Re: [PATCHv4 02/17] zram: do not use per-CPU compression streams

[Sergey Senozhatsky <senozhatsky@chromium.org>]

On (25/02/07 21:07), Yosry Ahmed wrote:
> I assume this problem is unique to zram and not zswap because zram can
> be used with normal IO (and then recurse through reclaim), while zswap
> is only reachable thorugh reclaim (which cannot recurse)?

I think I figured it out.  It appears that the problem was in lockdep
class key.  Both in zram and in zsmalloc I made the keys static:

 static void zram_slot_lock_init(struct zram *zram, u32 index)
 {
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
       static struct lock_class_key key;

        lockdep_init_map(&zram->table[index].lockdep_map, "zram-entry->lock",
                        &key, 0);
 #endif
 }

Which would put the locks to the same class from lockdep point of
view.  And that means that chains of locks from zram0 (mounted ext4)
and chains of locks from zram1 (swap device) would interleave, leading
to reports that made no sense.  Like ext4 writeback and blkdev_read and
handle_mm_fault->do_swap_page() would be parts of the same lock-chain *.

So I moved lockdep class keys to per-zram device and per-zsmalloc pool
to separate the lockdep chains.  Looks like that did the trick.


*

[ 1714.787676] [    T172] ======================================================
[ 1714.788905] [    T172] WARNING: possible circular locking dependency detected
[ 1714.790114] [    T172] 6.14.0-rc1-next-20250207+ #936 Not tainted
[ 1714.791150] [    T172] ------------------------------------------------------
[ 1714.792356] [    T172] kworker/u96:4/172 is trying to acquire lock:
[ 1714.793421] [    T172] ffff888114cf0598 (ptlock_ptr(ptdesc)#2){+.+.}-{3:3}, at: page_vma_mapped_walk+0x5c0/0x960
[ 1714.795174] [    T172]
                          but task is already holding lock:
[ 1714.796453] [    T172] ffffe8ffff981cf8 (&zstrm->lock){+.+.}-{4:4}, at: zcomp_stream_get+0x20/0x40 [zram]
[ 1714.798098] [    T172]
                          which lock already depends on the new lock.

[ 1714.799901] [    T172]                                                                                                                                                                                                                                                                                   the existing dependency chain (in reverse order) is:
[ 1714.801469] [    T172]
                          -> #3 (&zstrm->lock){+.+.}-{4:4}:
[ 1714.802750] [    T172]        lock_acquire.part.0+0x63/0x1a0
[ 1714.803712] [    T172]        __mutex_lock+0xaa/0xd40
[ 1714.804574] [    T172]        zcomp_stream_get+0x20/0x40 [zram]
[ 1714.805578] [    T172]        zram_read_from_zspool+0x84/0x140 [zram]
[ 1714.806673] [    T172]        zram_bio_read+0x56/0x2c0 [zram]
[ 1714.807641] [    T172]        __submit_bio+0x12d/0x1c0
[ 1714.808511] [    T172]        __submit_bio_noacct+0x7f/0x200
[ 1714.809468] [    T172]        mpage_readahead+0xdd/0x110
[ 1714.810360] [    T172]        read_pages+0x7a/0x1b0
[ 1714.811182] [    T172]        page_cache_ra_unbounded+0x19a/0x210
[ 1714.812215] [    T172]        force_page_cache_ra+0x92/0xb0
[ 1714.813161] [    T172]        filemap_get_pages+0x11f/0x440
[ 1714.814098] [    T172]        filemap_read+0xf6/0x400
[ 1714.814945] [    T172]        blkdev_read_iter+0x66/0x130
[ 1714.815860] [    T172]        vfs_read+0x266/0x370
[ 1714.816674] [    T172]        ksys_read+0x66/0xe0
[ 1714.817477] [    T172]        do_syscall_64+0x64/0x130
[ 1714.818344] [    T172]        entry_SYSCALL_64_after_hwframe+0x4b/0x53
[ 1714.819444] [    T172]
                          -> #2 (zram-entry->lock){+.+.}-{0:0}:
[ 1714.820769] [    T172]        lock_acquire.part.0+0x63/0x1a0
[ 1714.821734] [    T172]        zram_slot_free_notify+0x5c/0x80 [zram]
[ 1714.822811] [    T172]        swap_entry_range_free+0x115/0x1a0
[ 1714.823812] [    T172]        cluster_swap_free_nr+0xb9/0x150
[ 1714.824787] [    T172]        do_swap_page+0x80d/0xea0
[ 1714.825661] [    T172]        __handle_mm_fault+0x538/0x7a0
[ 1714.826592] [    T172]        handle_mm_fault+0xdf/0x240
[ 1714.827485] [    T172]        do_user_addr_fault+0x152/0x700
[ 1714.828432] [    T172]        exc_page_fault+0x66/0x1f0
[ 1714.829317] [    T172]        asm_exc_page_fault+0x22/0x30
[ 1714.830235] [    T172]        do_sys_poll+0x213/0x260
[ 1714.831090] [    T172]        __x64_sys_poll+0x44/0x190
[ 1714.831972] [    T172]        do_syscall_64+0x64/0x130
[ 1714.832846] [    T172]        entry_SYSCALL_64_after_hwframe+0x4b/0x53
[ 1714.833949] [    T172]
                          -> #1 (&cluster_info[i].lock){+.+.}-{3:3}:
[ 1714.835354] [    T172]        lock_acquire.part.0+0x63/0x1a0
[ 1714.836307] [    T172]        _raw_spin_lock+0x2c/0x40
[ 1714.837194] [    T172]        __swap_duplicate+0x5e/0x150
[ 1714.838123] [    T172]        swap_duplicate+0x1c/0x40
[ 1714.838980] [    T172]        try_to_unmap_one+0x6c4/0xd60
[ 1714.839901] [    T172]        rmap_walk_anon+0xe7/0x210
[ 1714.840774] [    T172]        try_to_unmap+0x76/0x80
[ 1714.841613] [    T172]        shrink_folio_list+0x487/0xad0
[ 1714.842546] [    T172]        evict_folios+0x247/0x800
[ 1714.843404] [    T172]        try_to_shrink_lruvec+0x1cd/0x2b0
[ 1714.844382] [    T172]        lru_gen_shrink_node+0xc3/0x190
[ 1714.845335] [    T172]        do_try_to_free_pages+0xee/0x4b0
[ 1714.846292] [    T172]        try_to_free_pages+0xea/0x280
[ 1714.847208] [    T172]        __alloc_pages_slowpath.constprop.0+0x296/0x970
[ 1714.848391] [    T172]        __alloc_frozen_pages_noprof+0x2b3/0x300
[ 1714.849475] [    T172]        __folio_alloc_noprof+0x10/0x30
[ 1714.850422] [    T172]        do_anonymous_page+0x69/0x4b0
[ 1714.851337] [    T172]        __handle_mm_fault+0x557/0x7a0
[ 1714.852265] [    T172]        handle_mm_fault+0xdf/0x240
[ 1714.853153] [    T172]        do_user_addr_fault+0x152/0x700
[ 1714.854099] [    T172]        exc_page_fault+0x66/0x1f0
[ 1714.854976] [    T172]        asm_exc_page_fault+0x22/0x30
[ 1714.855897] [    T172]        rep_movs_alternative+0x3a/0x60
[ 1714.856851] [    T172]        _copy_to_iter+0xe2/0x7a0
[ 1714.857719] [    T172]        get_random_bytes_user+0x95/0x150
[ 1714.858712] [    T172]        vfs_read+0x266/0x370
[ 1714.859512] [    T172]        ksys_read+0x66/0xe0
[ 1714.860301] [    T172]        do_syscall_64+0x64/0x130
[ 1714.861167] [    T172]        entry_SYSCALL_64_after_hwframe+0x4b/0x53
[ 1714.862270] [    T172]
                          -> #0 (ptlock_ptr(ptdesc)#2){+.+.}-{3:3}:
[ 1714.863656] [    T172]        check_prev_add+0xeb/0xca0
[ 1714.864532] [    T172]        __lock_acquire+0xf56/0x12c0
[ 1714.865446] [    T172]        lock_acquire.part.0+0x63/0x1a0
[ 1714.866399] [    T172]        _raw_spin_lock+0x2c/0x40
[ 1714.867258] [    T172]        page_vma_mapped_walk+0x5c0/0x960
[ 1714.868235] [    T172]        folio_referenced_one+0xd0/0x4a0
[ 1714.869205] [    T172]        __rmap_walk_file+0xbe/0x1b0
[ 1714.870119] [    T172]        folio_referenced+0x10b/0x140
[ 1714.871039] [    T172]        shrink_folio_list+0x72c/0xad0
[ 1714.871975] [    T172]        evict_folios+0x247/0x800
[ 1714.872851] [    T172]        try_to_shrink_lruvec+0x1cd/0x2b0
[ 1714.873842] [    T172]        lru_gen_shrink_node+0xc3/0x190
[ 1714.874806] [    T172]        do_try_to_free_pages+0xee/0x4b0
[ 1714.875779] [    T172]        try_to_free_pages+0xea/0x280
[ 1714.876699] [    T172]        __alloc_pages_slowpath.constprop.0+0x296/0x970
[ 1714.877897] [    T172]        __alloc_frozen_pages_noprof+0x2b3/0x300
[ 1714.878977] [    T172]        __alloc_pages_noprof+0xa/0x20
[ 1714.879907] [    T172]        alloc_zspage+0xe6/0x2c0 [zsmalloc]
[ 1714.880924] [    T172]        zs_malloc+0xd2/0x2b0 [zsmalloc]
[ 1714.881881] [    T172]        zram_write_page+0xfc/0x300 [zram]
[ 1714.882873] [    T172]        zram_bio_write+0xd1/0x1c0 [zram]
[ 1714.883845] [    T172]        __submit_bio+0x12d/0x1c0
[ 1714.884712] [    T172]        __submit_bio_noacct+0x7f/0x200
[ 1714.885667] [    T172]        ext4_io_submit+0x20/0x40
[ 1714.886532] [    T172]        ext4_do_writepages+0x3e3/0x8b0
[ 1714.887482] [    T172]        ext4_writepages+0xe8/0x280
[ 1714.888377] [    T172]        do_writepages+0xcf/0x260
[ 1714.889247] [    T172]        __writeback_single_inode+0x56/0x350
[ 1714.890273] [    T172]        writeback_sb_inodes+0x227/0x550
[ 1714.891239] [    T172]        __writeback_inodes_wb+0x4c/0xe0
[ 1714.892202] [    T172]        wb_writeback+0x2f2/0x3f0
[ 1714.893071] [    T172]        wb_do_writeback+0x227/0x2a0
[ 1714.893976] [    T172]        wb_workfn+0x56/0x1b0
[ 1714.894777] [    T172]        process_one_work+0x1eb/0x570
[ 1714.895698] [    T172]        worker_thread+0x1d1/0x3b0
[ 1714.896571] [    T172]        kthread+0xf9/0x200
[ 1714.897356] [    T172]        ret_from_fork+0x2d/0x50
[ 1714.898214] [    T172]        ret_from_fork_asm+0x11/0x20
[ 1714.899142] [    T172]
                          other info that might help us debug this:

[ 1714.900906] [    T172] Chain exists of:
                            ptlock_ptr(ptdesc)#2 --> zram-entry->lock --> &zstrm->lock

[ 1714.903183] [    T172]  Possible unsafe locking scenario:

[ 1714.904463] [    T172]        CPU0                    CPU1
[ 1714.905380] [    T172]        ----                    ----
[ 1714.906293] [    T172]   lock(&zstrm->lock);
[ 1714.907006] [    T172]                                lock(zram-entry->lock);
[ 1714.908204] [    T172]                                lock(&zstrm->lock);
[ 1714.909347] [    T172]   lock(ptlock_ptr(ptdesc)#2);
[ 1714.910179] [    T172]
                           *** DEADLOCK ***

[ 1714.911570] [    T172] 7 locks held by kworker/u96:4/172:
[ 1714.912472] [    T172]  #0: ffff88810165d548 ((wq_completion)writeback){+.+.}-{0:0}, at: process_one_work+0x433/0x570
[ 1714.914273] [    T172]  #1: ffffc90000683e40 ((work_completion)(&(&wb->dwork)->work)){+.+.}-{0:0}, at: process_one_work+0x1ad/0x570
[ 1714.916339] [    T172]  #2: ffff88810b93d0e0 (&type->s_umount_key#28){++++}-{4:4}, at: super_trylock_shared+0x16/0x50
[ 1714.918141] [    T172]  #3: ffff88810b93ab50 (&sbi->s_writepages_rwsem){.+.+}-{0:0}, at: do_writepages+0xcf/0x260
[ 1714.919877] [    T172]  #4: ffffe8ffff981cf8 (&zstrm->lock){+.+.}-{4:4}, at: zcomp_stream_get+0x20/0x40 [zram]
[ 1714.921573] [    T172]  #5: ffff888106809900 (&mapping->i_mmap_rwsem){++++}-{4:4}, at: __rmap_walk_file+0x161/0x1b0
[ 1714.923347] [    T172]  #6: ffffffff82347d40 (rcu_read_lock){....}-{1:3}, at: ___pte_offset_map+0x26/0x1b0
[ 1714.924981] [    T172]
                          stack backtrace:
[ 1714.925998] [    T172] CPU: 6 UID: 0 PID: 172 Comm: kworker/u96:4 Not tainted 6.14.0-rc1-next-20250207+ #936
[ 1714.926005] [    T172] Workqueue: writeback wb_workfn (flush-251:0)
[ 1714.926009] [    T172] Call Trace:
[ 1714.926013] [    T172]  <TASK>
[ 1714.926015] [    T172]  dump_stack_lvl+0x57/0x80
[ 1714.926018] [    T172]  print_circular_bug.cold+0x38/0x45
[ 1714.926021] [    T172]  check_noncircular+0x12e/0x150
[ 1714.926025] [    T172]  check_prev_add+0xeb/0xca0
[ 1714.926027] [    T172]  ? add_chain_cache+0x10c/0x480
[ 1714.926029] [    T172]  __lock_acquire+0xf56/0x12c0
[ 1714.926032] [    T172]  lock_acquire.part.0+0x63/0x1a0
[ 1714.926035] [    T172]  ? page_vma_mapped_walk+0x5c0/0x960
[ 1714.926036] [    T172]  ? page_vma_mapped_walk+0x5c0/0x960
[ 1714.926037] [    T172]  _raw_spin_lock+0x2c/0x40
[ 1714.926040] [    T172]  ? page_vma_mapped_walk+0x5c0/0x960
[ 1714.926041] [    T172]  page_vma_mapped_walk+0x5c0/0x960
[ 1714.926043] [    T172]  folio_referenced_one+0xd0/0x4a0
[ 1714.926046] [    T172]  __rmap_walk_file+0xbe/0x1b0
[ 1714.926047] [    T172]  folio_referenced+0x10b/0x140
[ 1714.926050] [    T172]  ? page_mkclean_one+0xc0/0xc0
[ 1714.926051] [    T172]  ? folio_get_anon_vma+0x220/0x220
[ 1714.926052] [    T172]  ? __traceiter_remove_migration_pte+0x50/0x50
[ 1714.926054] [    T172]  shrink_folio_list+0x72c/0xad0
[ 1714.926060] [    T172]  evict_folios+0x247/0x800
[ 1714.926064] [    T172]  try_to_shrink_lruvec+0x1cd/0x2b0
[ 1714.926066] [    T172]  lru_gen_shrink_node+0xc3/0x190
[ 1714.926068] [    T172]  ? mark_usage+0x61/0x110
[ 1714.926071] [    T172]  do_try_to_free_pages+0xee/0x4b0
[ 1714.926073] [    T172]  try_to_free_pages+0xea/0x280
[ 1714.926077] [    T172]  __alloc_pages_slowpath.constprop.0+0x296/0x970
[ 1714.926079] [    T172]  ? __lock_acquire+0x3d1/0x12c0
[ 1714.926081] [    T172]  ? get_page_from_freelist+0xd9/0x680
[ 1714.926083] [    T172]  ? match_held_lock+0x30/0xa0
[ 1714.926085] [    T172]  __alloc_frozen_pages_noprof+0x2b3/0x300
[ 1714.926088] [    T172]  __alloc_pages_noprof+0xa/0x20
[ 1714.926090] [    T172]  alloc_zspage+0xe6/0x2c0 [zsmalloc]
[ 1714.926092] [    T172]  ? zs_malloc+0xc5/0x2b0 [zsmalloc]
[ 1714.926094] [    T172]  ? __lock_release.isra.0+0x5e/0x180
[ 1714.926096] [    T172]  zs_malloc+0xd2/0x2b0 [zsmalloc]
[ 1714.926099] [    T172]  zram_write_page+0xfc/0x300 [zram]
[ 1714.926102] [    T172]  zram_bio_write+0xd1/0x1c0 [zram]
[ 1714.926105] [    T172]  __submit_bio+0x12d/0x1c0
[ 1714.926107] [    T172]  ? jbd2_journal_stop+0x145/0x320
[ 1714.926109] [    T172]  ? kmem_cache_free+0xb5/0x3e0
[ 1714.926112] [    T172]  ? lock_release+0x6b/0x130
[ 1714.926115] [    T172]  ? __submit_bio_noacct+0x7f/0x200
[ 1714.926116] [    T172]  __submit_bio_noacct+0x7f/0x200
[ 1714.926118] [    T172]  ext4_io_submit+0x20/0x40
[ 1714.926120] [    T172]  ext4_do_writepages+0x3e3/0x8b0
[ 1714.926122] [    T172]  ? lock_acquire.part.0+0x63/0x1a0
[ 1714.926124] [    T172]  ? do_writepages+0xcf/0x260
[ 1714.926127] [    T172]  ? ext4_writepages+0xe8/0x280
[ 1714.926128] [    T172]  ext4_writepages+0xe8/0x280
[ 1714.926130] [    T172]  do_writepages+0xcf/0x260
[ 1714.926133] [    T172]  ? find_held_lock+0x2b/0x80
[ 1714.926134] [    T172]  ? writeback_sb_inodes+0x1b8/0x550
[ 1714.926136] [    T172]  __writeback_single_inode+0x56/0x350
[ 1714.926138] [    T172]  writeback_sb_inodes+0x227/0x550
[ 1714.926143] [    T172]  __writeback_inodes_wb+0x4c/0xe0
[ 1714.926145] [    T172]  wb_writeback+0x2f2/0x3f0
[ 1714.926147] [    T172]  wb_do_writeback+0x227/0x2a0
[ 1714.926150] [    T172]  wb_workfn+0x56/0x1b0
[ 1714.926151] [    T172]  process_one_work+0x1eb/0x570
[ 1714.926154] [    T172]  worker_thread+0x1d1/0x3b0
[ 1714.926157] [    T172]  ? bh_worker+0x250/0x250
[ 1714.926159] [    T172]  kthread+0xf9/0x200
[ 1714.926161] [    T172]  ? kthread_fetch_affinity.isra.0+0x40/0x40
[ 1714.926163] [    T172]  ret_from_fork+0x2d/0x50
[ 1714.926165] [    T172]  ? kthread_fetch_affinity.isra.0+0x40/0x40
[ 1714.926166] [    T172]  ret_from_fork_asm+0x11/0x20
[ 1714.926170] [    T172]  </TASK>