From: "Hailong.Liu" <hailong.liu@xxxxxxxx>
The function xa_for_each() in _vm_unmap_aliases() loops through all
vbs. However, since commit 062eacf57ad9 ("mm: vmalloc: remove a global
vmap_blocks xarray") the vb from xarray may not be on the corresponding
CPU vmap_block_queue. Consequently, purge_fragmented_block() might
use the wrong vbq->lock to protect the free list, leading to vbq->free
breakage.
Incorrect lock protection can exhaust all vmalloc space as follows:
CPU0 CPU1
+--------------------------------------------+
| +--------------------+ +-----+ |
+--> | |---->| |------+
| CPU1:vbq free_list | | vb1 |
+--- | |<----| |<-----+
| +--------------------+ +-----+ |
+--------------------------------------------+
_vm_unmap_aliases() vb_alloc()
new_vmap_block()
xa_for_each(&vbq->vmap_blocks, idx, vb)
--> vb in CPU1:vbq->freelist
purge_fragmented_block(vb)
spin_lock(&vbq->lock) spin_lock(&vbq->lock)
--> use CPU0:vbq->lock --> use CPU1:vbq->lock
list_del_rcu(&vb->free_list) list_add_tail_rcu(&vb->free_list, &vbq->free)
__list_del(vb->prev, vb->next)
next->prev = prev
+--------------------+
| |
| CPU1:vbq free_list |
+---| |<--+
| +--------------------+ |
+----------------------------+
__list_add(new, head->prev, head)
+--------------------------------------------+
| +--------------------+ +-----+ |
+--> | |---->| |------+
| CPU1:vbq free_list | | vb2 |
+--- | |<----| |<-----+
| +--------------------+ +-----+ |
+--------------------------------------------+
prev->next = next
+--------------------------------------------+
|----------------------------+ |
| +--------------------+ | +-----+ |
+--> | |--+ | |------+
| CPU1:vbq free_list | | vb2 |
+--- | |<----| |<-----+
| +--------------------+ +-----+ |
+--------------------------------------------+
Here’s a list breakdown. All vbs, which were to be added to
‘prev’, cannot be used by list_for_each_entry_rcu(vb, &vbq->free,
free_list) in vb_alloc(). Thus, vmalloc space is exhausted.
This issue affects both erofs and f2fs, the stacktrace is as follows:
erofs:
[<ffffffd4ffb93ad4>] __switch_to+0x174
[<ffffffd4ffb942f0>] __schedule+0x624
[<ffffffd4ffb946f4>] schedule+0x7c
[<ffffffd4ffb947cc>] schedule_preempt_disabled+0x24
[<ffffffd4ffb962ec>] __mutex_lock+0x374
[<ffffffd4ffb95998>] __mutex_lock_slowpath+0x14
[<ffffffd4ffb95954>] mutex_lock+0x24
[<ffffffd4fef2900c>] reclaim_and_purge_vmap_areas+0x44
[<ffffffd4fef25908>] alloc_vmap_area+0x2e0
[<ffffffd4fef24ea0>] vm_map_ram+0x1b0
[<ffffffd4ff1b46f4>] z_erofs_lz4_decompress+0x278
[<ffffffd4ff1b8ac4>] z_erofs_decompress_queue+0x650
[<ffffffd4ff1b8328>] z_erofs_runqueue+0x7f4
[<ffffffd4ff1b66a8>] z_erofs_read_folio+0x104
[<ffffffd4feeb6fec>] filemap_read_folio+0x6c
[<ffffffd4feeb68c4>] filemap_fault+0x300
[<ffffffd4fef0ecac>] __do_fault+0xc8
[<ffffffd4fef0c908>] handle_mm_fault+0xb38
[<ffffffd4ffb9f008>] do_page_fault+0x288
[<ffffffd4ffb9ed64>] do_translation_fault[jt]+0x40
[<ffffffd4fec39c78>] do_mem_abort+0x58
[<ffffffd4ffb8c3e4>] el0_ia+0x70
[<ffffffd4ffb8c260>] el0t_64_sync_handler[jt]+0xb0
[<ffffffd4fec11588>] ret_to_user[jt]+0x0
f2fs:
[<ffffffd4ffb93ad4>] __switch_to+0x174
[<ffffffd4ffb942f0>] __schedule+0x624
[<ffffffd4ffb946f4>] schedule+0x7c
[<ffffffd4ffb947cc>] schedule_preempt_disabled+0x24
[<ffffffd4ffb962ec>] __mutex_lock+0x374
[<ffffffd4ffb95998>] __mutex_lock_slowpath+0x14
[<ffffffd4ffb95954>] mutex_lock+0x24
[<ffffffd4fef2900c>] reclaim_and_purge_vmap_areas+0x44
[<ffffffd4fef25908>] alloc_vmap_area+0x2e0
[<ffffffd4fef24ea0>] vm_map_ram+0x1b0
[<ffffffd4ff1a3b60>] f2fs_prepare_decomp_mem+0x144
[<ffffffd4ff1a6c24>] f2fs_alloc_dic+0x264
[<ffffffd4ff175468>] f2fs_read_multi_pages+0x428
[<ffffffd4ff17b46c>] f2fs_mpage_readpages+0x314
[<ffffffd4ff1785c4>] f2fs_readahead+0x50
[<ffffffd4feec3384>] read_pages+0x80
[<ffffffd4feec32c0>] page_cache_ra_unbounded+0x1a0
[<ffffffd4feec39e8>] page_cache_ra_order+0x274
[<ffffffd4feeb6cec>] do_sync_mmap_readahead+0x11c
[<ffffffd4feeb6764>] filemap_fault+0x1a0
[<ffffffd4ff1423bc>] f2fs_filemap_fault+0x28
[<ffffffd4fef0ecac>] __do_fault+0xc8
[<ffffffd4fef0c908>] handle_mm_fault+0xb38
[<ffffffd4ffb9f008>] do_page_fault+0x288
[<ffffffd4ffb9ed64>] do_translation_fault[jt]+0x40
[<ffffffd4fec39c78>] do_mem_abort+0x58
[<ffffffd4ffb8c3e4>] el0_ia+0x70
[<ffffffd4ffb8c260>] el0t_64_sync_handler[jt]+0xb0
[<ffffffd4fec11588>] ret_to_user[jt]+0x0
To fix this, replace xa_for_each() with list_for_each_entry_rcu()
which reverts commit fc1e0d980037 ("mm/vmalloc: prevent stale TLBs
in fully utilized blocks")
Signed-off-by: Hailong.Liu <hailong.liu@xxxxxxxx>
---
mm/vmalloc.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)
diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 125427cbdb87..4c65e9678b83 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -2806,10 +2806,9 @@ static void _vm_unmap_aliases(unsigned long start, unsigned long end, int flush)
for_each_possible_cpu(cpu) {
struct vmap_block_queue *vbq = &per_cpu(vmap_block_queue, cpu);
struct vmap_block *vb;
- unsigned long idx;
rcu_read_lock();
- xa_for_each(&vbq->vmap_blocks, idx, vb) {
+ list_for_each_entry_rcu(vb, &vbq->free, free_list) {
spin_lock(&vb->lock);
/*
---
Changes since v1 [1]:
- add runtime effect in commit msg, per Andrew.
[1] https://lore.kernel.org/all/20240530093108.4512-1-hailong.liu@xxxxxxxx/
BTW Reverting other people’s submissions is a foolish act. But we need a mapping
from vmap_block to vmap_block_queue, I saw zhaoyang already send a patch
https://patchwork.kernel.org/project/linux-mm/patch/20240531005007.1600287-1-zhaoyang.huang@xxxxxxxxxx/
use cpuid. pls free to use my commit message here to help others
clarify the issue.
fc1e0d980037 ("mm/vmalloc: prevent stale TLBs in fully utilized blocks")
IMO, if caller could call vb_free, it would be not used address again.
so I don't know whether we need to flush TLB here. and loop through from free
list looks more resonable to me.
--
2.34.1
