* [PATCH v2] drivers/base/node.c: fix userspace break from using bin_attributes for cpumap and cpulist
@ 2022-07-13 13:45 Phil Auld
2022-07-13 13:58 ` Greg Kroah-Hartman
0 siblings, 1 reply; 5+ messages in thread
From: Phil Auld @ 2022-07-13 13:45 UTC (permalink / raw)
To: linux-kernel; +Cc: Greg Kroah-Hartman, Rafael J . Wysocki, Barry Song, Tian Tao
Using bin_attributes with a 0 size causes fstat and friends to return that 0 size.
This breaks userspace code that retrieves the size before reading the file. Rather
than reverting 75bd50fa841 ("drivers/base/node.c: use bin_attribute to break the size
limitation of cpumap ABI") let's put in a size value at compile time. Use direct
comparison and a worst-case maximum to ensure compile time constants. For cpulist the
max is on the order of NR_CPUS * (ceil(log10(NR_CPUS)) + 1) which for 8192 is 40960
(8192 * 5). In order to get near that you'd need a system with every other CPU on one
node or something similar. e.g. (0,2,4,... 1024,1026...). To simplify the math and
support larger NR_CPUS we are using NR_CPUS * 6. We also set it to a min of PAGE_SIZE
to retain the older behavior for smaller NR_CPUS. The cpumap file wants to be something
like NR_CPUS/4 + NR_CPUS/32, for the ","s so for simplicity we are using NR_CPUS/2.
On an 80 cpu 4-node sytem (NR_CPUS == 8192)
before:
-r--r--r--. 1 root root 0 Jul 12 14:08 /sys/devices/system/node/node0/cpulist
-r--r--r--. 1 root root 0 Jul 11 17:25 /sys/devices/system/node/node0/cpumap
after:
-r--r--r--. 1 root root 49152 Jul 13 09:26 /sys/devices/system/node/node0/cpulist
-r--r--r--. 1 root root 4096 Jul 13 09:24 /sys/devices/system/node/node0/cpumap
Fixes: 75bd50fa841 ("drivers/base/node.c: use bin_attribute to break the size limitation of cpumap ABI")
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: "Rafael J. Wysocki" <rafael@kernel.org>
Signed-off-by: Phil Auld <pauld@redhat.com>
---
drivers/base/node.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/drivers/base/node.c b/drivers/base/node.c
index 0ac6376ef7a1..3577f4eb4ac6 100644
--- a/drivers/base/node.c
+++ b/drivers/base/node.c
@@ -45,7 +45,7 @@ static inline ssize_t cpumap_read(struct file *file, struct kobject *kobj,
return n;
}
-static BIN_ATTR_RO(cpumap, 0);
+static BIN_ATTR_RO(cpumap, (((NR_CPUS>>1) > PAGE_SIZE) ? NR_CPUS >> 1 : PAGE_SIZE));
static inline ssize_t cpulist_read(struct file *file, struct kobject *kobj,
struct bin_attribute *attr, char *buf,
@@ -66,7 +66,7 @@ static inline ssize_t cpulist_read(struct file *file, struct kobject *kobj,
return n;
}
-static BIN_ATTR_RO(cpulist, 0);
+static BIN_ATTR_RO(cpulist, (((NR_CPUS * 6) > PAGE_SIZE) ? NR_CPUS *6 : PAGE_SIZE));
/**
* struct node_access_nodes - Access class device to hold user visible
--
2.31.1
^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [PATCH v2] drivers/base/node.c: fix userspace break from using bin_attributes for cpumap and cpulist
2022-07-13 13:45 [PATCH v2] drivers/base/node.c: fix userspace break from using bin_attributes for cpumap and cpulist Phil Auld
@ 2022-07-13 13:58 ` Greg Kroah-Hartman
2022-07-13 14:13 ` Phil Auld
0 siblings, 1 reply; 5+ messages in thread
From: Greg Kroah-Hartman @ 2022-07-13 13:58 UTC (permalink / raw)
To: Phil Auld; +Cc: linux-kernel, Rafael J . Wysocki, Barry Song, Tian Tao
On Wed, Jul 13, 2022 at 09:45:45AM -0400, Phil Auld wrote:
> Using bin_attributes with a 0 size causes fstat and friends to return that 0 size.
> This breaks userspace code that retrieves the size before reading the file. Rather
> than reverting 75bd50fa841 ("drivers/base/node.c: use bin_attribute to break the size
> limitation of cpumap ABI") let's put in a size value at compile time. Use direct
> comparison and a worst-case maximum to ensure compile time constants. For cpulist the
> max is on the order of NR_CPUS * (ceil(log10(NR_CPUS)) + 1) which for 8192 is 40960
> (8192 * 5). In order to get near that you'd need a system with every other CPU on one
> node or something similar. e.g. (0,2,4,... 1024,1026...). To simplify the math and
> support larger NR_CPUS we are using NR_CPUS * 6. We also set it to a min of PAGE_SIZE
> to retain the older behavior for smaller NR_CPUS. The cpumap file wants to be something
> like NR_CPUS/4 + NR_CPUS/32, for the ","s so for simplicity we are using NR_CPUS/2.
>
> On an 80 cpu 4-node sytem (NR_CPUS == 8192)
>
> before:
>
> -r--r--r--. 1 root root 0 Jul 12 14:08 /sys/devices/system/node/node0/cpulist
> -r--r--r--. 1 root root 0 Jul 11 17:25 /sys/devices/system/node/node0/cpumap
>
> after:
>
> -r--r--r--. 1 root root 49152 Jul 13 09:26 /sys/devices/system/node/node0/cpulist
> -r--r--r--. 1 root root 4096 Jul 13 09:24 /sys/devices/system/node/node0/cpumap
>
> Fixes: 75bd50fa841 ("drivers/base/node.c: use bin_attribute to break the size limitation of cpumap ABI")
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Cc: "Rafael J. Wysocki" <rafael@kernel.org>
> Signed-off-by: Phil Auld <pauld@redhat.com>
> ---
> drivers/base/node.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/base/node.c b/drivers/base/node.c
> index 0ac6376ef7a1..3577f4eb4ac6 100644
> --- a/drivers/base/node.c
> +++ b/drivers/base/node.c
> @@ -45,7 +45,7 @@ static inline ssize_t cpumap_read(struct file *file, struct kobject *kobj,
> return n;
> }
>
> -static BIN_ATTR_RO(cpumap, 0);
> +static BIN_ATTR_RO(cpumap, (((NR_CPUS>>1) > PAGE_SIZE) ? NR_CPUS >> 1 : PAGE_SIZE));
Why not just PAGE_SIZE?
If not, a HUGE comment explaining what you are doing here is going to be
required.
>
> static inline ssize_t cpulist_read(struct file *file, struct kobject *kobj,
> struct bin_attribute *attr, char *buf,
> @@ -66,7 +66,7 @@ static inline ssize_t cpulist_read(struct file *file, struct kobject *kobj,
> return n;
> }
>
> -static BIN_ATTR_RO(cpulist, 0);
> +static BIN_ATTR_RO(cpulist, (((NR_CPUS * 6) > PAGE_SIZE) ? NR_CPUS *6 : PAGE_SIZE));
"* 6" in both places here?
And again, we need a huge comment explaining this so that we can
understand it in a few weeks, and in 10 years...
thanks,
greg k-h
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH v2] drivers/base/node.c: fix userspace break from using bin_attributes for cpumap and cpulist
2022-07-13 13:58 ` Greg Kroah-Hartman
@ 2022-07-13 14:13 ` Phil Auld
2022-07-13 14:25 ` Greg Kroah-Hartman
0 siblings, 1 reply; 5+ messages in thread
From: Phil Auld @ 2022-07-13 14:13 UTC (permalink / raw)
To: Greg Kroah-Hartman; +Cc: linux-kernel, Rafael J . Wysocki, Barry Song, Tian Tao
On Wed, Jul 13, 2022 at 03:58:43PM +0200 Greg Kroah-Hartman wrote:
> On Wed, Jul 13, 2022 at 09:45:45AM -0400, Phil Auld wrote:
> > Using bin_attributes with a 0 size causes fstat and friends to return that 0 size.
> > This breaks userspace code that retrieves the size before reading the file. Rather
> > than reverting 75bd50fa841 ("drivers/base/node.c: use bin_attribute to break the size
> > limitation of cpumap ABI") let's put in a size value at compile time. Use direct
> > comparison and a worst-case maximum to ensure compile time constants. For cpulist the
> > max is on the order of NR_CPUS * (ceil(log10(NR_CPUS)) + 1) which for 8192 is 40960
> > (8192 * 5). In order to get near that you'd need a system with every other CPU on one
> > node or something similar. e.g. (0,2,4,... 1024,1026...). To simplify the math and
> > support larger NR_CPUS we are using NR_CPUS * 6. We also set it to a min of PAGE_SIZE
> > to retain the older behavior for smaller NR_CPUS. The cpumap file wants to be something
> > like NR_CPUS/4 + NR_CPUS/32, for the ","s so for simplicity we are using NR_CPUS/2.
> >
> > On an 80 cpu 4-node sytem (NR_CPUS == 8192)
> >
> > before:
> >
> > -r--r--r--. 1 root root 0 Jul 12 14:08 /sys/devices/system/node/node0/cpulist
> > -r--r--r--. 1 root root 0 Jul 11 17:25 /sys/devices/system/node/node0/cpumap
> >
> > after:
> >
> > -r--r--r--. 1 root root 49152 Jul 13 09:26 /sys/devices/system/node/node0/cpulist
> > -r--r--r--. 1 root root 4096 Jul 13 09:24 /sys/devices/system/node/node0/cpumap
> >
> > Fixes: 75bd50fa841 ("drivers/base/node.c: use bin_attribute to break the size limitation of cpumap ABI")
> > Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> > Cc: "Rafael J. Wysocki" <rafael@kernel.org>
> > Signed-off-by: Phil Auld <pauld@redhat.com>
> > ---
> > drivers/base/node.c | 4 ++--
> > 1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/base/node.c b/drivers/base/node.c
> > index 0ac6376ef7a1..3577f4eb4ac6 100644
> > --- a/drivers/base/node.c
> > +++ b/drivers/base/node.c
> > @@ -45,7 +45,7 @@ static inline ssize_t cpumap_read(struct file *file, struct kobject *kobj,
> > return n;
> > }
> >
> > -static BIN_ATTR_RO(cpumap, 0);
> > +static BIN_ATTR_RO(cpumap, (((NR_CPUS>>1) > PAGE_SIZE) ? NR_CPUS >> 1 : PAGE_SIZE));
>
> Why not just PAGE_SIZE?
>
This one is likely to grow beyond page size if NR_CPUS is larger than 8192. It's about 2300 bytes
at 8192 if my math is right.
Let me ask again before I write the comments... what values of NR_CPUS are you seeing? Are people
using an order of magnitude above 8192? Two orders? This patch (with the 6 below) handles about 1
order more.
> If not, a HUGE comment explaining what you are doing here is going to be
> required.
Sure, will do. See above :)
>
> >
> > static inline ssize_t cpulist_read(struct file *file, struct kobject *kobj,
> > struct bin_attribute *attr, char *buf,
> > @@ -66,7 +66,7 @@ static inline ssize_t cpulist_read(struct file *file, struct kobject *kobj,
> > return n;
> > }
> >
> > -static BIN_ATTR_RO(cpulist, 0);
> > +static BIN_ATTR_RO(cpulist, (((NR_CPUS * 6) > PAGE_SIZE) ? NR_CPUS *6 : PAGE_SIZE));
>
> "* 6" in both places here?
>
It's compile time so it's cheap. But yes, 6 in both places. That's to support NR_CPUS=100000.
> And again, we need a huge comment explaining this so that we can
> understand it in a few weeks, and in 10 years...
Will do.
Thanks,
Phil
>
> thanks,
>
> greg k-h
>
--
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH v2] drivers/base/node.c: fix userspace break from using bin_attributes for cpumap and cpulist
2022-07-13 14:13 ` Phil Auld
@ 2022-07-13 14:25 ` Greg Kroah-Hartman
2022-07-13 14:48 ` Phil Auld
0 siblings, 1 reply; 5+ messages in thread
From: Greg Kroah-Hartman @ 2022-07-13 14:25 UTC (permalink / raw)
To: Phil Auld; +Cc: linux-kernel, Rafael J . Wysocki, Barry Song, Tian Tao
On Wed, Jul 13, 2022 at 10:13:28AM -0400, Phil Auld wrote:
> On Wed, Jul 13, 2022 at 03:58:43PM +0200 Greg Kroah-Hartman wrote:
> > On Wed, Jul 13, 2022 at 09:45:45AM -0400, Phil Auld wrote:
> > > Using bin_attributes with a 0 size causes fstat and friends to return that 0 size.
> > > This breaks userspace code that retrieves the size before reading the file. Rather
> > > than reverting 75bd50fa841 ("drivers/base/node.c: use bin_attribute to break the size
> > > limitation of cpumap ABI") let's put in a size value at compile time. Use direct
> > > comparison and a worst-case maximum to ensure compile time constants. For cpulist the
> > > max is on the order of NR_CPUS * (ceil(log10(NR_CPUS)) + 1) which for 8192 is 40960
> > > (8192 * 5). In order to get near that you'd need a system with every other CPU on one
> > > node or something similar. e.g. (0,2,4,... 1024,1026...). To simplify the math and
> > > support larger NR_CPUS we are using NR_CPUS * 6. We also set it to a min of PAGE_SIZE
> > > to retain the older behavior for smaller NR_CPUS. The cpumap file wants to be something
> > > like NR_CPUS/4 + NR_CPUS/32, for the ","s so for simplicity we are using NR_CPUS/2.
> > >
> > > On an 80 cpu 4-node sytem (NR_CPUS == 8192)
> > >
> > > before:
> > >
> > > -r--r--r--. 1 root root 0 Jul 12 14:08 /sys/devices/system/node/node0/cpulist
> > > -r--r--r--. 1 root root 0 Jul 11 17:25 /sys/devices/system/node/node0/cpumap
> > >
> > > after:
> > >
> > > -r--r--r--. 1 root root 49152 Jul 13 09:26 /sys/devices/system/node/node0/cpulist
> > > -r--r--r--. 1 root root 4096 Jul 13 09:24 /sys/devices/system/node/node0/cpumap
> > >
> > > Fixes: 75bd50fa841 ("drivers/base/node.c: use bin_attribute to break the size limitation of cpumap ABI")
> > > Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> > > Cc: "Rafael J. Wysocki" <rafael@kernel.org>
> > > Signed-off-by: Phil Auld <pauld@redhat.com>
> > > ---
> > > drivers/base/node.c | 4 ++--
> > > 1 file changed, 2 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/drivers/base/node.c b/drivers/base/node.c
> > > index 0ac6376ef7a1..3577f4eb4ac6 100644
> > > --- a/drivers/base/node.c
> > > +++ b/drivers/base/node.c
> > > @@ -45,7 +45,7 @@ static inline ssize_t cpumap_read(struct file *file, struct kobject *kobj,
> > > return n;
> > > }
> > >
> > > -static BIN_ATTR_RO(cpumap, 0);
> > > +static BIN_ATTR_RO(cpumap, (((NR_CPUS>>1) > PAGE_SIZE) ? NR_CPUS >> 1 : PAGE_SIZE));
> >
> > Why not just PAGE_SIZE?
> >
>
> This one is likely to grow beyond page size if NR_CPUS is larger than 8192. It's about 2300 bytes
> at 8192 if my math is right.
>
> Let me ask again before I write the comments... what values of NR_CPUS are you seeing? Are people
> using an order of magnitude above 8192? Two orders? This patch (with the 6 below) handles about 1
> order more.
One order for now that we know of, probably larger that we don't :)
> > > static inline ssize_t cpulist_read(struct file *file, struct kobject *kobj,
> > > struct bin_attribute *attr, char *buf,
> > > @@ -66,7 +66,7 @@ static inline ssize_t cpulist_read(struct file *file, struct kobject *kobj,
> > > return n;
> > > }
> > >
> > > -static BIN_ATTR_RO(cpulist, 0);
> > > +static BIN_ATTR_RO(cpulist, (((NR_CPUS * 6) > PAGE_SIZE) ? NR_CPUS *6 : PAGE_SIZE));
> >
> > "* 6" in both places here?
> >
>
> It's compile time so it's cheap. But yes, 6 in both places. That's to support NR_CPUS=100000.
Sorry, I was trying to point out to use a " " before the "6" in both
places. Not questioning the math.
thanks,
greg k-h
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH v2] drivers/base/node.c: fix userspace break from using bin_attributes for cpumap and cpulist
2022-07-13 14:25 ` Greg Kroah-Hartman
@ 2022-07-13 14:48 ` Phil Auld
0 siblings, 0 replies; 5+ messages in thread
From: Phil Auld @ 2022-07-13 14:48 UTC (permalink / raw)
To: Greg Kroah-Hartman; +Cc: linux-kernel, Rafael J . Wysocki, Barry Song, Tian Tao
On Wed, Jul 13, 2022 at 04:25:30PM +0200 Greg Kroah-Hartman wrote:
> On Wed, Jul 13, 2022 at 10:13:28AM -0400, Phil Auld wrote:
> > On Wed, Jul 13, 2022 at 03:58:43PM +0200 Greg Kroah-Hartman wrote:
> > > On Wed, Jul 13, 2022 at 09:45:45AM -0400, Phil Auld wrote:
> > > > Using bin_attributes with a 0 size causes fstat and friends to return that 0 size.
> > > > This breaks userspace code that retrieves the size before reading the file. Rather
> > > > than reverting 75bd50fa841 ("drivers/base/node.c: use bin_attribute to break the size
> > > > limitation of cpumap ABI") let's put in a size value at compile time. Use direct
> > > > comparison and a worst-case maximum to ensure compile time constants. For cpulist the
> > > > max is on the order of NR_CPUS * (ceil(log10(NR_CPUS)) + 1) which for 8192 is 40960
> > > > (8192 * 5). In order to get near that you'd need a system with every other CPU on one
> > > > node or something similar. e.g. (0,2,4,... 1024,1026...). To simplify the math and
> > > > support larger NR_CPUS we are using NR_CPUS * 6. We also set it to a min of PAGE_SIZE
> > > > to retain the older behavior for smaller NR_CPUS. The cpumap file wants to be something
> > > > like NR_CPUS/4 + NR_CPUS/32, for the ","s so for simplicity we are using NR_CPUS/2.
> > > >
> > > > On an 80 cpu 4-node sytem (NR_CPUS == 8192)
> > > >
> > > > before:
> > > >
> > > > -r--r--r--. 1 root root 0 Jul 12 14:08 /sys/devices/system/node/node0/cpulist
> > > > -r--r--r--. 1 root root 0 Jul 11 17:25 /sys/devices/system/node/node0/cpumap
> > > >
> > > > after:
> > > >
> > > > -r--r--r--. 1 root root 49152 Jul 13 09:26 /sys/devices/system/node/node0/cpulist
> > > > -r--r--r--. 1 root root 4096 Jul 13 09:24 /sys/devices/system/node/node0/cpumap
> > > >
> > > > Fixes: 75bd50fa841 ("drivers/base/node.c: use bin_attribute to break the size limitation of cpumap ABI")
> > > > Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> > > > Cc: "Rafael J. Wysocki" <rafael@kernel.org>
> > > > Signed-off-by: Phil Auld <pauld@redhat.com>
> > > > ---
> > > > drivers/base/node.c | 4 ++--
> > > > 1 file changed, 2 insertions(+), 2 deletions(-)
> > > >
> > > > diff --git a/drivers/base/node.c b/drivers/base/node.c
> > > > index 0ac6376ef7a1..3577f4eb4ac6 100644
> > > > --- a/drivers/base/node.c
> > > > +++ b/drivers/base/node.c
> > > > @@ -45,7 +45,7 @@ static inline ssize_t cpumap_read(struct file *file, struct kobject *kobj,
> > > > return n;
> > > > }
> > > >
> > > > -static BIN_ATTR_RO(cpumap, 0);
> > > > +static BIN_ATTR_RO(cpumap, (((NR_CPUS>>1) > PAGE_SIZE) ? NR_CPUS >> 1 : PAGE_SIZE));
> > >
> > > Why not just PAGE_SIZE?
> > >
> >
> > This one is likely to grow beyond page size if NR_CPUS is larger than 8192. It's about 2300 bytes
> > at 8192 if my math is right.
> >
> > Let me ask again before I write the comments... what values of NR_CPUS are you seeing? Are people
> > using an order of magnitude above 8192? Two orders? This patch (with the 6 below) handles about 1
> > order more.
>
> One order for now that we know of, probably larger that we don't :)
Fair enough. I'll go with 7 then. Thanks!
>
> > > > static inline ssize_t cpulist_read(struct file *file, struct kobject *kobj,
> > > > struct bin_attribute *attr, char *buf,
> > > > @@ -66,7 +66,7 @@ static inline ssize_t cpulist_read(struct file *file, struct kobject *kobj,
> > > > return n;
> > > > }
> > > >
> > > > -static BIN_ATTR_RO(cpulist, 0);
> > > > +static BIN_ATTR_RO(cpulist, (((NR_CPUS * 6) > PAGE_SIZE) ? NR_CPUS *6 : PAGE_SIZE));
> > >
> > > "* 6" in both places here?
> > >
> >
> > It's compile time so it's cheap. But yes, 6 in both places. That's to support NR_CPUS=100000.
>
> Sorry, I was trying to point out to use a " " before the "6" in both
> places. Not questioning the math.
>
Right! Sorry, misunderstood, obviously :)
Cheers,
Phil
> thanks,
>
> greg k-h
>
--
^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2022-07-13 14:48 UTC | newest]
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2022-07-13 13:45 [PATCH v2] drivers/base/node.c: fix userspace break from using bin_attributes for cpumap and cpulist Phil Auld
2022-07-13 13:58 ` Greg Kroah-Hartman
2022-07-13 14:13 ` Phil Auld
2022-07-13 14:25 ` Greg Kroah-Hartman
2022-07-13 14:48 ` Phil Auld
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