[Bug 207873] New: BUG at swapops + rcu stall + soft lockup at running btrfs test suite (TEST=013\* ./misc-tests.sh)

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https://bugzilla.kernel.org/show_bug.cgi?id=207873

            Bug ID: 207873
           Summary: BUG at swapops + rcu stall + soft lockup at running
                    btrfs test suite (TEST=013\* ./misc-tests.sh)
           Product: Platform Specific/Hardware
           Version: 2.5
    Kernel Version: 5.7-rc6
          Hardware: PPC-32
                OS: Linux
              Tree: Mainline
            Status: NEW
          Severity: normal
          Priority: P1
         Component: PPC-32
          Assignee: platform_ppc-32@kernel-bugs.osdl.org
          Reporter: erhard_f@mailbox.org
                CC: fs_btrfs@kernel-bugs.osdl.org
        Regression: No

Created attachment 289253
  --> https://bugzilla.kernel.org/attachment.cgi?id=289253&action=edit
kernel .config (5.7-rc6, PowerMac G4 DP)

The bug is triggered by running "TEST=013\* ./misc-tests.sh" of btrfs-progs
test suite, built from git master:

 # git clone https://github.com/kdave/btrfs-progs && cd btrfs-progs/
 # ./autogen.sh && ./configure --disable-documentation
 # make && make fssum
 # cd tests/
 # TEST=013\* ./misc-tests.sh

The G4 crashes and the reboot timer kicks in. Before it shows a series of stack
traces, starting with the "kernel BUG at include/linux/swapops.h:197!"-part
from bug #207221. After that I get an rcu stall and a soft lockup. For the full
stacktrace have a look at the transcript of both screenshots.

[...]
rcu: INFO: rcu_sched self-detected stall on CPU
rcu: o1-....: (7799 ticks this GP) idle=a06/1/0x40000002 soft irq=11075/11075
fqs=2599
o(t=7804 jiffies g=21629 q=59)
Task dump for CPU 1:
dd              R  running task        0  2200    394 0x0000000c
Call Trace:
[f49fb458] [c00fcddc] sched_show_task+0x3bc/Ox3fe (unreliable)
[f49fb498] [c01c650c] rcu_dump_cpu_stacks+0x228/0x23c
[f49fb4e8] [c01c2e18] rcu_sched_clock_irq+0x81c/0x1360
[f49fb568] [c01d8940] update_process_times+0x2c/0x98
[f49fb588] [c02027d4] tick_sched_timer+0x128/0x1d8
[f49fb5a8] [c01dc49c] __hrtimer_run_queues+0x490/Oxae8
[f49fb698] [c01dd788] hrtimer_interrupt+0x278/0x520
[f49fb6f8] [c001710c] timer_interrupt+0x374/0xb4c
[f49fb738] [c002c5e4] ret_from_except+0x0/0x14
--- interrupt: 901 at do_raw_spin_lock+0x1c8/0x2cc
    LR = do_raw_spin_lock+0x1a4/0x2cc
[f49fb800] [c0180e0c] do_raw_spin_lock+0x188/0x2cc (unrelable)
[f49fb830] [c0428890] unmap_page_range+0x244/0xb08
[f49fb910] [c0429610] unmap_vmas+0x94/0xdc
[f49fb930] [c043c25c] exit_mmap+0x340/0x46c
[f49fba20] [c0078260] __mmput+0x78/0x360
[f49fba50] [c0090514] do_exit+0x9c4/0x21fc
[f49fbb20] [c0019d38] user_single_step_report+0x0/0x74
[f49fbb70] [c002c5e0] ret_from_except+0x0/0x4
--- interrupt: 700 at __migration_entry_wait+0x13c/0x198
    LR = __migration_entry_wait+0xf0/0x198
[f49fbc58] [c042c0f0] do_swap_page+0x1f0/0x198
[f49fbd28] [c042e7e4] handle_mm_fault+0x794/0x16f4
[f49fbe48] [c0039868] do_page_fault+0xf50/0x12f8
[f49fbf38] [c002c468] handle_page_fault+0x10/0x3c
--- interrupt: 301 at 0x87e378
    LR = 0x87e33c
[...]

I don't know wether this is a btrfs bug, or a bug only triggered by this
specific test. So I am filing this as platform specific as I have not seen it
on x86 yet.

Unlike bug #207221 KASAN is enabled here, so the stack trace looks slightly
different.

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