Re: [patch 01/28] cpu alloc: The allocator

Christoph Lameter
2007-11-08T18:50:15Z

On Thu, 8 Nov 2007, Christoph Lameter wrote:

> > Also, looking at the lock usage, this thing is not IRQ safe, so it
> > should not be called from hardirq context. Please document this.

Well I went the other way and made it work like the slab allocators.

cpu_alloc: Make it irq safe

Use the same method as used in SLAB/SLUB to make the allocator interrupt safe.
disable interrupts when allocator metadata is processed. Reenable interrupts
during page allocator calls if __GFP_WAIT is set in the flags passed to the
allocator.

Signed-off-by: Christoph Lameter <clameter@sgi.com>

---
mm/cpu_alloc.c | 16 +++++++++++-----
1 file changed, 11 insertions(+), 5 deletions(-)

Index: linux-2.6/mm/cpu_alloc.c
===================================================================
--- linux-2.6.orig/mm/cpu_alloc.c 2007-11-07 16:49:40.069701326 -0800
+++ linux-2.6/mm/cpu_alloc.c 2007-11-08 10:45:43.172294260 -0800
@@ -186,6 +186,8 @@ static int expand_cpu_area(gfp_t flags)
goto out;

spin_unlock(&cpu_alloc_map_lock);
+ if (flags & __GFP_WAIT)
+ local_irq_enable();

/*
* Determine the size of the bit map needed
@@ -212,6 +214,8 @@ static int expand_cpu_area(gfp_t flags)
goto out;
}

+ if (flags & __GFP_WAIT)
+ local_irq_disable();
spin_lock(&cpu_alloc_map_lock);

/*
@@ -312,10 +316,11 @@ void *cpu_alloc(unsigned long size, gfp_
void *ptr;
int first;
unsigned long map_size;
+ unsigned long flags;

BUG_ON(gfpflags & ~(GFP_RECLAIM_MASK | __GFP_ZERO));

- spin_lock(&cpu_alloc_map_lock);
+ spin_lock_irqsave(&cpu_alloc_map_lock, flags);

restart:
map_size = PAGE_SIZE << cpu_alloc_map_order;
@@ -358,7 +363,7 @@ restart:
units_free -= units;
__count_vm_events(CPU_BYTES, units * UNIT_SIZE);

- spin_unlock(&cpu_alloc_map_lock);
+ spin_unlock_irqrestore(&cpu_alloc_map_lock, flags);

ptr = cpu_area + start * UNIT_SIZE;

@@ -372,7 +377,7 @@ restart:
return ptr;

out_of_memory:
- spin_unlock(&cpu_alloc_map_lock);
+ spin_unlock_irqrestore(&cpu_alloc_map_lock, flags);
return NULL;
}
EXPORT_SYMBOL(cpu_alloc);
@@ -386,13 +391,14 @@ void cpu_free(void *start, unsigned long
int units = size_to_units(size);
int index;
u8 *p = start;
+ unsigned long flags;

BUG_ON(p < cpu_area);
index = (p - cpu_area) / UNIT_SIZE;
BUG_ON(!test_bit(index, cpu_alloc_map) ||
index >= units_total);

- spin_lock(&cpu_alloc_map_lock);
+ spin_lock_irqsave(&cpu_alloc_map_lock, flags);

clear_map(index, units);
units_free += units;
@@ -400,6 +406,6 @@ void cpu_free(void *start, unsigned long
if (index < first_free)
first_free = index;

- spin_unlock(&cpu_alloc_map_lock);
+ spin_unlock_irqrestore(&cpu_alloc_map_lock, flags);
}
EXPORT_SYMBOL(cpu_free);