Messages in this thread Patch in this message | | | From | Phil Auld <> | Subject | [PATCH] drivers/base/node.c: fix userspace break from using bin_attributes for cpumap and cpulist | Date | Tue, 12 Jul 2022 17:43:01 -0400 |
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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. 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...). We set it to a min of PAGE_SIZE to retain the older behavior. For cpumap, PAGE_SIZE is plenty big.
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 40960 Jul 12 16:48 /sys/devices/system/node/node0/cpulist -r--r--r--. 1 root root 4096 Jul 12 15:50 /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..291c69671f23 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, 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 * 5) > PAGE_SIZE) ? NR_CPUS *5 : PAGE_SIZE)); /** * struct node_access_nodes - Access class device to hold user visible -- 2.31.1
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