[moderation/CI] Re: Virtual Swap Space

[syzbot ci <syzbot+cib572d1edc7b20732@syzkaller.appspotmail.com>]

syzbot ci has tested the following series

[v3] Virtual Swap Space
https://lore.kernel.org/all/20260208215839.87595-1-nphamcs@gmail.com
* [PATCH v3 01/20] mm/swap: decouple swap cache from physical swap infrastructure
* [PATCH v3 02/20] swap: rearrange the swap header file
* [PATCH v3 03/20] mm: swap: add an abstract API for locking out swapoff
* [PATCH v3 04/20] zswap: add new helpers for zswap entry operations
* [PATCH v3 05/20] mm/swap: add a new function to check if a swap entry is in swap cached.
* [PATCH v3 06/20] mm: swap: add a separate type for physical swap slots
* [PATCH v3 07/20] mm: create scaffolds for the new virtual swap implementation
* [PATCH v3 08/20] zswap: prepare zswap for swap virtualization
* [PATCH v3 09/20] mm: swap: allocate a virtual swap slot for each swapped out page
* [PATCH v3 10/20] swap: move swap cache to virtual swap descriptor
* [PATCH v3 11/20] zswap: move zswap entry management to the virtual swap descriptor
* [PATCH v3 12/20] swap: implement the swap_cgroup API using virtual swap
* [PATCH v3 13/20] swap: manage swap entry lifecycle at the virtual swap layer
* [PATCH v3 14/20] mm: swap: decouple virtual swap slot from backing store
* [PATCH v3 15/20] zswap: do not start zswap shrinker if there is no physical swap slots
* [PATCH v3 16/20] swap: do not unnecesarily pin readahead swap entries
* [PATCH v3 17/20] swapfile: remove zeromap bitmap
* [PATCH v3 18/20] memcg: swap: only charge physical swap slots
* [PATCH v3 19/20] swap: simplify swapoff using virtual swap
* [PATCH v3 20/20] swapfile: replace the swap map with bitmaps

and found the following issue:
possible deadlock in vswap_iter

Full report is available here:
https://ci.syzbot.org/series/b9defda6-daec-4c41-bbf9-7d3b7fabd7cb

***

possible deadlock in vswap_iter

tree:      bpf
URL:       https://kernel.googlesource.com/pub/scm/linux/kernel/git/bpf/bpf.git
base:      05f7e89ab9731565d8a62e3b5d1ec206485eeb0b
arch:      amd64
compiler:  Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
config:    https://ci.syzbot.org/builds/f444cfbe-4ce0-4917-94aa-3a8bd96ee376/config
C repro:   https://ci.syzbot.org/findings/7b8c50b1-47d6-42e0-bcfc-814e7b3bb596/c_repro
syz repro: https://ci.syzbot.org/findings/7b8c50b1-47d6-42e0-bcfc-814e7b3bb596/syz_repro

loop0: detected capacity change from 0 to 764
============================================
WARNING: possible recursive locking detected
syzkaller #0 Not tainted
--------------------------------------------
syz-executor625/5806 is trying to acquire lock:
ffff88811884c018 (&cluster->lock){+.+.}-{3:3}, at: spin_lock include/linux/spinlock.h:351 [inline]
ffff88811884c018 (&cluster->lock){+.+.}-{3:3}, at: vswap_iter+0xfa/0x1b0 mm/vswap.c:274

but task is already holding lock:
ffff88811884c018 (&cluster->lock){+.+.}-{3:3}, at: spin_lock_irq include/linux/spinlock.h:376 [inline]
ffff88811884c018 (&cluster->lock){+.+.}-{3:3}, at: swap_cache_lock_irq+0xe2/0x190 mm/vswap.c:1586

other info that might help us debug this:
 Possible unsafe locking scenario:

       CPU0
       ----
  lock(&cluster->lock);
  lock(&cluster->lock);

 *** DEADLOCK ***

 May be due to missing lock nesting notation

3 locks held by syz-executor625/5806:
 #0: ffff888174bc2800 (&mm->mmap_lock){++++}-{4:4}, at: mmap_read_lock include/linux/mmap_lock.h:391 [inline]
 #0: ffff888174bc2800 (&mm->mmap_lock){++++}-{4:4}, at: madvise_lock+0x152/0x2e0 mm/madvise.c:1789
 #1: ffff88811884c018 (&cluster->lock){+.+.}-{3:3}, at: spin_lock_irq include/linux/spinlock.h:376 [inline]
 #1: ffff88811884c018 (&cluster->lock){+.+.}-{3:3}, at: swap_cache_lock_irq+0xe2/0x190 mm/vswap.c:1586
 #2: ffffffff8e55a360 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline]
 #2: ffffffff8e55a360 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:867 [inline]
 #2: ffffffff8e55a360 (rcu_read_lock){....}-{1:3}, at: vswap_cgroup_record+0x40/0x290 mm/vswap.c:1925

stack backtrace:


***

If these findings have caused you to resend the series or submit a
separate fix, please add the following tag to your commit message:
  Tested-by: syzbot@syzkaller.appspotmail.com

---
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