The patch titled
Subject: mm/vmalloc: check free space in vmap_block lockless
has been added to the -mm mm-unstable branch. Its filename is
mm-vmalloc-check-free-space-in-vmap_block-lockless.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-vmalloc-check-free-space-in-vmap_block-lockless.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Subject: mm/vmalloc: check free space in vmap_block lockless
Date: Thu, 25 May 2023 14:57:07 +0200 (CEST)
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@xxxxxxxxxxxxx
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Reviewed-by: Uladzislau Rezki (Sony) <urezki@xxxxxxxxx>
Cc: Baoquan He <bhe@xxxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
Cc: Lorenzo Stoakes <lstoakes@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/vmalloc.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
--- a/mm/vmalloc.c~mm-vmalloc-check-free-space-in-vmap_block-lockless
+++ a/mm/vmalloc.c
@@ -2168,6 +2168,9 @@ static void *vb_alloc(unsigned long size
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
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);
_
Patches currently in -mm which might be from tglx@xxxxxxxxxxxxx are
mm-vmalloc-prevent-stale-tlbs-in-fully-utilized-blocks.patch
mm-vmalloc-avoid-iterating-over-per-cpu-vmap-blocks-twice.patch
mm-vmalloc-prevent-flushing-dirty-space-over-and-over.patch
mm-vmalloc-check-free-space-in-vmap_block-lockless.patch
mm-vmalloc-add-missing-read-write_once-annotations.patch
mm-vmalloc-dont-purge-usable-blocks-unnecessarily.patch
