From: Phil Auld pauld@redhat.com
commit 7ee951acd31a88f941fd6535fbdee3a1567f1d63 upstream.
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: 75bd50fa841d ("drivers/base/node.c: use bin_attribute to break the size limitation of cpumap ABI") Fixes: bb9ec13d156e ("topology: 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 Cc: Yury Norov yury.norov@gmail.com Cc: stable@vger.kernel.org Acked-by: Yury Norov yury.norov@gmail.com (for include/linux/cpumask.h) Signed-off-by: Phil Auld pauld@redhat.com Link: https://lore.kernel.org/r/20220715134924.3466194-1-pauld@redhat.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/base/node.c | 4 ++-- drivers/base/topology.c | 32 ++++++++++++++++---------------- include/linux/cpumask.h | 18 ++++++++++++++++++ 3 files changed, 36 insertions(+), 18 deletions(-)
--- a/drivers/base/node.c +++ b/drivers/base/node.c @@ -45,7 +45,7 @@ static inline ssize_t cpumap_read(struct 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(struc 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 --- 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[] = { --- a/include/linux/cpumask.h +++ b/include/linux/cpumask.h @@ -1071,4 +1071,22 @@ cpumap_print_list_to_buf(char *buf, cons [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 */