Re: [PATCH v2 1/6] perf: Introduce extended syscall error reporting

[Alexander Shishkin]

Andy Shevchenko  writes:

> On Mon, Aug 24, 2015 at 5:32 PM, Alexander Shishkin
>  wrote:
>> +   /* trim the buffer to the supplied boundary */
>> +   len = strlen(buffer);
>> +   if (len >= attr->perf_err_size) {
>> +   len = attr->perf_err_size - 1;
>> +   buffer[len] = 0;
>> +   }
>
> len = strnlen(buffer, attr->perf_err_size);
> buffer[len] = 0;
>
> And perhaps perf_err_size has to be length (perf_err_len) ?
>
>> +
>> +   if (copy_to_user((void __user *)attr->perf_err, buffer, len + 1)) {
>> +   /* if we failed to copy once, don't bother later */
>> +   attr->perf_err_size = 0;
>
> Kaboom next time on buffer[-1] = 0; since len >= 0?

Of course, we never get here if attr::perf_err_size is 0, there's an
explicit check for that, but nice try.

Regards,
--
Alex
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Re: [PATCH v2 1/6] perf: Introduce extended syscall error reporting

[Alexander Shishkin]

Andy Shevchenko  writes:

> On Mon, Aug 24, 2015 at 5:32 PM, Alexander Shishkin
>  wrote:
>> +   /* trim the buffer to the supplied boundary */
>> +   len = strlen(buffer);
>> +   if (len >= attr->perf_err_size) {
>> +   len = attr->perf_err_size - 1;
>> +   buffer[len] = 0;
>> +   }
>
> len = strnlen(buffer, attr->perf_err_size);
> buffer[len] = 0;
>
> And perhaps perf_err_size has to be length (perf_err_len) ?
>
>> +
>> +   if (copy_to_user((void __user *)attr->perf_err, buffer, len + 1)) {
>> +   /* if we failed to copy once, don't bother later */
>> +   attr->perf_err_size = 0;
>
> Kaboom next time on buffer[-1] = 0; since len >= 0?

Of course, we never get here if attr::perf_err_size is 0, there's an
explicit check for that, but nice try.

Regards,
--
Alex
--
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Re: [PATCH v2 1/6] perf: Introduce extended syscall error reporting

[Andy Shevchenko]

On Mon, Aug 24, 2015 at 5:32 PM, Alexander Shishkin
 wrote:

One small comment below.

> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -49,6 +49,79 @@
>
>  #include 
>
> +static bool extended_reporting_enabled(struct perf_event_attr *attr)
> +{
> +   if (attr->size >= PERF_ATTR_SIZE_VER6 &&
> +   attr->perf_err_size > 0)
> +   return true;
> +
> +   return false;
> +}
> +
> +/*
> + * Provide a JSON formatted error report to the user if they asked for it.
> + */
> +static void perf_error_report_site(struct perf_event_attr *attr,
> +  const struct perf_err_site *site)
> +{
> +   unsigned long len;
> +   char *buffer;
> +
> +   if (!site || !extended_reporting_enabled(attr))
> +   return;
> +
> +   /* in case of nested perf_err()s, which you shouldn't really do */
> +   while (site->code <= -PERF_ERRNO)
> +   site = perf_errno_to_site(site->code);
> +
> +   buffer = kasprintf(GFP_KERNEL,
> +  "{\n"
> +  "\t\"code\": %d,\n"
> +  "\t\"module\": \"%s\",\n"
> +  "\t\"message\": \"%s\"\n"
> +  "}\n",
> +  site->code, site->owner, site->message
> +  );
> +   if (!buffer)
> +   return;
> +
> +   /* trim the buffer to the supplied boundary */
> +   len = strlen(buffer);
> +   if (len >= attr->perf_err_size) {
> +   len = attr->perf_err_size - 1;
> +   buffer[len] = 0;
> +   }

len = strnlen(buffer, attr->perf_err_size);
buffer[len] = 0;

And perhaps perf_err_size has to be length (perf_err_len) ?

> +
> +   if (copy_to_user((void __user *)attr->perf_err, buffer, len + 1)) {
> +   /* if we failed to copy once, don't bother later */
> +   attr->perf_err_size = 0;

Kaboom next time on buffer[-1] = 0; since len >= 0?

> +   }
> +
> +   kfree(buffer);
> +}

-- 
With Best Regards,
Andy Shevchenko
--
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Re: [PATCH v2 1/6] perf: Introduce extended syscall error reporting

[Andy Shevchenko]

On Mon, Aug 24, 2015 at 5:32 PM, Alexander Shishkin
 wrote:

One small comment below.

> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -49,6 +49,79 @@
>
>  #include 
>
> +static bool extended_reporting_enabled(struct perf_event_attr *attr)
> +{
> +   if (attr->size >= PERF_ATTR_SIZE_VER6 &&
> +   attr->perf_err_size > 0)
> +   return true;
> +
> +   return false;
> +}
> +
> +/*
> + * Provide a JSON formatted error report to the user if they asked for it.
> + */
> +static void perf_error_report_site(struct perf_event_attr *attr,
> +  const struct perf_err_site *site)
> +{
> +   unsigned long len;
> +   char *buffer;
> +
> +   if (!site || !extended_reporting_enabled(attr))
> +   return;
> +
> +   /* in case of nested perf_err()s, which you shouldn't really do */
> +   while (site->code <= -PERF_ERRNO)
> +   site = perf_errno_to_site(site->code);
> +
> +   buffer = kasprintf(GFP_KERNEL,
> +  "{\n"
> +  "\t\"code\": %d,\n"
> +  "\t\"module\": \"%s\",\n"
> +  "\t\"message\": \"%s\"\n"
> +  "}\n",
> +  site->code, site->owner, site->message
> +  );
> +   if (!buffer)
> +   return;
> +
> +   /* trim the buffer to the supplied boundary */
> +   len = strlen(buffer);
> +   if (len >= attr->perf_err_size) {
> +   len = attr->perf_err_size - 1;
> +   buffer[len] = 0;
> +   }

len = strnlen(buffer, attr->perf_err_size);
buffer[len] = 0;

And perhaps perf_err_size has to be length (perf_err_len) ?

> +
> +   if (copy_to_user((void __user *)attr->perf_err, buffer, len + 1)) {
> +   /* if we failed to copy once, don't bother later */
> +   attr->perf_err_size = 0;

Kaboom next time on buffer[-1] = 0; since len >= 0?

> +   }
> +
> +   kfree(buffer);
> +}

-- 
With Best Regards,
Andy Shevchenko
--
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[PATCH v2 1/6] perf: Introduce extended syscall error reporting

[Alexander Shishkin]

It has been pointed several times out that perf syscall error reporting
leaves a lot to be desired [1].

This patch introduces a fairly simple extension that allows call sites
to annotate their error codes with arbitrary strings, which will then
be copied to userspace (if they asked for it) along with the module
name that produced the error message in JSON format. This way, we can
provide both human-readable and machine-parsable information to user and
leave room for extensions in the future, such as file name and line
number if kernel debugging is enabled.

Each error "site" is referred to by its index, which is folded into an
integer error value within the range of [-PERF_ERRNO, -MAX_ERRNO], where
PERF_ERRNO is chosen to be below any known error codes, but still leaving
enough room to enumerate error sites. This way, all the traditional macros
will still handle these as error codes and we'd only have to convert them
to their original values right before returning to userspace. This way we
also don't have to worry about keeping a separate pointer to the error
message inside a perf_event.

[1] http://marc.info/?l=linux-kernel=141470811013082

Signed-off-by: Alexander Shishkin 
---
 include/linux/perf_event.h  | 71 ++
 include/uapi/linux/perf_event.h |  8 +++-
 kernel/events/core.c| 86 ++---
 3 files changed, 159 insertions(+), 6 deletions(-)

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 2027809433..8e37939d21 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -56,6 +56,77 @@ struct perf_guest_info_callbacks {
 #include 
 #include 
 
+#ifndef PERF_MODNAME
+#define PERF_MODNAME "perf"
+#endif
+
+/*
+ * Extended error reporting: annotate an error code with a string
+ * and a module name to help users diagnase problems with their
+ * attributes and whatnot.
+ */
+struct perf_err_site {
+   const char  *message;
+   const char  *owner;
+   const int   code;
+};
+
+#ifdef CONFIG_PERF_EVENTS
+
+/*
+ * Place all occurrences of struct perf_err_site into a special section,
+ * so that we can find out their offsets, which we'll use to refer back
+ * to the error sites.
+ */
+extern const struct perf_err_site __start___perf_err[], __stop___perf_err[];
+
+#define __perf_err(__c, __m) ({\
+   static struct perf_err_site \
+   __attribute__ ((__section__("__perf_err"))) \
+   __err_site = {  \
+   .message= (__m),\
+   .owner  = PERF_MODNAME, \
+   .code   = __builtin_constant_p((__c)) ? \
+   (__c) : -EINVAL,\
+   };  \
+   &__err_site;\
+})
+
+/*
+ * Use part of the [-1, -MAX_ERRNO] errno range for perf's extended error
+ * reporting. Anything within [-PERF_ERRNO, -MAX_ERRNO] is an index of a
+ * perf_err_site structure within __perf_err section. 3k should be enough
+ * for everybody, but let's add a boot-time warning just in case it overflows
+ * one day.
+ */
+#define PERF_ERRNO 1024
+
+static inline int perf_errno(const struct perf_err_site *site)
+{
+   unsigned long err = site - __start___perf_err;
+
+   return -(int)err - PERF_ERRNO;
+}
+
+static inline const struct perf_err_site *perf_errno_to_site(int err)
+{
+   return __start___perf_err - err - PERF_ERRNO;
+}
+
+#ifdef MODULE
+/*
+ * Module support is a tad trickier, but far from rocket surgery. Let's
+ * bypass it for now.
+ */
+#define perf_err(__c, __m) (__c)
+#else
+#define perf_err(__c, __m) (perf_errno(__perf_err((__c), (__m
+#endif
+
+#define PERF_ERR_PTR(__e, __m) (ERR_PTR(perf_err(__e, __m)))
+
+#endif
+
 struct perf_callchain_entry {
__u64   nr;
__u64   ip[PERF_MAX_STACK_DEPTH];
diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
index 2881145cda..73b6919954 100644
--- a/include/uapi/linux/perf_event.h
+++ b/include/uapi/linux/perf_event.h
@@ -264,6 +264,7 @@ enum perf_event_read_format {
/* add: sample_stack_user */
 #define PERF_ATTR_SIZE_VER4104 /* add: sample_regs_intr */
 #define PERF_ATTR_SIZE_VER5112 /* add: aux_watermark */
+#define PERF_ATTR_SIZE_VER6120 /* add: perf_err */
 
 /*
  * Hardware event_id to monitor via a performance monitoring event:
@@ -375,7 +376,12 @@ struct perf_event_attr {
 * Wakeup watermark for AUX area
 */
__u32   aux_watermark;
-   __u32   __reserved_2;   /* align to __u64 */
+
+   /*
+* Extended error reporting buffer
+*/
+   __u32   

[PATCH v2 1/6] perf: Introduce extended syscall error reporting

[Alexander Shishkin]

It has been pointed several times out that perf syscall error reporting
leaves a lot to be desired [1].

This patch introduces a fairly simple extension that allows call sites
to annotate their error codes with arbitrary strings, which will then
be copied to userspace (if they asked for it) along with the module
name that produced the error message in JSON format. This way, we can
provide both human-readable and machine-parsable information to user and
leave room for extensions in the future, such as file name and line
number if kernel debugging is enabled.

Each error site is referred to by its index, which is folded into an
integer error value within the range of [-PERF_ERRNO, -MAX_ERRNO], where
PERF_ERRNO is chosen to be below any known error codes, but still leaving
enough room to enumerate error sites. This way, all the traditional macros
will still handle these as error codes and we'd only have to convert them
to their original values right before returning to userspace. This way we
also don't have to worry about keeping a separate pointer to the error
message inside a perf_event.

[1] http://marc.info/?l=linux-kernelm=141470811013082

Signed-off-by: Alexander Shishkin alexander.shish...@linux.intel.com
---
 include/linux/perf_event.h  | 71 ++
 include/uapi/linux/perf_event.h |  8 +++-
 kernel/events/core.c| 86 ++---
 3 files changed, 159 insertions(+), 6 deletions(-)

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 2027809433..8e37939d21 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -56,6 +56,77 @@ struct perf_guest_info_callbacks {
 #include linux/cgroup.h
 #include asm/local.h
 
+#ifndef PERF_MODNAME
+#define PERF_MODNAME perf
+#endif
+
+/*
+ * Extended error reporting: annotate an error code with a string
+ * and a module name to help users diagnase problems with their
+ * attributes and whatnot.
+ */
+struct perf_err_site {
+   const char  *message;
+   const char  *owner;
+   const int   code;
+};
+
+#ifdef CONFIG_PERF_EVENTS
+
+/*
+ * Place all occurrences of struct perf_err_site into a special section,
+ * so that we can find out their offsets, which we'll use to refer back
+ * to the error sites.
+ */
+extern const struct perf_err_site __start___perf_err[], __stop___perf_err[];
+
+#define __perf_err(__c, __m) ({\
+   static struct perf_err_site \
+   __attribute__ ((__section__(__perf_err))) \
+   __err_site = {  \
+   .message= (__m),\
+   .owner  = PERF_MODNAME, \
+   .code   = __builtin_constant_p((__c)) ? \
+   (__c) : -EINVAL,\
+   };  \
+   __err_site;\
+})
+
+/*
+ * Use part of the [-1, -MAX_ERRNO] errno range for perf's extended error
+ * reporting. Anything within [-PERF_ERRNO, -MAX_ERRNO] is an index of a
+ * perf_err_site structure within __perf_err section. 3k should be enough
+ * for everybody, but let's add a boot-time warning just in case it overflows
+ * one day.
+ */
+#define PERF_ERRNO 1024
+
+static inline int perf_errno(const struct perf_err_site *site)
+{
+   unsigned long err = site - __start___perf_err;
+
+   return -(int)err - PERF_ERRNO;
+}
+
+static inline const struct perf_err_site *perf_errno_to_site(int err)
+{
+   return __start___perf_err - err - PERF_ERRNO;
+}
+
+#ifdef MODULE
+/*
+ * Module support is a tad trickier, but far from rocket surgery. Let's
+ * bypass it for now.
+ */
+#define perf_err(__c, __m) (__c)
+#else
+#define perf_err(__c, __m) (perf_errno(__perf_err((__c), (__m
+#endif
+
+#define PERF_ERR_PTR(__e, __m) (ERR_PTR(perf_err(__e, __m)))
+
+#endif
+
 struct perf_callchain_entry {
__u64   nr;
__u64   ip[PERF_MAX_STACK_DEPTH];
diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
index 2881145cda..73b6919954 100644
--- a/include/uapi/linux/perf_event.h
+++ b/include/uapi/linux/perf_event.h
@@ -264,6 +264,7 @@ enum perf_event_read_format {
/* add: sample_stack_user */
 #define PERF_ATTR_SIZE_VER4104 /* add: sample_regs_intr */
 #define PERF_ATTR_SIZE_VER5112 /* add: aux_watermark */
+#define PERF_ATTR_SIZE_VER6120 /* add: perf_err */
 
 /*
  * Hardware event_id to monitor via a performance monitoring event:
@@ -375,7 +376,12 @@ struct perf_event_attr {
 * Wakeup watermark for AUX area
 */
__u32   aux_watermark;
-   __u32   __reserved_2;   /* align to __u64 */
+
+   /*
+* Extended