Hi.
While running v5.10-rc5-rt11 I bumped into the following:
```
BUG: scheduling while atomic: git/18695/0x00000002
Preemption disabled at:
[<ffffffffbb93fcb3>] z3fold_zpool_malloc+0x463/0x6e0
…
Call Trace:
dump_stack+0x6d/0x88
__schedule_bug.cold+0x88/0x96
__schedule+0x69e/0x8c0
preempt_schedule_lock+0x51/0x150
rt_spin_lock_slowlock_locked+0x117/0x2c0
rt_spin_lock_slowlock+0x58/0x80
rt_spin_lock+0x2a/0x40
z3fold_zpool_malloc+0x4c1/0x6e0
zswap_frontswap_store+0x39c/0x980
__frontswap_store+0x6e/0xf0
swap_writepage+0x39/0x70
shmem_writepage+0x31b/0x490
pageout+0xf4/0x350
shrink_page_list+0xa28/0xcc0
shrink_inactive_list+0x300/0x690
shrink_lruvec+0x59a/0x770
shrink_node+0x2d6/0x8d0
do_try_to_free_pages+0xda/0x530
try_to_free_pages+0xff/0x260
__alloc_pages_slowpath.constprop.0+0x3d5/0x1230
__alloc_pages_nodemask+0x2f6/0x350
allocate_slab+0x3da/0x660
___slab_alloc+0x4ff/0x760
__slab_alloc.constprop.0+0x7a/0x100
kmem_cache_alloc+0x27b/0x2c0
__d_alloc+0x22/0x230
d_alloc_parallel+0x67/0x5e0
__lookup_slow+0x5c/0x150
path_lookupat+0x2ea/0x4d0
filename_lookup+0xbf/0x210
vfs_statx.constprop.0+0x4d/0x110
__do_sys_newlstat+0x3d/0x80
do_syscall_64+0x33/0x40
entry_SYSCALL_64_after_hwframe+0x44/0xa9
```
The preemption seems to be disabled here:
```
$ scripts/faddr2line mm/z3fold.o z3fold_zpool_malloc+0x463
z3fold_zpool_malloc+0x463/0x6e0:
add_to_unbuddied at mm/z3fold.c:645
(inlined by) z3fold_alloc at mm/z3fold.c:1195
(inlined by) z3fold_zpool_malloc at mm/z3fold.c:1737
```
The call to the rt_spin_lock() seems to be here:
```
$ scripts/faddr2line mm/z3fold.o z3fold_zpool_malloc+0x4c1
z3fold_zpool_malloc+0x4c1/0x6e0:
add_to_unbuddied at mm/z3fold.c:649
(inlined by) z3fold_alloc at mm/z3fold.c:1195
(inlined by) z3fold_zpool_malloc at mm/z3fold.c:1737
```
Or, in source code:
```
639 /* Add to the appropriate unbuddied list */
640 static inline void add_to_unbuddied(struct z3fold_pool *pool,
641 struct z3fold_header *zhdr)
642 {
643 if (zhdr->first_chunks == 0 || zhdr->last_chunks == 0 ||
644 zhdr->middle_chunks == 0) {
645 struct list_head *unbuddied = get_cpu_ptr(pool->unbuddied);
646
647 int freechunks = num_free_chunks(zhdr);
648 spin_lock(&pool->lock);
649 list_add(&zhdr->buddy, &unbuddied[freechunks]);
650 spin_unlock(&pool->lock);
651 zhdr->cpu = smp_processor_id();
652 put_cpu_ptr(pool->unbuddied);
653 }
654 }
```
Shouldn't the list manipulation be protected with
local_lock+this_cpu_ptr instead of get_cpu_ptr+spin_lock?
Thanks.
--
Oleksandr Natalenko (post-factum)
