On Fri, Jul 15, 2022 at 09:49:24AM -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. > > For cpulist the maximum size is on the order of > NR_CPUS * (ceil(log10(NR_CPUS)) + 1)/2 > > which for 8192 is 20480 (8192 * 5)/2. In order to get near that you'd need > a system with every other CPU on one node. For example: (0,2,4,8, ... ). > To simplify the math and support larger NR_CPUS in the future we are using > (NR_CPUS * 7)/2. We also set it to a min of PAGE_SIZE to retain the older > behavior for smaller NR_CPUS. > > The cpumap file the size works out to be NR_CPUS/4 + NR_CPUS/32 - 1 > (or NR_CPUS * 9/32 - 1) including the ","s. > > Add a set of macros for these values to cpumask.h so they can be used in > multiple places. Apply these to the handful of such files in > drivers/base/topology.c as well as node.c. > > As an example, on an 80 cpu 4-node system (NR_CPUS == 8192): > > before: > > -r--r--r--. 1 root root 0 Jul 12 14:08 system/node/node0/cpulist > -r--r--r--. 1 root root 0 Jul 11 17:25 system/node/node0/cpumap > > after: > > -r--r--r--. 1 root root 28672 Jul 13 11:32 system/node/node0/cpulist > -r--r--r--. 1 root root 4096 Jul 13 11:31 system/node/node0/cpumap > > CONFIG_NR_CPUS = 16384 > -r--r--r--. 1 root root 57344 Jul 13 14:03 system/node/node0/cpulist > -r--r--r--. 1 root root 4607 Jul 13 14:02 system/node/node0/cpumap > > The actual number of cpus doesn't matter for the reported size since they > are based on NR_CPUS. > > Fixes: 75bd50fa841 ("drivers/base/node.c: use bin_attribute to break the size limitation of cpumap ABI") > Fixes: bb9ec13d156 ("topology: use bin_attribute to break the size limitation of cpumap ABI") > Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> > Cc: "Rafael J. Wysocki" <rafael@xxxxxxxxxx> > Cc: Yury Norov <yury.norov@xxxxxxxxx> > Cc: stable@xxxxxxxxxxxxxxx > Signed-off-by: Phil Auld <pauld@xxxxxxxxxx> Acked-by: Yury Norov <yury.norov@xxxxxxxxx> (for include/linux/cpumask.h) > --- > v2: Fix cpumap size calculation. Increase multiplier for cpulist size. > > v3: Add comments in code. > > v4: Define constants in cpumask.h. Move comments there. Also fix > topology.c. > > v5: Fixed math based on Yury's corrections. > > drivers/base/node.c | 4 ++-- > drivers/base/topology.c | 32 ++++++++++++++++---------------- > include/linux/cpumask.h | 18 ++++++++++++++++++ > 3 files changed, 36 insertions(+), 18 deletions(-) > > diff --git a/drivers/base/node.c b/drivers/base/node.c > index 0ac6376ef7a1..eb0f43784c2b 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, CPUMAP_FILE_MAX_BYTES); > > 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, CPULIST_FILE_MAX_BYTES); > > /** > * struct node_access_nodes - Access class device to hold user visible > diff --git a/drivers/base/topology.c b/drivers/base/topology.c > index ac6ad9ab67f9..89f98be5c5b9 100644 > --- a/drivers/base/topology.c > +++ b/drivers/base/topology.c > @@ -62,47 +62,47 @@ define_id_show_func(ppin, "0x%llx"); > static DEVICE_ATTR_ADMIN_RO(ppin); > > define_siblings_read_func(thread_siblings, sibling_cpumask); > -static BIN_ATTR_RO(thread_siblings, 0); > -static BIN_ATTR_RO(thread_siblings_list, 0); > +static BIN_ATTR_RO(thread_siblings, CPUMAP_FILE_MAX_BYTES); > +static BIN_ATTR_RO(thread_siblings_list, CPULIST_FILE_MAX_BYTES); > > define_siblings_read_func(core_cpus, sibling_cpumask); > -static BIN_ATTR_RO(core_cpus, 0); > -static BIN_ATTR_RO(core_cpus_list, 0); > +static BIN_ATTR_RO(core_cpus, CPUMAP_FILE_MAX_BYTES); > +static BIN_ATTR_RO(core_cpus_list, CPULIST_FILE_MAX_BYTES); > > define_siblings_read_func(core_siblings, core_cpumask); > -static BIN_ATTR_RO(core_siblings, 0); > -static BIN_ATTR_RO(core_siblings_list, 0); > +static BIN_ATTR_RO(core_siblings, CPUMAP_FILE_MAX_BYTES); > +static BIN_ATTR_RO(core_siblings_list, CPULIST_FILE_MAX_BYTES); > > #ifdef TOPOLOGY_CLUSTER_SYSFS > define_siblings_read_func(cluster_cpus, cluster_cpumask); > -static BIN_ATTR_RO(cluster_cpus, 0); > -static BIN_ATTR_RO(cluster_cpus_list, 0); > +static BIN_ATTR_RO(cluster_cpus, CPUMAP_FILE_MAX_BYTES); > +static BIN_ATTR_RO(cluster_cpus_list, CPULIST_FILE_MAX_BYTES); > #endif > > #ifdef TOPOLOGY_DIE_SYSFS > define_siblings_read_func(die_cpus, die_cpumask); > -static BIN_ATTR_RO(die_cpus, 0); > -static BIN_ATTR_RO(die_cpus_list, 0); > +static BIN_ATTR_RO(die_cpus, CPUMAP_FILE_MAX_BYTES); > +static BIN_ATTR_RO(die_cpus_list, CPULIST_FILE_MAX_BYTES); > #endif > > define_siblings_read_func(package_cpus, core_cpumask); > -static BIN_ATTR_RO(package_cpus, 0); > -static BIN_ATTR_RO(package_cpus_list, 0); > +static BIN_ATTR_RO(package_cpus, CPUMAP_FILE_MAX_BYTES); > +static BIN_ATTR_RO(package_cpus_list, CPULIST_FILE_MAX_BYTES); > > #ifdef TOPOLOGY_BOOK_SYSFS > define_id_show_func(book_id, "%d"); > static DEVICE_ATTR_RO(book_id); > define_siblings_read_func(book_siblings, book_cpumask); > -static BIN_ATTR_RO(book_siblings, 0); > -static BIN_ATTR_RO(book_siblings_list, 0); > +static BIN_ATTR_RO(book_siblings, CPUMAP_FILE_MAX_BYTES); > +static BIN_ATTR_RO(book_siblings_list, CPULIST_FILE_MAX_BYTES); > #endif > > #ifdef TOPOLOGY_DRAWER_SYSFS > define_id_show_func(drawer_id, "%d"); > static DEVICE_ATTR_RO(drawer_id); > define_siblings_read_func(drawer_siblings, drawer_cpumask); > -static BIN_ATTR_RO(drawer_siblings, 0); > -static BIN_ATTR_RO(drawer_siblings_list, 0); > +static BIN_ATTR_RO(drawer_siblings, CPUMAP_FILE_MAX_BYTES); > +static BIN_ATTR_RO(drawer_siblings_list, CPULIST_FILE_MAX_BYTES); > #endif > > static struct bin_attribute *bin_attrs[] = { > diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h > index fe29ac7cc469..4592d0845941 100644 > --- a/include/linux/cpumask.h > +++ b/include/linux/cpumask.h > @@ -1071,4 +1071,22 @@ cpumap_print_list_to_buf(char *buf, const struct cpumask *mask, > [0] = 1UL \ > } } > > +/* > + * Provide a valid theoretical max size for cpumap and cpulist sysfs files > + * to avoid breaking userspace which may allocate a buffer based on the size > + * reported by e.g. fstat. > + * > + * for cpumap NR_CPUS * 9/32 - 1 should be an exact length. > + * > + * For cpulist 7 is (ceil(log10(NR_CPUS)) + 1) allowing for NR_CPUS to be up > + * to 2 orders of magnitude larger than 8192. And then we divide by 2 to > + * cover a worst-case of every other cpu being on one of two nodes for a > + * very large NR_CPUS. > + * > + * Use PAGE_SIZE as a minimum for smaller configurations. > + */ > +#define CPUMAP_FILE_MAX_BYTES ((((NR_CPUS * 9)/32 - 1) > PAGE_SIZE) \ > + ? (NR_CPUS * 9)/32 - 1 : PAGE_SIZE) > +#define CPULIST_FILE_MAX_BYTES (((NR_CPUS * 7)/2 > PAGE_SIZE) ? (NR_CPUS * 7)/2 : PAGE_SIZE) > + > #endif /* __LINUX_CPUMASK_H */ > -- > 2.31.1