[zswap?] BUG: sleeping function called from invalid context at kernel/cgroup/rstat.c:421

[Zenghui Yu <zenghui.yu@linux.dev>]

Hi all,

The following splat was triggered on the mainline kernel:

 BUG: sleeping function called from invalid context at kernel/cgroup/rstat.c:421
 in_atomic(): 0, irqs_disabled(): 0, non_block: 0, pid: 1126, name: cat
 preempt_count: 0, expected: 0
 RCU nest depth: 1, expected: 0
 CPU: 7 UID: 0 PID: 1126 Comm: cat Kdump: loaded Not tainted 7.1.0-rc7-00056-gacb7500801e9-dirty #304 PREEMPT 
 Hardware name: QEMU QEMU Virtual Machine, BIOS edk2-stable202408-prebuilt.qemu.org 08/13/2024
 Call trace:
  show_stack+0x18/0x24 (C)
  dump_stack_lvl+0x78/0x90
  dump_stack+0x18/0x24
  __might_resched+0x114/0x170
  __might_sleep+0x48/0x98
  css_rstat_flush+0x54/0x564
  mem_cgroup_flush_stats+0x9c/0xb0
  zswap_shrinker_count+0xe4/0x1e4
  shrinker_debugfs_count_show+0xd8/0x268
  seq_read_iter+0x1b8/0x4ac
  seq_read+0xe0/0x11c
  full_proxy_read+0x6c/0xa8
  vfs_read+0xc0/0x2fc
  ksys_read+0x68/0xfc
  __arm64_sys_read+0x1c/0x28
  invoke_syscall+0x54/0x110
  el0_svc_common.constprop.0+0x40/0xe0
  do_el0_svc+0x1c/0x28
  el0_svc+0x38/0x128
  el0t_64_sync_handler+0xa0/0xe4
  el0t_64_sync+0x198/0x19c

The kernel is built with arm64's virt.config plus

+CONFIG_DEBUG_ATOMIC_SLEEP=y
+CONFIG_SHRINKER_DEBUG=y
+CONFIG_ZSWAP=y

I can reproduce the issue with the following steps:

    $ echo Y > /sys/module/zswap/parameters/enabled
    $ echo Y > /sys/module/zswap/parameters/shrinker_enabled
    $ cat /sys/kernel/debug/shrinker/mm-zswap-60/count

Please have a look.

Thanks,
Zenghui