Subject: linux-next: build failure after merge of the bpf-next tree

From: Stephen Rothwell <[email-masked]>
Date: Wed, 19 Mar 2025 13:33:09 +1100

Hi all,

After merging the bpf-next tree, today's linux-next build (x86_64
allmodconfig) failed like this:

In file included from include/asm-generic/percpu.h:7,
                 from arch/x86/include/asm/percpu.h:630,
                 from arch/x86/include/asm/preempt.h:6,
                 from include/linux/preempt.h:79,
                 from include/linux/smp.h:116,
                 from kernel/locking/qspinlock.c:16:
kernel/locking/qspinlock.h: In function 'decode_tail':
include/linux/percpu-defs.h:219:45: error: initialization from pointer to non-enclosed address space
  219 |         const void __percpu *__vpp_verify = (typeof((ptr) + 0))NULL;    \
      |                                             ^
include/linux/percpu-defs.h:237:9: note: in expansion of macro '__verify_pcpu_ptr'
  237 |         __verify_pcpu_ptr(ptr);                                         \
      |         ^~~~~~~~~~~~~~~~~
kernel/locking/qspinlock.h:67:16: note: in expansion of macro 'per_cpu_ptr'
   67 |         return per_cpu_ptr(&qnodes[idx].mcs, cpu);
      |                ^~~~~~~~~~~
include/linux/percpu-defs.h:219:45: note: expected 'const __seg_gs void *' but pointer is of type 'struct mcs_spinlock *'
  219 |         const void __percpu *__vpp_verify = (typeof((ptr) + 0))NULL;    \
      |                                             ^
include/linux/percpu-defs.h:237:9: note: in expansion of macro '__verify_pcpu_ptr'
  237 |         __verify_pcpu_ptr(ptr);                                         \
      |         ^~~~~~~~~~~~~~~~~
kernel/locking/qspinlock.h:67:16: note: in expansion of macro 'per_cpu_ptr'
   67 |         return per_cpu_ptr(&qnodes[idx].mcs, cpu);
      |                ^~~~~~~~~~~
kernel/locking/qspinlock.c: In function 'native_queued_spin_lock_slowpath':
kernel/locking/qspinlock.c:285:41: error: passing argument 2 of 'decode_tail' from pointer to non-enclosed address space
  285 |                 prev = decode_tail(old, qnodes);
      |                                         ^~~~~~
In file included from kernel/locking/qspinlock.c:30:
kernel/locking/qspinlock.h:62:79: note: expected 'struct qnode *' but argument is of type '__seg_gs struct qnode *'
   62 | static inline __pure struct mcs_spinlock *decode_tail(u32 tail, struct qnode *qnodes)
      |                                                                 ~~~~~~~~~~~~~~^~~~~~
In file included from kernel/locking/qspinlock.c:401:
kernel/locking/qspinlock.c: In function '__pv_queued_spin_lock_slowpath':
kernel/locking/qspinlock.c:285:41: error: passing argument 2 of 'decode_tail' from pointer to non-enclosed address space
  285 |                 prev = decode_tail(old, qnodes);
      |                                         ^~~~~~
kernel/locking/qspinlock.h:62:79: note: expected 'struct qnode *' but argument is of type '__seg_gs struct qnode *'
   62 | static inline __pure struct mcs_spinlock *decode_tail(u32 tail, struct qnode *qnodes)
      |                                                                 ~~~~~~~~~~~~~~^~~~~~

Caused by the resilient-queued-spin-lock branch of the bpf-next tree
interacting with the "Enable strict percpu address space checks" series
form the mm-stable tree.

I don't know why this happens, but reverting that branch inf the bpf-next
tree makes the failure go away, so I have done that for today.

-- 
Cheers,
Stephen Rothwell