From 3f80492001aa64ac585016050ace8680611c2e20 Mon Sep 17 00:00:00 2001 From: Sebastian Andrzej Siewior Date: Thu, 12 May 2022 20:23:08 -0700 Subject: [PATCH] mm/vmalloc: use raw_cpu_ptr() for vmap_block_queue access The per-CPU resource vmap_block_queue is accessed via get_cpu_var(). That macro disables preemption and then loads the pointer from the current CPU. This doesn't work on PREEMPT_RT because a spinlock_t is later accessed within the preempt-disable section. There is no need to disable preemption while accessing the per-CPU struct vmap_block_queue because the list is protected with a spinlock_t. The per-CPU struct is also accessed cross-CPU in purge_fragmented_blocks(). It is possible that by using raw_cpu_ptr() the code migrates to another CPU and uses struct from another CPU. This is fine because the list is locked and the locked section is very short. Use raw_cpu_ptr() to access vmap_block_queue. Link: https://lkml.kernel.org/r/YnKx3duAB53P7ojN@linutronix.de Signed-off-by: Sebastian Andrzej Siewior Cc: Uladzislau Rezki (Sony) Cc: Thomas Gleixner Signed-off-by: Andrew Morton --- mm/vmalloc.c | 6 ++---- 1 file changed, 2 insertions(+), 4 deletions(-) diff --git a/mm/vmalloc.c b/mm/vmalloc.c index 5b59ccafcd46..07db42455dd4 100644 --- a/mm/vmalloc.c +++ b/mm/vmalloc.c @@ -1938,11 +1938,10 @@ static void *new_vmap_block(unsigned int order, gfp_t gfp_mask) return ERR_PTR(err); } - vbq = &get_cpu_var(vmap_block_queue); + vbq = raw_cpu_ptr(&vmap_block_queue); spin_lock(&vbq->lock); list_add_tail_rcu(&vb->free_list, &vbq->free); spin_unlock(&vbq->lock); - put_cpu_var(vmap_block_queue); return vaddr; } @@ -2021,7 +2020,7 @@ static void *vb_alloc(unsigned long size, gfp_t gfp_mask) order = get_order(size); rcu_read_lock(); - vbq = &get_cpu_var(vmap_block_queue); + vbq = raw_cpu_ptr(&vmap_block_queue); list_for_each_entry_rcu(vb, &vbq->free, free_list) { unsigned long pages_off; @@ -2044,7 +2043,6 @@ static void *vb_alloc(unsigned long size, gfp_t gfp_mask) break; } - put_cpu_var(vmap_block_queue); rcu_read_unlock(); /* Allocate new block if nothing was found */