef PSTORE_CPU_IN_IP
+	unsigned int cpu;
+#endif
+};
+
+static inline void
+pstore_ftrace_encode_cpu(struct pstore_ftrace_record *rec, unsigned int cpu)
+{
+#ifndef PSTORE_CPU_IN_IP
+	rec->cpu = cpu;
+#else
+	rec->ip |= cpu;
+#endif
+}
+
+static inline unsigned int
+pstore_ftrace_decode_cpu(struct pstore_ftrace_record *rec)
+{
+#ifndef PSTORE_CPU_IN_IP
+	return rec->cpu;
+#else
+	return rec->ip & PSTORE_CPU_IN_IP;
+#endif
+}
+
+#ifdef CONFIG_PSTORE_FTRACE
+extern void pstore_register_ftrace(void);
+#else
+static inline void pstore_register_ftrace(void) {}
+#endif
+
+extern struct pstore_info *psinfo;
+
 extern void	pstore_set_kmsg_bytes(int);
 extern void	pstore_get_records(int);
 extern int	pstore_mkfile(enum pstore_type_id, char *psname, u64 id,
 			      char *data, size_t size,
 			      struct timespec time, struct pstore_info *psi);
 extern int	pstore_is_mounted(void);
+
+#endif
diff --git a/fs/pstore/platform.c b/fs/pstore/platform.c
index e7c0a52..89995da 100644
--- a/fs/pstore/platform.c
+++ b/fs/pstore/platform.c
@@ -61,7 +61,7 @@ static DECLARE_WORK(pstore_work, pstore_dowork);
  * calls to pstore_register()
  */
 static DEFINE_SPINLOCK(pstore_lock);
-static struct pstore_info *psinfo;
+struct pstore_info *psinfo;
 
 static char *backend;
 
@@ -246,6 +246,7 @@ int pstore_register(struct pstore_info *psi)
 
 	kmsg_dump_register(&pstore_dumper);
 	pstore_register_console();
+	pstore_register_ftrace();
 
 	if (pstore_update_ms >= 0) {
 		pstore_timer.expires = jiffies +
diff --git a/include/linux/pstore.h b/include/linux/pstore.h
index b107484..23afffe 100644
--- a/include/linux/pstore.h
+++ b/include/linux/pstore.h
@@ -30,6 +30,7 @@ enum pstore_type_id {
 	PSTORE_TYPE_DMESG	= 0,
 	PSTORE_TYPE_MCE		= 1,
 	PSTORE_TYPE_CONSOLE	= 2,
+	PSTORE_TYPE_FTRACE	= 3,
 	PSTORE_TYPE_UNKNOWN	= 255
 };
 
-- 
1.7.9.2

[PATCH 4/5] pstore/ram: Convert to write_buf callback

[Anton Vorontsov]

Don't use pstore.buf directly, instead convert the code to write_buf callback
which passes a pointer to a buffer as an argument.

Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org>
---
 fs/pstore/ram.c |   17 +++++++++--------
 1 file changed, 9 insertions(+), 8 deletions(-)

diff --git a/fs/pstore/ram.c b/fs/pstore/ram.c
index c7acf94..96dbd1e 100644
--- a/fs/pstore/ram.c
+++ b/fs/pstore/ram.c
@@ -168,11 +168,12 @@ static size_t ramoops_write_kmsg_hdr(struct persistent_ram_zone *prz)
 	return len;
 }
 
-static int ramoops_pstore_write(enum pstore_type_id type,
-				enum kmsg_dump_reason reason,
-				u64 *id,
-				unsigned int part,
-				size_t size, struct pstore_info *psi)
+
+static int ramoops_pstore_write_buf(enum pstore_type_id type,
+				    enum kmsg_dump_reason reason,
+				    u64 *id, unsigned int part,
+				    const char *buf, size_t size,
+				    struct pstore_info *psi)
 {
 	struct ramoops_context *cxt = psi->data;
 	struct persistent_ram_zone *prz = cxt->przs[cxt->dump_write_cnt];
@@ -181,7 +182,7 @@ static int ramoops_pstore_write(enum pstore_type_id type,
 	if (type == PSTORE_TYPE_CONSOLE) {
 		if (!cxt->cprz)
 			return -ENOMEM;
-		persistent_ram_write(cxt->cprz, cxt->pstore.buf, size);
+		persistent_ram_write(cxt->cprz, buf, size);
 		return 0;
 	}
 
@@ -210,7 +211,7 @@ static int ramoops_pstore_write(enum pstore_type_id type,
 	hlen = ramoops_write_kmsg_hdr(prz);
 	if (size + hlen > prz->buffer_size)
 		size = prz->buffer_size - hlen;
-	persistent_ram_write(prz, cxt->pstore.buf, size);
+	persistent_ram_write(prz, buf, size);
 
 	cxt->dump_write_cnt = (cxt->dump_write_cnt + 1) % cxt->max_dump_cnt;
 
@@ -248,7 +249,7 @@ static struct ramoops_context oops_cxt = {
 		.name	= "ramoops",
 		.open	= ramoops_pstore_open,
 		.read	= ramoops_pstore_read,
-		.write	= ramoops_pstore_write,
+		.write_buf	= ramoops_pstore_write_buf,
 		.erase	= ramoops_pstore_erase,
 	},
 };
-- 
1.7.9.2

[PATCH 5/5] pstore/ram: Add ftrace messages handling

[Anton Vorontsov]

The ftrace log size is configurable via ramoops.ftrace_size
module option, and the log itself is available via
<pstore-mount>/ftrace-ramoops file.

Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org>
---
 Documentation/ramoops.txt  |   24 ++++++++++++++++++++++++
 fs/pstore/ram.c            |   37 +++++++++++++++++++++++++++++++++----
 include/linux/pstore_ram.h |    1 +
 3 files changed, 58 insertions(+), 4 deletions(-)

diff --git a/Documentation/ramoops.txt b/Documentation/ramoops.txt
index 59a74a8..dee307b 100644
--- a/Documentation/ramoops.txt
+++ b/Documentation/ramoops.txt
@@ -94,3 +94,27 @@ timestamp and a new line. The dump then continues with the actual data.
 The dump data can be read from the pstore filesystem. The format for these
 files is "dmesg-ramoops-N", where N is the record number in memory. To delete
 a stored record from RAM, simply unlink the respective pstore file.
+
+5. Persistent function tracing
+
+Persistent function tracing might be useful for debugging software or hardware
+related hangs. The functions call chain log is stored in a "ftrace-ramoops"
+file. Here is an example of usage:
+
+ # 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
diff --git a/fs/pstore/ram.c b/fs/pstore/ram.c
index 96dbd1e..018d895 100644
--- a/fs/pstore/ram.c
+++ b/fs/pstore/ram.c
@@ -45,6 +45,10 @@ static ulong ramoops_console_size = MIN_MEM_SIZE;
 module_param_named(console_size, ramoops_console_size, ulong, 0400);
 MODULE_PARM_DESC(console_size, "size of kernel console log");
 
+static ulong ramoops_ftrace_size = MIN_MEM_SIZE;
+module_param_named(ftrace_size, ramoops_ftrace_size, ulong, 0400);
+MODULE_PARM_DESC(ftrace_size, "size of ftrace log");
+
 static ulong mem_address;
 module_param(mem_address, ulong, 0400);
 MODULE_PARM_DESC(mem_address,
@@ -68,16 +72,19 @@ MODULE_PARM_DESC(ramoops_ecc,
 struct ramoops_context {
 	struct persistent_ram_zone **przs;
 	struct persistent_ram_zone *cprz;
+	struct persistent_ram_zone *fprz;
 	phys_addr_t phys_addr;
 	unsigned long size;
 	size_t record_size;
 	size_t console_size;
+	size_t ftrace_size;
 	int dump_oops;
 	bool ecc;
 	unsigned int max_dump_cnt;
 	unsigned int dump_write_cnt;
 	unsigned int dump_read_cnt;
 	unsigned int console_read_cnt;
+	unsigned int ftrace_read_cnt;
 	struct pstore_info pstore;
 };
 
@@ -136,6 +143,9 @@ static ssize_t ramoops_pstore_read(u64 *id, enum pstore_type_id *type,
 		prz = ramoops_get_next_prz(&cxt->cprz, &cxt->console_read_cnt,
 					   1, id, type, PSTORE_TYPE_CONSOLE, 0);
 	if (!prz)
+		prz = ramoops_get_next_prz(&cxt->fprz, &cxt->ftrace_read_cnt,
+					   1, id, type, PSTORE_TYPE_FTRACE, 0);
+	if (!prz)
 		return 0;
 
 	/* TODO(kees): Bogus time for the moment. */
@@ -184,6 +194,11 @@ static int ramoops_pstore_write_buf(enum pstore_type_id type,
 			return -ENOMEM;
 		persistent_ram_write(cxt->cprz, buf, size);
 		return 0;
+	} else if (type == PSTORE_TYPE_FTRACE) {
+		if (!cxt->fprz)
+			return -ENOMEM;
+		persistent_ram_write(cxt->fprz, buf, size);
+		return 0;
 	}
 
 	if (type != PSTORE_TYPE_DMESG)
@@ -233,6 +248,9 @@ static int ramoops_pstore_erase(enum pstore_type_id type, u64 id,
 	case PSTORE_TYPE_CONSOLE:
 		prz = cxt->cprz;
 		break;
+	case PSTORE_TYPE_FTRACE:
+		prz = cxt->fprz;
+		break;
 	default:
 		return -EINVAL;
 	}
@@ -346,7 +364,8 @@ static int __init ramoops_probe(struct platform_device *pdev)
 	if (cxt->max_dump_cnt)
 		goto fail_out;
 
-	if (!pdata->mem_size || (!pdata->record_size && !pdata->console_size)) {
+	if (!pdata->mem_size || (!pdata->record_size && !pdata->console_size &&
+			!pdata->ftrace_size)) {
 		pr_err("The memory size and the record/console size must be "
 			"non-zero\n");
 		goto fail_out;
@@ -355,18 +374,20 @@ static int __init ramoops_probe(struct platform_device *pdev)
 	pdata->mem_size = rounddown_pow_of_two(pdata->mem_size);
 	pdata->record_size = rounddown_pow_of_two(pdata->record_size);
 	pdata->console_size = rounddown_pow_of_two(pdata->console_size);
+	pdata->ftrace_size = rounddown_pow_of_two(pdata->ftrace_size);
 
 	cxt->dump_read_cnt = 0;
 	cxt->size = pdata->mem_size;
 	cxt->phys_addr = pdata->mem_address;
 	cxt->record_size = pdata->record_size;
 	cxt->console_size = pdata->console_size;
+	cxt->ftrace_size = pdata->ftrace_size;
 	cxt->dump_oops = pdata->dump_oops;
 	cxt->ecc = pdata->ecc;
 
 	paddr = cxt->phys_addr;
 
-	dump_mem_sz = cxt->size - cxt->console_size;
+	dump_mem_sz = cxt->size - cxt->console_size - cxt->ftrace_size;
 	err = ramoops_init_przs(dev, cxt, &paddr, dump_mem_sz);
 	if (err)
 		goto fail_out;
@@ -375,9 +396,14 @@ static int __init ramoops_probe(struct platform_device *pdev)
 	if (err)
 		goto fail_init_cprz;
 
-	if (!cxt->przs && !cxt->cprz) {
+	err = ramoops_init_prz(dev, cxt, &cxt->fprz, &paddr, cxt->ftrace_size);
+	if (err)
+		goto fail_init_fprz;
+
+	if (!cxt->przs && !cxt->cprz && !cxt->fprz) {
 		pr_err("memory size too small, minimum is %lu\n",
-			cxt->console_size + cxt->record_size);
+			cxt->console_size + cxt->record_size +
+			cxt->ftrace_size);
 		goto fail_cnt;
 	}
 
@@ -424,6 +450,8 @@ fail_clear:
 	cxt->pstore.bufsize = 0;
 	cxt->max_dump_cnt = 0;
 fail_cnt:
+	kfree(cxt->fprz);
+fail_init_fprz:
 	kfree(cxt->cprz);
 fail_init_cprz:
 	ramoops_free_przs(cxt);
@@ -478,6 +506,7 @@ static int __init ramoops_init(void)
 		dummy_data->mem_address = mem_address;
 		dummy_data->record_size = record_size;
 		dummy_data->console_size = ramoops_console_size;
+		dummy_data->ftrace_size = ramoops_ftrace_size;
 		dummy_data->dump_oops = dump_oops;
 		dummy_data->ecc = ramoops_ecc;
 		dummy = platform_create_bundle(&ramoops_driver, ramoops_probe,
diff --git a/include/linux/pstore_ram.h b/include/linux/pstore_ram.h
index 2470bb5..368da13 100644
--- a/include/linux/pstore_ram.h
+++ b/include/linux/pstore_ram.h
@@ -75,6 +75,7 @@ struct ramoops_platform_data {
 	unsigned long	mem_address;
 	unsigned long	record_size;
 	unsigned long	console_size;
+	unsigned long	ftrace_size;
 	int		dump_oops;
 	bool		ecc;
 };
-- 
1.7.9.2

Re: [PATCH 0/5] Function tracing support for pstore

[Steven Rostedt]

On Sat, 2012-05-26 at 06:34 -0700, Anton Vorontsov wrote:
> Hi all,
> 

Sorry for the late reply, Monday was US holiday, and I've been working
days on finding (and fixing) a very nasty bug.

> 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).
> 

Nice!

> 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)?
> 

What about making it a trace option? That is,
in .../debug/tracing/options, have 'persistent' and when that's
selected, we change to using the persistent buffer. This could be for
both function tracing and event tracing.

I'm currently working on getting 'multi' buffers working. I plan on
presenting it at Linux Plumbers for more feedback. But it will be adding
a lot of hooks that would probably make this rather trivial to
implement.

-- Steve

> 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,