From 43d7650234c62201ba3ca5b731226b0b189989a8 Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Thu, 25 May 2023 14:57:07 +0200 Subject: [PATCH] mm/vmalloc: check free space in vmap_block lockless 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 Reviewed-by: Uladzislau Rezki (Sony) Reviewed-by: Christoph Hellwig Reviewed-by: Lorenzo Stoakes Reviewed-by: Baoquan He Signed-off-by: Andrew Morton --- mm/vmalloc.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/mm/vmalloc.c b/mm/vmalloc.c index ad9a1d9e314f..679112e2ffd2 100644 --- a/mm/vmalloc.c +++ b/mm/vmalloc.c @@ -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);