Re: [PATCH 11/13] proc: readdir /proc/*/task
On Wed, Aug 29, 2018 at 04:43:30PM -0700, Andrew Morton wrote: > On Tue, 28 Aug 2018 22:35:02 +0300 Alexey Dobriyan > wrote: > > > > Are we really in a super hot path to justify all that? > > > > /proc is very slow, try profiling just about anything involving /proc. > > So how much does this patchset help? Some timing measurements would > really help things along, if they show goodness. Benchmarking results are in individual patches. They are ~1-7-20% better overall. However those are microbenchmarks.
Re: [PATCH 11/13] proc: readdir /proc/*/task
On Wed, Aug 29, 2018 at 04:43:30PM -0700, Andrew Morton wrote: > On Tue, 28 Aug 2018 22:35:02 +0300 Alexey Dobriyan > wrote: > > > > Are we really in a super hot path to justify all that? > > > > /proc is very slow, try profiling just about anything involving /proc. > > So how much does this patchset help? Some timing measurements would > really help things along, if they show goodness. Benchmarking results are in individual patches. They are ~1-7-20% better overall. However those are microbenchmarks.
Re: [PATCH 11/13] proc: readdir /proc/*/task
On Tue, 28 Aug 2018 22:35:02 +0300 Alexey Dobriyan wrote: > > Are we really in a super hot path to justify all that? > > /proc is very slow, try profiling just about anything involving /proc. So how much does this patchset help? Some timing measurements would really help things along, if they show goodness.
Re: [PATCH 11/13] proc: readdir /proc/*/task
On Tue, 28 Aug 2018 22:35:02 +0300 Alexey Dobriyan wrote: > > Are we really in a super hot path to justify all that? > > /proc is very slow, try profiling just about anything involving /proc. So how much does this patchset help? Some timing measurements would really help things along, if they show goodness.
Re: [PATCH 11/13] proc: readdir /proc/*/task
On Tue, Aug 28, 2018 at 01:04:40PM +, Ahmed S. Darwish wrote:
> On Tue, Aug 28, 2018 at 12:36:22PM +, Ahmed S. Darwish wrote:
> > On Tue, Aug 28, 2018 at 02:15:01AM +0300, Alexey Dobriyan wrote:
> > > ---
> > > fs/proc/base.c | 8
> > > 1 file changed, 4 insertions(+), 4 deletions(-)
> > >
> >
> > Missing description and S-o-b. Further comments below..
> >
> > > diff --git a/fs/proc/base.c b/fs/proc/base.c
> > > index 33f444721965..668e465c86b3 100644
> > > --- a/fs/proc/base.c
> > > +++ b/fs/proc/base.c
> > > @@ -3549,11 +3549,11 @@ static int proc_task_readdir(struct file *file,
> > > struct dir_context *ctx)
> > > for (task = first_tid(proc_pid(inode), tid, ctx->pos - 2, ns);
> > >task;
> > >task = next_tid(task), ctx->pos++) {
> > > - char name[10 + 1];
> > > - unsigned int len;
> > > + char name[10], *p = name + sizeof(name);
> > > +
> >
> > Multiple issues:
> >
> > - len should be 11, as was in the original code
> > (0x = 4294967295, 10 letters)
> >
> > - while we're at it, let's use a constant for the '11' instead of
> > mysterious magic numbers
> >
> > - 'p' is clearly overflowing the stack here
> >
>
> See below:
>
> > > tid = task_pid_nr_ns(task, ns);
> > > - len = snprintf(name, sizeof(name), "%u", tid);
> > > - if (!proc_fill_cache(file, ctx, name, len,
> > > + p = _print_integer_u32(p, tid);
> > > + if (!proc_fill_cache(file, ctx, p, name + sizeof(name) - p,
> >
> > You're replacing snprintf() code __that did proper len checking__
> > with code that does not. That's not good.
> >
> > I can't see how the fourth proc_fill_cache() parameter, ``name +
> > sizeof(name)'' safely ever replace the original 'len' parameter.
> > It's a pointer value .. (!)
> >
>
> Ok, there's a "- p" in the end, so the length looks to be Ok.
>
> Nonetheless, the whole patch series is introducing funny code
> like:
>
> +/*
> + * Print an integer in decimal.
> + * "p" initially points PAST THE END OF THE BUFFER!
> + *
> + * DO NOT USE THESE FUNCTIONS!
> + *
> + * Do not copy these functions.
> + * Do not document these functions.
> + * Do not move these functions to lib/ or elsewhere.
> + * Do not export these functions to modules.
> + * Do not tell anyone about these functions.
> + */
> +noinline
> +char *_print_integer_u32(char *p, u32 x)
> +{
> + do {
> + *--p = '0' + (x % 10);
> + x /= 10;
> + } while (x != 0);
> + return p;
> +}
>
> And thus the code using these functions is throwing invalid
> past-the-stack pointers and strings with no NULL terminators
> like there's no tomorrow...
>
> IMHO It's an accident waiting to happen to sprinkle pointers
> like that everywhere.
It is not if people will be prohibited from moving this code to lib/ and
"improving" it by adding more parameters.
> Are we really in a super hot path to justify all that?
/proc is very slow, try profiling just about anything involving /proc.
Re: [PATCH 11/13] proc: readdir /proc/*/task
On Tue, Aug 28, 2018 at 01:04:40PM +, Ahmed S. Darwish wrote:
> On Tue, Aug 28, 2018 at 12:36:22PM +, Ahmed S. Darwish wrote:
> > On Tue, Aug 28, 2018 at 02:15:01AM +0300, Alexey Dobriyan wrote:
> > > ---
> > > fs/proc/base.c | 8
> > > 1 file changed, 4 insertions(+), 4 deletions(-)
> > >
> >
> > Missing description and S-o-b. Further comments below..
> >
> > > diff --git a/fs/proc/base.c b/fs/proc/base.c
> > > index 33f444721965..668e465c86b3 100644
> > > --- a/fs/proc/base.c
> > > +++ b/fs/proc/base.c
> > > @@ -3549,11 +3549,11 @@ static int proc_task_readdir(struct file *file,
> > > struct dir_context *ctx)
> > > for (task = first_tid(proc_pid(inode), tid, ctx->pos - 2, ns);
> > >task;
> > >task = next_tid(task), ctx->pos++) {
> > > - char name[10 + 1];
> > > - unsigned int len;
> > > + char name[10], *p = name + sizeof(name);
> > > +
> >
> > Multiple issues:
> >
> > - len should be 11, as was in the original code
> > (0x = 4294967295, 10 letters)
> >
> > - while we're at it, let's use a constant for the '11' instead of
> > mysterious magic numbers
> >
> > - 'p' is clearly overflowing the stack here
> >
>
> See below:
>
> > > tid = task_pid_nr_ns(task, ns);
> > > - len = snprintf(name, sizeof(name), "%u", tid);
> > > - if (!proc_fill_cache(file, ctx, name, len,
> > > + p = _print_integer_u32(p, tid);
> > > + if (!proc_fill_cache(file, ctx, p, name + sizeof(name) - p,
> >
> > You're replacing snprintf() code __that did proper len checking__
> > with code that does not. That's not good.
> >
> > I can't see how the fourth proc_fill_cache() parameter, ``name +
> > sizeof(name)'' safely ever replace the original 'len' parameter.
> > It's a pointer value .. (!)
> >
>
> Ok, there's a "- p" in the end, so the length looks to be Ok.
>
> Nonetheless, the whole patch series is introducing funny code
> like:
>
> +/*
> + * Print an integer in decimal.
> + * "p" initially points PAST THE END OF THE BUFFER!
> + *
> + * DO NOT USE THESE FUNCTIONS!
> + *
> + * Do not copy these functions.
> + * Do not document these functions.
> + * Do not move these functions to lib/ or elsewhere.
> + * Do not export these functions to modules.
> + * Do not tell anyone about these functions.
> + */
> +noinline
> +char *_print_integer_u32(char *p, u32 x)
> +{
> + do {
> + *--p = '0' + (x % 10);
> + x /= 10;
> + } while (x != 0);
> + return p;
> +}
>
> And thus the code using these functions is throwing invalid
> past-the-stack pointers and strings with no NULL terminators
> like there's no tomorrow...
>
> IMHO It's an accident waiting to happen to sprinkle pointers
> like that everywhere.
It is not if people will be prohibited from moving this code to lib/ and
"improving" it by adding more parameters.
> Are we really in a super hot path to justify all that?
/proc is very slow, try profiling just about anything involving /proc.
Re: [PATCH 11/13] proc: readdir /proc/*/task
On Tue, Aug 28, 2018 at 12:36:22PM +, Ahmed S. Darwish wrote:
> On Tue, Aug 28, 2018 at 02:15:01AM +0300, Alexey Dobriyan wrote:
> > ---
> > fs/proc/base.c | 8
> > 1 file changed, 4 insertions(+), 4 deletions(-)
> >
>
> Missing description and S-o-b. Further comments below..
>
> > diff --git a/fs/proc/base.c b/fs/proc/base.c
> > index 33f444721965..668e465c86b3 100644
> > --- a/fs/proc/base.c
> > +++ b/fs/proc/base.c
> > @@ -3549,11 +3549,11 @@ static int proc_task_readdir(struct file *file,
> > struct dir_context *ctx)
> > for (task = first_tid(proc_pid(inode), tid, ctx->pos - 2, ns);
> > task;
> > task = next_tid(task), ctx->pos++) {
> > - char name[10 + 1];
> > - unsigned int len;
> > + char name[10], *p = name + sizeof(name);
> > +
>
> Multiple issues:
>
> - len should be 11, as was in the original code
> (0x = 4294967295, 10 letters)
len should be 10.
> - while we're at it, let's use a constant for the '11' instead of
> mysterious magic numbers
>
> - 'p' is clearly overflowing the stack here
>
> > tid = task_pid_nr_ns(task, ns);
> > - len = snprintf(name, sizeof(name), "%u", tid);
> > - if (!proc_fill_cache(file, ctx, name, len,
> > + p = _print_integer_u32(p, tid);
> > + if (!proc_fill_cache(file, ctx, p, name + sizeof(name) - p,
>
> You're replacing snprintf() code __that did proper len checking__
> with code that does not. That's not good.
Yes, the whole point of the patch is to skip length checking.
> I can't see how the fourth proc_fill_cache() parameter, ``name +
> sizeof(name)'' safely ever replace the original 'len' parameter.
> It's a pointer value .. (!)
>
> Overall this looks like a broken patch submitted by mistake.
Re: [PATCH 11/13] proc: readdir /proc/*/task
On Tue, Aug 28, 2018 at 12:36:22PM +, Ahmed S. Darwish wrote:
> On Tue, Aug 28, 2018 at 02:15:01AM +0300, Alexey Dobriyan wrote:
> > ---
> > fs/proc/base.c | 8
> > 1 file changed, 4 insertions(+), 4 deletions(-)
> >
>
> Missing description and S-o-b. Further comments below..
>
> > diff --git a/fs/proc/base.c b/fs/proc/base.c
> > index 33f444721965..668e465c86b3 100644
> > --- a/fs/proc/base.c
> > +++ b/fs/proc/base.c
> > @@ -3549,11 +3549,11 @@ static int proc_task_readdir(struct file *file,
> > struct dir_context *ctx)
> > for (task = first_tid(proc_pid(inode), tid, ctx->pos - 2, ns);
> > task;
> > task = next_tid(task), ctx->pos++) {
> > - char name[10 + 1];
> > - unsigned int len;
> > + char name[10], *p = name + sizeof(name);
> > +
>
> Multiple issues:
>
> - len should be 11, as was in the original code
> (0x = 4294967295, 10 letters)
len should be 10.
> - while we're at it, let's use a constant for the '11' instead of
> mysterious magic numbers
>
> - 'p' is clearly overflowing the stack here
>
> > tid = task_pid_nr_ns(task, ns);
> > - len = snprintf(name, sizeof(name), "%u", tid);
> > - if (!proc_fill_cache(file, ctx, name, len,
> > + p = _print_integer_u32(p, tid);
> > + if (!proc_fill_cache(file, ctx, p, name + sizeof(name) - p,
>
> You're replacing snprintf() code __that did proper len checking__
> with code that does not. That's not good.
Yes, the whole point of the patch is to skip length checking.
> I can't see how the fourth proc_fill_cache() parameter, ``name +
> sizeof(name)'' safely ever replace the original 'len' parameter.
> It's a pointer value .. (!)
>
> Overall this looks like a broken patch submitted by mistake.
Re: [PATCH 11/13] proc: readdir /proc/*/task
On Tue, Aug 28, 2018 at 12:36:22PM +, Ahmed S. Darwish wrote:
> On Tue, Aug 28, 2018 at 02:15:01AM +0300, Alexey Dobriyan wrote:
> > ---
> > fs/proc/base.c | 8
> > 1 file changed, 4 insertions(+), 4 deletions(-)
> >
>
> Missing description and S-o-b. Further comments below..
>
> > diff --git a/fs/proc/base.c b/fs/proc/base.c
> > index 33f444721965..668e465c86b3 100644
> > --- a/fs/proc/base.c
> > +++ b/fs/proc/base.c
> > @@ -3549,11 +3549,11 @@ static int proc_task_readdir(struct file *file,
> > struct dir_context *ctx)
> > for (task = first_tid(proc_pid(inode), tid, ctx->pos - 2, ns);
> > task;
> > task = next_tid(task), ctx->pos++) {
> > - char name[10 + 1];
> > - unsigned int len;
> > + char name[10], *p = name + sizeof(name);
> > +
>
> Multiple issues:
>
> - len should be 11, as was in the original code
> (0x = 4294967295, 10 letters)
>
> - while we're at it, let's use a constant for the '11' instead of
> mysterious magic numbers
>
> - 'p' is clearly overflowing the stack here
>
See below:
> > tid = task_pid_nr_ns(task, ns);
> > - len = snprintf(name, sizeof(name), "%u", tid);
> > - if (!proc_fill_cache(file, ctx, name, len,
> > + p = _print_integer_u32(p, tid);
> > + if (!proc_fill_cache(file, ctx, p, name + sizeof(name) - p,
>
> You're replacing snprintf() code __that did proper len checking__
> with code that does not. That's not good.
>
> I can't see how the fourth proc_fill_cache() parameter, ``name +
> sizeof(name)'' safely ever replace the original 'len' parameter.
> It's a pointer value .. (!)
>
Ok, there's a "- p" in the end, so the length looks to be Ok.
Nonetheless, the whole patch series is introducing funny code
like:
+/*
+ * Print an integer in decimal.
+ * "p" initially points PAST THE END OF THE BUFFER!
+ *
+ * DO NOT USE THESE FUNCTIONS!
+ *
+ * Do not copy these functions.
+ * Do not document these functions.
+ * Do not move these functions to lib/ or elsewhere.
+ * Do not export these functions to modules.
+ * Do not tell anyone about these functions.
+ */
+noinline
+char *_print_integer_u32(char *p, u32 x)
+{
+ do {
+ *--p = '0' + (x % 10);
+ x /= 10;
+ } while (x != 0);
+ return p;
+}
And thus the code using these functions is throwing invalid
past-the-stack pointers and strings with no NULL terminators
like there's no tomorrow...
IMHO It's an accident waiting to happen to sprinkle pointers
like that everywhere. Are we really in a super hot path to
justify all that?
/me confused
--
Darwish
http://darwish.chasingpointers.com
Re: [PATCH 11/13] proc: readdir /proc/*/task
On Tue, Aug 28, 2018 at 12:36:22PM +, Ahmed S. Darwish wrote:
> On Tue, Aug 28, 2018 at 02:15:01AM +0300, Alexey Dobriyan wrote:
> > ---
> > fs/proc/base.c | 8
> > 1 file changed, 4 insertions(+), 4 deletions(-)
> >
>
> Missing description and S-o-b. Further comments below..
>
> > diff --git a/fs/proc/base.c b/fs/proc/base.c
> > index 33f444721965..668e465c86b3 100644
> > --- a/fs/proc/base.c
> > +++ b/fs/proc/base.c
> > @@ -3549,11 +3549,11 @@ static int proc_task_readdir(struct file *file,
> > struct dir_context *ctx)
> > for (task = first_tid(proc_pid(inode), tid, ctx->pos - 2, ns);
> > task;
> > task = next_tid(task), ctx->pos++) {
> > - char name[10 + 1];
> > - unsigned int len;
> > + char name[10], *p = name + sizeof(name);
> > +
>
> Multiple issues:
>
> - len should be 11, as was in the original code
> (0x = 4294967295, 10 letters)
>
> - while we're at it, let's use a constant for the '11' instead of
> mysterious magic numbers
>
> - 'p' is clearly overflowing the stack here
>
See below:
> > tid = task_pid_nr_ns(task, ns);
> > - len = snprintf(name, sizeof(name), "%u", tid);
> > - if (!proc_fill_cache(file, ctx, name, len,
> > + p = _print_integer_u32(p, tid);
> > + if (!proc_fill_cache(file, ctx, p, name + sizeof(name) - p,
>
> You're replacing snprintf() code __that did proper len checking__
> with code that does not. That's not good.
>
> I can't see how the fourth proc_fill_cache() parameter, ``name +
> sizeof(name)'' safely ever replace the original 'len' parameter.
> It's a pointer value .. (!)
>
Ok, there's a "- p" in the end, so the length looks to be Ok.
Nonetheless, the whole patch series is introducing funny code
like:
+/*
+ * Print an integer in decimal.
+ * "p" initially points PAST THE END OF THE BUFFER!
+ *
+ * DO NOT USE THESE FUNCTIONS!
+ *
+ * Do not copy these functions.
+ * Do not document these functions.
+ * Do not move these functions to lib/ or elsewhere.
+ * Do not export these functions to modules.
+ * Do not tell anyone about these functions.
+ */
+noinline
+char *_print_integer_u32(char *p, u32 x)
+{
+ do {
+ *--p = '0' + (x % 10);
+ x /= 10;
+ } while (x != 0);
+ return p;
+}
And thus the code using these functions is throwing invalid
past-the-stack pointers and strings with no NULL terminators
like there's no tomorrow...
IMHO It's an accident waiting to happen to sprinkle pointers
like that everywhere. Are we really in a super hot path to
justify all that?
/me confused
--
Darwish
http://darwish.chasingpointers.com
Re: [PATCH 11/13] proc: readdir /proc/*/task
On Tue, Aug 28, 2018 at 02:15:01AM +0300, Alexey Dobriyan wrote:
> ---
> fs/proc/base.c | 8
> 1 file changed, 4 insertions(+), 4 deletions(-)
>
Missing description and S-o-b. Further comments below..
> diff --git a/fs/proc/base.c b/fs/proc/base.c
> index 33f444721965..668e465c86b3 100644
> --- a/fs/proc/base.c
> +++ b/fs/proc/base.c
> @@ -3549,11 +3549,11 @@ static int proc_task_readdir(struct file *file,
> struct dir_context *ctx)
> for (task = first_tid(proc_pid(inode), tid, ctx->pos - 2, ns);
>task;
>task = next_tid(task), ctx->pos++) {
> - char name[10 + 1];
> - unsigned int len;
> + char name[10], *p = name + sizeof(name);
> +
Multiple issues:
- len should be 11, as was in the original code
(0x = 4294967295, 10 letters)
- while we're at it, let's use a constant for the '11' instead of
mysterious magic numbers
- 'p' is clearly overflowing the stack here
> tid = task_pid_nr_ns(task, ns);
> - len = snprintf(name, sizeof(name), "%u", tid);
> - if (!proc_fill_cache(file, ctx, name, len,
> + p = _print_integer_u32(p, tid);
> + if (!proc_fill_cache(file, ctx, p, name + sizeof(name) - p,
You're replacing snprintf() code __that did proper len checking__
with code that does not. That's not good.
I can't see how the fourth proc_fill_cache() parameter, ``name +
sizeof(name)'' safely ever replace the original 'len' parameter.
It's a pointer value .. (!)
Overall this looks like a broken patch submitted by mistake.
Thanks,
--
Darwish
http://darwish.chasingpointers.com
Re: [PATCH 11/13] proc: readdir /proc/*/task
On Tue, Aug 28, 2018 at 02:15:01AM +0300, Alexey Dobriyan wrote:
> ---
> fs/proc/base.c | 8
> 1 file changed, 4 insertions(+), 4 deletions(-)
>
Missing description and S-o-b. Further comments below..
> diff --git a/fs/proc/base.c b/fs/proc/base.c
> index 33f444721965..668e465c86b3 100644
> --- a/fs/proc/base.c
> +++ b/fs/proc/base.c
> @@ -3549,11 +3549,11 @@ static int proc_task_readdir(struct file *file,
> struct dir_context *ctx)
> for (task = first_tid(proc_pid(inode), tid, ctx->pos - 2, ns);
>task;
>task = next_tid(task), ctx->pos++) {
> - char name[10 + 1];
> - unsigned int len;
> + char name[10], *p = name + sizeof(name);
> +
Multiple issues:
- len should be 11, as was in the original code
(0x = 4294967295, 10 letters)
- while we're at it, let's use a constant for the '11' instead of
mysterious magic numbers
- 'p' is clearly overflowing the stack here
> tid = task_pid_nr_ns(task, ns);
> - len = snprintf(name, sizeof(name), "%u", tid);
> - if (!proc_fill_cache(file, ctx, name, len,
> + p = _print_integer_u32(p, tid);
> + if (!proc_fill_cache(file, ctx, p, name + sizeof(name) - p,
You're replacing snprintf() code __that did proper len checking__
with code that does not. That's not good.
I can't see how the fourth proc_fill_cache() parameter, ``name +
sizeof(name)'' safely ever replace the original 'len' parameter.
It's a pointer value .. (!)
Overall this looks like a broken patch submitted by mistake.
Thanks,
--
Darwish
http://darwish.chasingpointers.com
