On Tue, 6 Mar 2018 16:04:06 -0500 Pavel Tatashin <pasha.tatashin@xxxxxxxxxx> 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. > > No, page_alloc_init_late() cannot be called from interrupt, it is > called straight from: > kernel_init_freeable(). But, I believe deferred_grow_zone(): can be called: > > get_page_from_freelist() > _deferred_grow_zone() > deferred_grow_zone() That's why page_alloc_init_late() needs spin_lock_irq(). If a CPU is holding deferred_zone_grow_lock with enabled interrupts and an interrupt comes in on that CPU and the CPU runs deferred_grow_zone() in its interrupt handler, we deadlock. lockdep knows about this bug and should have reported it. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
