From: Nathan Chancellor <nathan@kernel.org>
To: Jarmo Tiitto <jarmo.tiitto@gmail.com>,
Sami Tolvanen <samitolvanen@google.com>,
Bill Wendling <wcw@google.com>, Kees Cook <keescook@chromium.org>,
Nick Desaulniers <ndesaulniers@google.com>,
clang-built-linux@googlegroups.com, linux-kernel@vger.kernel.org
Cc: morbo@google.com
Subject: Re: [PATCH v2 1/1] pgo: Fix allocate_node() v2
Date: Thu, 3 Jun 2021 14:14:24 -0700 [thread overview]
Message-ID: <d7e94352-0b24-1ab1-8b54-b6ffd4347963@kernel.org> (raw)
In-Reply-To: <20210603133853.5383-1-jarmo.tiitto@gmail.com>
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 <jarmo.tiitto@gmail.com>
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 <nathan@kernel.org>
> ---
> 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
>
next prev parent reply other threads:[~2021-06-03 21:14 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-03 13:38 [PATCH v2 1/1] pgo: Fix allocate_node() v2 Jarmo Tiitto
2021-06-03 20:50 ` Nick Desaulniers
2021-06-03 20:52 ` Nathan Chancellor
2021-06-03 21:00 ` Nick Desaulniers
2021-06-03 21:14 ` Nathan Chancellor [this message]
2021-06-03 21:36 ` Kees Cook
2021-06-04 9:40 ` Jarmo Tiitto
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