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SubjectRe: [PATCH] mm: might_sleep warning
On Tue, 6 Mar 2018 15:48:26 -0500 Pavel Tatashin <pasha.tatashin@oracle.com> wrote:

> On Tue, Mar 6, 2018 at 3:36 PM, Andrew Morton <akpm@linux-foundation.org>
> wrote:
>
> > On Tue, 6 Mar 2018 14:20:22 -0500 Pavel Tatashin <
> > pasha.tatashin@oracle.com> wrote:
> >
> > > spin_lock(&deferred_zone_grow_lock);
> > > - static_branch_disable(&deferred_pages);
> > > + deferred_zone_grow = false;
> > > spin_unlock(&deferred_zone_grow_lock);
> > > + static_branch_disable(&deferred_pages);
> > >
> > > /* There will be num_node_state(N_MEMORY) threads */
> > > atomic_set(&pgdat_init_n_undone, num_node_state(N_MEMORY));
> >
> > Kinda ugly, but I can see the logic behind the decisions.
> >
> > Can we instead turn deferred_zone_grow_lock into a mutex?

(top-posting repaired. Please don't top-post).

> [CCed everyone]
>
> Hi Andrew,
>
> I afraid we cannot change this spinlock to mutex
> because deferred_grow_zone() might be called from an interrupt context if
> interrupt thread needs to allocate memory.
>

OK. But if deferred_grow_zone() can be called from interrupt then
page_alloc_init_late() should be using spin_lock_irq(), shouldn't it?
I'm surprised that lockdep didn't detect that.


--- a/mm/page_alloc.c~mm-initialize-pages-on-demand-during-boot-fix-4-fix
+++ a/mm/page_alloc.c
@@ -1689,9 +1689,9 @@ void __init page_alloc_init_late(void)
* context. Since, spin_lock() disables preemption, we must use an
* extra boolean deferred_zone_grow.
*/
- spin_lock(&deferred_zone_grow_lock);
+ spin_lock_irq(&deferred_zone_grow_lock);
deferred_zone_grow = false;
- spin_unlock(&deferred_zone_grow_lock);
+ spin_unlock_irq(&deferred_zone_grow_lock);
static_branch_disable(&deferred_pages);

/* There will be num_node_state(N_MEMORY) threads */
_
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