MN10300: Fix the PERCPU() alignment to allow for workqueues

In the MN10300 arch, we occasionally see an assertion being tripped in
alloc_cwqs() at the following line:

        /* just in case, make sure it's actually aligned */
  --->  BUG_ON(!IS_ALIGNED(wq->cpu_wq.v, align));
        return wq->cpu_wq.v ? 0 : -ENOMEM;

The values are:

        wa->cpu_wq.v => 0x902776e0
        align => 0x100

and align is calculated by the following:

        const size_t align = max_t(size_t, 1 << WORK_STRUCT_FLAG_BITS,
                                   __alignof__(unsigned long long));

This is because the pointer in question (wq->cpu_wq.v) loses some of its
lower bits to control flags, and so the object it points to must be
sufficiently aligned to avoid the need to use those bits for pointing to
things.

Currently, 4 control bits and 4 colour bits are used in normal
circumstances, plus a debugging bit if debugging is set.  This requires
the cpu_workqueue_struct struct to be at least 256 bytes aligned (or 512
bytes aligned with debugging).

PERCPU() alignment on MN13000, however, is only 32 bytes as set in
vmlinux.lds.S.  So we set this to PAGE_SIZE (4096) to match most other
arches and stick a comment in alloc_cwqs() for anyone else who triggers
the assertion.

Reported-by: Akira Takeuchi <takeuchi.akr@jp.panasonic.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Mark Salter <msalter@redhat.com>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/arch/mn10300/kernel/vmlinux.lds.S b/arch/mn10300/kernel/vmlinux.lds.S
index 10549dcfb610fca868a0e623a367d2ea5be55ed9..febbeee7f2f54ba99bf429b72d9ea74aab80be62 100644 (file)
--- a/arch/mn10300/kernel/vmlinux.lds.S
+++ b/arch/mn10300/kernel/vmlinux.lds.S
@@ -70,7 +70,7 @@ SECTIONS
        .exit.text : { EXIT_TEXT; }
        .exit.data : { EXIT_DATA; }
 
-  PERCPU(32)
+  PERCPU(PAGE_SIZE)
   . = ALIGN(PAGE_SIZE);
   __init_end = .;
   /* freed after init ends here */

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 30acdb74cc23bfb21d1dcc0a14433003c9e085b7..e5ff2cbaadc21d8e138b24c63dda236c4acb0350 100644 (file)
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -2791,7 +2791,9 @@ static int alloc_cwqs(struct workqueue_struct *wq)
                }
        }
 
-       /* just in case, make sure it's actually aligned */
+       /* just in case, make sure it's actually aligned
+        * - this is affected by PERCPU() alignment in vmlinux.lds.S
+        */
        BUG_ON(!IS_ALIGNED(wq->cpu_wq.v, align));
        return wq->cpu_wq.v ? 0 : -ENOMEM;
 }