On Sat, Nov 28, 2020 at 03:05:24PM +0100, Oleksandr Natalenko wrote: > 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)
Forgot to Cc linux-rt-users@, sorry. -- Oleksandr Natalenko (post-factum)