path: root/arch/s390/include
diff options
authorHeiko Carstens <heiko.carstens@de.ibm.com>2019-11-18 09:38:37 +0100
committerVasily Gorbik <gor@linux.ibm.com>2019-11-30 10:52:44 +0100
commit5a5525b0488ce31e19065f8527dbf50266b5b712 (patch)
tree962f0b570a299c36ea29f9dd2cb14943b488ca68 /arch/s390/include
parenta2308c11ecbc3471ebb7435ee8075815b1502ef0 (diff)
s390/vdso: fix getcpu
getcpu reads the required values for cpu and node with two instructions. This might lead to an inconsistent result if user space gets preempted and migrated to a different CPU between the two instructions. Fix this by using just a single instruction to read both values at once. This is currently rather a theoretical bug, since there is no real NUMA support available (except for NUMA emulation). Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com> Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com> Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Diffstat (limited to 'arch/s390/include')
1 files changed, 11 insertions, 2 deletions
diff --git a/arch/s390/include/asm/vdso.h b/arch/s390/include/asm/vdso.h
index 169d7604eb80..3bcfdeb01395 100644
--- a/arch/s390/include/asm/vdso.h
+++ b/arch/s390/include/asm/vdso.h
@@ -41,8 +41,17 @@ struct vdso_data {
struct vdso_per_cpu_data {
__u64 ectg_timer_base;
__u64 ectg_user_time;
- __u32 cpu_nr;
- __u32 node_id;
+ /*
+ * Note: node_id and cpu_nr must be at adjacent memory locations.
+ * VDSO userspace must read both values with a single instruction.
+ */
+ union {
+ __u64 getcpu_val;
+ struct {
+ __u32 node_id;
+ __u32 cpu_nr;
+ };
+ };
extern struct vdso_data *vdso_data;

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