Based on Kees and others feedback here is v2 patch
that clarifies why the current checks in allocate_node()
are flawed. I did fair amount of KGDB time on it.
When clang instrumentation eventually calls allocate_node()
the struct llvm_prf_data *p argument tells us from what section
we should reserve the vnode: It either points into vmlinux's
core __llvm_prf_data section or some loaded module's
__llvm_prf_data section.
But since we don't have access to corresponding
__llvm_prf_vnds section(s) for any module, the function
should return just NULL and ignore any profiling attempts
from modules for now.
Signed-off-by: Jarmo Tiitto <[email protected]>
---
kernel/pgo/instrument.c | 21 ++++++++++++---------
1 file changed, 12 insertions(+), 9 deletions(-)
diff --git a/kernel/pgo/instrument.c b/kernel/pgo/instrument.c
index 0e07ee1b17d9..afe9982b07a3 100644
--- a/kernel/pgo/instrument.c
+++ b/kernel/pgo/instrument.c
@@ -23,6 +23,7 @@
#include <linux/export.h>
#include <linux/spinlock.h>
#include <linux/types.h>
+#include <asm-generic/sections.h>
#include "pgo.h"
/*
@@ -55,17 +56,19 @@ void prf_unlock(unsigned long flags)
static struct llvm_prf_value_node *allocate_node(struct llvm_prf_data *p,
u32 index, u64 value)
{
- if (&__llvm_prf_vnds_start[current_node + 1] >= __llvm_prf_vnds_end)
- return NULL; /* Out of nodes */
-
- current_node++;
-
- /* Make sure the node is entirely within the section */
- if (&__llvm_prf_vnds_start[current_node] >= __llvm_prf_vnds_end ||
- &__llvm_prf_vnds_start[current_node + 1] > __llvm_prf_vnds_end)
+ const int max_vnds = prf_vnds_count();
+ /* Check that p is within vmlinux __llvm_prf_data section.
+ * If not, don't allocate since we can't handle modules yet.
+ */
+ if (!memory_contains(__llvm_prf_data_start,
+ __llvm_prf_data_end, p, sizeof(*p)))
return NULL;
- return &__llvm_prf_vnds_start[current_node];
+ if (WARN_ON_ONCE(current_node >= max_vnds))
+ return NULL; /* Out of nodes */
+
+ /* reserve vnode for vmlinux */
+ return &__llvm_prf_vnds_start[current_node++];
}
/*
base-commit: 5d0cda65918279ada060417c5fecb7e86ccb3def
--
2.31.1
On Thu, Jun 3, 2021 at 6:41 AM Jarmo Tiitto <[email protected]> wrote:
>
> Based on Kees and others feedback here is v2 patch
> that clarifies why the current checks in allocate_node()
> are flawed. I did fair amount of KGDB time on it.
Kees can probably cut it when merging, but the above paragraph might
be better "below the fold" below next time (doesn't necessitate a v3).
>
> When clang instrumentation eventually calls allocate_node()
> the struct llvm_prf_data *p argument tells us from what section
> we should reserve the vnode: It either points into vmlinux's
> core __llvm_prf_data section or some loaded module's
> __llvm_prf_data section.
>
> But since we don't have access to corresponding
> __llvm_prf_vnds section(s) for any module, the function
> should return just NULL and ignore any profiling attempts
> from modules for now.
>
> Signed-off-by: Jarmo Tiitto <[email protected]>
> ---
^ ie. here. If you put text between the `---` and the diffstat, git
just discards it when applying. It's a good way to hide commentary
just meant for reviewers when sending a patch.
> kernel/pgo/instrument.c | 21 ++++++++++++---------
> 1 file changed, 12 insertions(+), 9 deletions(-)
>
> diff --git a/kernel/pgo/instrument.c b/kernel/pgo/instrument.c
> index 0e07ee1b17d9..afe9982b07a3 100644
> --- a/kernel/pgo/instrument.c
> +++ b/kernel/pgo/instrument.c
> @@ -23,6 +23,7 @@
> #include <linux/export.h>
> #include <linux/spinlock.h>
> #include <linux/types.h>
> +#include <asm-generic/sections.h>
> #include "pgo.h"
>
> /*
> @@ -55,17 +56,19 @@ void prf_unlock(unsigned long flags)
> static struct llvm_prf_value_node *allocate_node(struct llvm_prf_data *p,
> u32 index, u64 value)
> {
> - if (&__llvm_prf_vnds_start[current_node + 1] >= __llvm_prf_vnds_end)
> - return NULL; /* Out of nodes */
> -
> - current_node++;
> -
> - /* Make sure the node is entirely within the section */
> - if (&__llvm_prf_vnds_start[current_node] >= __llvm_prf_vnds_end ||
> - &__llvm_prf_vnds_start[current_node + 1] > __llvm_prf_vnds_end)
> + const int max_vnds = prf_vnds_count();
Sorry, where was prf_vnds_count() defined? I don't see it in
linux-next, but I'm also not sure which tree has
5d0cda65918279ada060417c5fecb7e86ccb3def.
> + /* Check that p is within vmlinux __llvm_prf_data section.
> + * If not, don't allocate since we can't handle modules yet.
> + */
> + if (!memory_contains(__llvm_prf_data_start,
> + __llvm_prf_data_end, p, sizeof(*p)))
> return NULL;
>
> - return &__llvm_prf_vnds_start[current_node];
> + if (WARN_ON_ONCE(current_node >= max_vnds))
> + return NULL; /* Out of nodes */
> +
> + /* reserve vnode for vmlinux */
> + return &__llvm_prf_vnds_start[current_node++];
> }
>
> /*
>
> base-commit: 5d0cda65918279ada060417c5fecb7e86ccb3def
> --
> 2.31.1
>
--
Thanks,
~Nick Desaulniers
On 6/3/2021 1:50 PM, Nick Desaulniers wrote:
> On Thu, Jun 3, 2021 at 6:41 AM Jarmo Tiitto <[email protected]> wrote:
>>
>> Based on Kees and others feedback here is v2 patch
>> that clarifies why the current checks in allocate_node()
>> are flawed. I did fair amount of KGDB time on it.
>
> Kees can probably cut it when merging, but the above paragraph might
> be better "below the fold" below next time (doesn't necessitate a v3).
>
>>
>> When clang instrumentation eventually calls allocate_node()
>> the struct llvm_prf_data *p argument tells us from what section
>> we should reserve the vnode: It either points into vmlinux's
>> core __llvm_prf_data section or some loaded module's
>> __llvm_prf_data section.
>>
>> But since we don't have access to corresponding
>> __llvm_prf_vnds section(s) for any module, the function
>> should return just NULL and ignore any profiling attempts
>> from modules for now.
>>
>> Signed-off-by: Jarmo Tiitto <[email protected]>
>> ---
>
> ^ ie. here. If you put text between the `---` and the diffstat, git
> just discards it when applying. It's a good way to hide commentary
> just meant for reviewers when sending a patch.
>
>
>> kernel/pgo/instrument.c | 21 ++++++++++++---------
>> 1 file changed, 12 insertions(+), 9 deletions(-)
>>
>> diff --git a/kernel/pgo/instrument.c b/kernel/pgo/instrument.c
>> index 0e07ee1b17d9..afe9982b07a3 100644
>> --- a/kernel/pgo/instrument.c
>> +++ b/kernel/pgo/instrument.c
>> @@ -23,6 +23,7 @@
>> #include <linux/export.h>
>> #include <linux/spinlock.h>
>> #include <linux/types.h>
>> +#include <asm-generic/sections.h>
>> #include "pgo.h"
>>
>> /*
>> @@ -55,17 +56,19 @@ void prf_unlock(unsigned long flags)
>> static struct llvm_prf_value_node *allocate_node(struct llvm_prf_data *p,
>> u32 index, u64 value)
>> {
>> - if (&__llvm_prf_vnds_start[current_node + 1] >= __llvm_prf_vnds_end)
>> - return NULL; /* Out of nodes */
>> -
>> - current_node++;
>> -
>> - /* Make sure the node is entirely within the section */
>> - if (&__llvm_prf_vnds_start[current_node] >= __llvm_prf_vnds_end ||
>> - &__llvm_prf_vnds_start[current_node + 1] > __llvm_prf_vnds_end)
>> + const int max_vnds = prf_vnds_count();
>
> Sorry, where was prf_vnds_count() defined? I don't see it in
> linux-next, but I'm also not sure which tree has
> 5d0cda65918279ada060417c5fecb7e86ccb3def.
It is generated via the __DEFINE_PRF_SIZE macro in kernel/pgo/pgo.h.
>> + /* Check that p is within vmlinux __llvm_prf_data section.
>> + * If not, don't allocate since we can't handle modules yet.
>> + */
>> + if (!memory_contains(__llvm_prf_data_start,
>> + __llvm_prf_data_end, p, sizeof(*p)))
>> return NULL;
>>
>> - return &__llvm_prf_vnds_start[current_node];
>> + if (WARN_ON_ONCE(current_node >= max_vnds))
>> + return NULL; /* Out of nodes */
>> +
>> + /* reserve vnode for vmlinux */
>> + return &__llvm_prf_vnds_start[current_node++];
>> }
>>
>> /*
>>
>> base-commit: 5d0cda65918279ada060417c5fecb7e86ccb3def
>> --
>> 2.31.1
>>
>
>
> --
> Thanks,
> ~Nick Desaulniers
>
On Thu, Jun 3, 2021 at 1:52 PM Nathan Chancellor <[email protected]> wrote:
>
> On 6/3/2021 1:50 PM, Nick Desaulniers wrote:
> > On Thu, Jun 3, 2021 at 6:41 AM Jarmo Tiitto <[email protected]> wrote:
> >>
> >> Based on Kees and others feedback here is v2 patch
> >> that clarifies why the current checks in allocate_node()
> >> are flawed. I did fair amount of KGDB time on it.
> >
> > Kees can probably cut it when merging, but the above paragraph might
> > be better "below the fold" below next time (doesn't necessitate a v3).
> >
> >>
> >> When clang instrumentation eventually calls allocate_node()
> >> the struct llvm_prf_data *p argument tells us from what section
> >> we should reserve the vnode: It either points into vmlinux's
> >> core __llvm_prf_data section or some loaded module's
> >> __llvm_prf_data section.
> >>
> >> But since we don't have access to corresponding
> >> __llvm_prf_vnds section(s) for any module, the function
> >> should return just NULL and ignore any profiling attempts
> >> from modules for now.
> >>
> >> Signed-off-by: Jarmo Tiitto <[email protected]>
> >> ---
> >
> > ^ ie. here. If you put text between the `---` and the diffstat, git
> > just discards it when applying. It's a good way to hide commentary
> > just meant for reviewers when sending a patch.
> >
> >
> >> kernel/pgo/instrument.c | 21 ++++++++++++---------
> >> 1 file changed, 12 insertions(+), 9 deletions(-)
> >>
> >> diff --git a/kernel/pgo/instrument.c b/kernel/pgo/instrument.c
> >> index 0e07ee1b17d9..afe9982b07a3 100644
> >> --- a/kernel/pgo/instrument.c
> >> +++ b/kernel/pgo/instrument.c
> >> @@ -23,6 +23,7 @@
> >> #include <linux/export.h>
> >> #include <linux/spinlock.h>
> >> #include <linux/types.h>
> >> +#include <asm-generic/sections.h>
> >> #include "pgo.h"
> >>
> >> /*
> >> @@ -55,17 +56,19 @@ void prf_unlock(unsigned long flags)
> >> static struct llvm_prf_value_node *allocate_node(struct llvm_prf_data *p,
> >> u32 index, u64 value)
> >> {
> >> - if (&__llvm_prf_vnds_start[current_node + 1] >= __llvm_prf_vnds_end)
> >> - return NULL; /* Out of nodes */
> >> -
> >> - current_node++;
> >> -
> >> - /* Make sure the node is entirely within the section */
> >> - if (&__llvm_prf_vnds_start[current_node] >= __llvm_prf_vnds_end ||
> >> - &__llvm_prf_vnds_start[current_node + 1] > __llvm_prf_vnds_end)
> >> + const int max_vnds = prf_vnds_count();
> >
> > Sorry, where was prf_vnds_count() defined? I don't see it in
> > linux-next, but I'm also not sure which tree has
> > 5d0cda65918279ada060417c5fecb7e86ccb3def.
>
> It is generated via the __DEFINE_PRF_SIZE macro in kernel/pgo/pgo.h.
Thanks, it kills me when I can't find something with grep. I wonder if
language servers more modern than ctags have figured this out yet.
Patch looks fine to me then.
Reviewed-by: Nick Desaulniers <[email protected]>
>
> >> + /* Check that p is within vmlinux __llvm_prf_data section.
> >> + * If not, don't allocate since we can't handle modules yet.
> >> + */
> >> + if (!memory_contains(__llvm_prf_data_start,
> >> + __llvm_prf_data_end, p, sizeof(*p)))
> >> return NULL;
> >>
> >> - return &__llvm_prf_vnds_start[current_node];
> >> + if (WARN_ON_ONCE(current_node >= max_vnds))
> >> + return NULL; /* Out of nodes */
> >> +
> >> + /* reserve vnode for vmlinux */
> >> + return &__llvm_prf_vnds_start[current_node++];
> >> }
> >>
> >> /*
> >>
> >> base-commit: 5d0cda65918279ada060417c5fecb7e86ccb3def
> >> --
> >> 2.31.1
> >>
> >
> >
> > --
> > Thanks,
> > ~Nick Desaulniers
> >
>
> --
> You received this message because you are subscribed to the Google Groups "Clang Built Linux" group.
> To unsubscribe from this group and stop receiving emails from it, send an email to [email protected].
> To view this discussion on the web visit https://groups.google.com/d/msgid/clang-built-linux/f06200fd-4ce5-e976-20ec-d2ea9d734b3c%40kernel.org.
--
Thanks,
~Nick Desaulniers
On 6/3/2021 6:38 AM, Jarmo Tiitto wrote:
> Based on Kees and others feedback here is v2 patch
> that clarifies why the current checks in allocate_node()
> are flawed. I did fair amount of KGDB time on it.
>
> When clang instrumentation eventually calls allocate_node()
> the struct llvm_prf_data *p argument tells us from what section
> we should reserve the vnode: It either points into vmlinux's
> core __llvm_prf_data section or some loaded module's
> __llvm_prf_data section.
>
> But since we don't have access to corresponding
> __llvm_prf_vnds section(s) for any module, the function
> should return just NULL and ignore any profiling attempts
> from modules for now.
>
> Signed-off-by: Jarmo Tiitto <[email protected]>
I agree with Nick on the comments about the commit message. A few more
small nits below, not sure they necessitate a v3, up to you. Thank you
for the patch!
Reviewed-by: Nathan Chancellor <[email protected]>
> ---
> kernel/pgo/instrument.c | 21 ++++++++++++---------
> 1 file changed, 12 insertions(+), 9 deletions(-)
>
> diff --git a/kernel/pgo/instrument.c b/kernel/pgo/instrument.c
> index 0e07ee1b17d9..afe9982b07a3 100644
> --- a/kernel/pgo/instrument.c
> +++ b/kernel/pgo/instrument.c
> @@ -23,6 +23,7 @@
> #include <linux/export.h>
> #include <linux/spinlock.h>
> #include <linux/types.h>
> +#include <asm-generic/sections.h>
Not sure that it actually matters but I think this should be
#include <asm/sections.h>
instead. Might be nice to keep this sorted by moving it to the top as well.
> #include "pgo.h"
>
> /*
> @@ -55,17 +56,19 @@ void prf_unlock(unsigned long flags)
> static struct llvm_prf_value_node *allocate_node(struct llvm_prf_data *p,
> u32 index, u64 value)
> {
> - if (&__llvm_prf_vnds_start[current_node + 1] >= __llvm_prf_vnds_end)
> - return NULL; /* Out of nodes */
> -
> - current_node++;
> -
> - /* Make sure the node is entirely within the section */
> - if (&__llvm_prf_vnds_start[current_node] >= __llvm_prf_vnds_end ||
> - &__llvm_prf_vnds_start[current_node + 1] > __llvm_prf_vnds_end)
> + const int max_vnds = prf_vnds_count();
A blank line between this variable and the comment below would look nice.
> + /* Check that p is within vmlinux __llvm_prf_data section. > + * If not, don't allocate since we can't handle modules yet.
> + */
For every subsystem except for netdev, there should be a blank line at
the beginning of a comment. In other works:
/*
* Check that p is within vmlinux __llvm_prf_data section.
* If not, don't allocate since we can't handle modules yet.
*/
> + if (!memory_contains(__llvm_prf_data_start,
> + __llvm_prf_data_end, p, sizeof(*p)))
> return NULL;
>
> - return &__llvm_prf_vnds_start[current_node];
> + if (WARN_ON_ONCE(current_node >= max_vnds))
> + return NULL; /* Out of nodes */
> +
> + /* reserve vnode for vmlinux */
> + return &__llvm_prf_vnds_start[current_node++];
> }
>
> /*
>
> base-commit: 5d0cda65918279ada060417c5fecb7e86ccb3def
>
On Thu, Jun 03, 2021 at 02:14:24PM -0700, Nathan Chancellor wrote:
> On 6/3/2021 6:38 AM, Jarmo Tiitto wrote:
> > Based on Kees and others feedback here is v2 patch
> > that clarifies why the current checks in allocate_node()
> > are flawed. I did fair amount of KGDB time on it.
> >
> > When clang instrumentation eventually calls allocate_node()
> > the struct llvm_prf_data *p argument tells us from what section
> > we should reserve the vnode: It either points into vmlinux's
> > core __llvm_prf_data section or some loaded module's
> > __llvm_prf_data section.
> >
> > But since we don't have access to corresponding
> > __llvm_prf_vnds section(s) for any module, the function
> > should return just NULL and ignore any profiling attempts
> > from modules for now.
> >
> > Signed-off-by: Jarmo Tiitto <[email protected]>
>
> I agree with Nick on the comments about the commit message. A few more small
> nits below, not sure they necessitate a v3, up to you. Thank you for the
> patch!
It would make my life easier to get a v3. :) I agree with all of
Nathan's suggestions. :)
Thanks!
-Kees
--
Kees Cook
Kees Cook wrote perjantaina 4. kesäkuuta 2021 0.36.39 EEST:
> On Thu, Jun 03, 2021 at 02:14:24PM -0700, Nathan Chancellor wrote:
> > On 6/3/2021 6:38 AM, Jarmo Tiitto wrote:
> > > Based on Kees and others feedback here is v2 patch
> > > that clarifies why the current checks in allocate_node()
> > > are flawed. I did fair amount of KGDB time on it.
> > >
> > > When clang instrumentation eventually calls allocate_node()
> > > the struct llvm_prf_data *p argument tells us from what section
> > > we should reserve the vnode: It either points into vmlinux's
> > > core __llvm_prf_data section or some loaded module's
> > > __llvm_prf_data section.
> > >
> > > But since we don't have access to corresponding
> > > __llvm_prf_vnds section(s) for any module, the function
> > > should return just NULL and ignore any profiling attempts
> > > from modules for now.
> > >
> > > Signed-off-by: Jarmo Tiitto <[email protected]>
> >
> > I agree with Nick on the comments about the commit message. A few more small
> > nits below, not sure they necessitate a v3, up to you. Thank you for the
> > patch!
>
> It would make my life easier to get a v3. :) I agree with all of
> Nathan's suggestions. :)
>
> Thanks!
>
> -Kees
>
> --
> Kees Cook
>
Hello,
Ok, I'll make the requested changes, noted by Nathan and post v3 patch soon. :-)
Btw. These patches were based on kees/for-next/clang/features branch.
Thanks for patience.
-Jarmo