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mm/vmalloc: check free space in vmap_block lockless

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vb_alloc() unconditionally locks a vmap_block on the free list to check
the free space.

This can be done locklessly because vmap_block::free never increases, it's
only decreased on allocations.

Check the free space lockless and only if that succeeds, recheck under the
lock.

Link: https://lkml.kernel.org/r/20230525124504.750481992@linutronix.de
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Lorenzo Stoakes <lstoakes@gmail.com>
Reviewed-by: Baoquan He <bhe@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Thomas Gleixner 2023-05-25 14:57:07 +02:00 committed by Andrew Morton
parent a09fad96ff
commit 43d7650234
1 changed files with 4 additions and 1 deletions
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5
mm/vmalloc.c
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@ -2168,6 +2168,9 @@ static void *vb_alloc(unsigned long size, gfp_t gfp_mask)
list_for_each_entry_rcu(vb, &vbq->free, free_list) {
unsigned long pages_off;
if (READ_ONCE(vb->free) < (1UL << order))
continue;
spin_lock(&vb->lock);
if (vb->free < (1UL << order)) {
spin_unlock(&vb->lock);
@ -2176,7 +2179,7 @@ static void *vb_alloc(unsigned long size, gfp_t gfp_mask)
pages_off = VMAP_BBMAP_BITS - vb->free;
vaddr = vmap_block_vaddr(vb->va->va_start, pages_off);
vb->free -= 1UL << order;
WRITE_ONCE(vb->free, vb->free - (1UL << order));
bitmap_set(vb->used_map, pages_off, (1UL << order));
if (vb->free == 0) {
spin_lock(&vbq->lock);