On Mon, 2020-09-14 at 12:17 -0400, Qian Cai wrote:
> On Thu, 2020-09-10 at 19:33 +0100, Matthew Wilcox (Oracle) wrote:
> > Instead of calling find_get_entry() for every page index, use an XArray
> > iterator to skip over NULL entries, and avoid calling get_page(),
> > because we only want the swap entries.
> >
> > Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
> > Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>
>
> Reverting the "Return head pages from find_*_entry" patchset [1] up to this
> patch fixed the issue that LTP madvise06 test [2] would trigger endless soft-
> lockups below. It does not help after applied patches fixed other separate
> issues in the patchset [3][4].
Forgot to send this piece of RCU stall traces as well which might help
debugging.
00: [ 2852.137748] madvise06 (62712): drop_caches: 3
01: [ 2928.208367] rcu: INFO: rcu_sched self-detected stall on CPU
01: [ 2928.210083] rcu: 1-....: (6499 ticks this GP) idle=036/1/0x4000000000
01: 000002 softirq=1741392/1741392 fqs=3161
01: [ 2928.210610] (t=6500 jiffies g=610849 q=12529)
01: [ 2928.210620] Task dump for CPU 1:
01: [ 2928.210630] task:madvise06 state:R running task stack:53320 pi
01: d:62712 ppid: 62711 flags:0x00000004
01: [ 2928.210676] Call Trace:
01: [ 2928.210693] [<00000000af57ec88>] show_stack+0x158/0x1f0
01: [ 2928.210703] [<00000000ae55b692>] sched_show_task+0x3d2/0x4c8
01: [ 2928.210710] [<00000000af5846aa>] rcu_dump_cpu_stacks+0x26a/0x2a8
01: [ 2928.210718] [<00000000ae64fa62>] rcu_sched_clock_irq+0x1c92/0x2188
01: [ 2928.210726] [<00000000ae6662ee>] update_process_times+0x4e/0x148
01: [ 2928.210734] [<00000000ae690c26>] tick_sched_timer+0x86/0x188
01: [ 2928.210741] [<00000000ae66989c>] __hrtimer_run_queues+0x84c/0x10b8
01: [ 2928.210748] [<00000000ae66c80a>] hrtimer_interrupt+0x38a/0x860
01: [ 2928.210758] [<00000000ae48dbf2>] do_IRQ+0x152/0x1c8
01: [ 2928.210767] [<00000000af5b00ea>] ext_int_handler+0x18e/0x194
01: [ 2928.210774] [<00000000ae5e332e>] arch_local_irq_restore+0x86/0xa0
01: [ 2928.210782] [<00000000af58da04>] lock_is_held_type+0xe4/0x130
01: [ 2928.210791] [<00000000ae63355a>] rcu_read_lock_held+0xba/0xd8
01: [ 2928.210799] [<00000000af0125fc>] xas_descend+0x244/0x2c8
01: [ 2928.210806] [<00000000af012754>] xas_load+0xd4/0x148
01: [ 2928.210812] [<00000000af014490>] xas_find+0x5d0/0x818
01: [ 2928.210822] [<00000000ae97e644>] do_madvise+0xd5c/0x1600
01: [ 2928.210828] [<00000000ae97f2d2>] __s390x_sys_madvise+0x72/0x98
01: [ 2928.210835] [<00000000af5af844>] system_call+0xdc/0x278
01: [ 2928.210841] 3 locks held by madvise06/62712:
01: [ 2928.216406] #0: 00000001437fca18 (&mm->mmap_lock){++++}-{3:3}, at: do_m
01: dvise+0x18c/0x1600
01: [ 2928.216430] #1: 00000000afbdd3e0 (rcu_read_lock){....}-{1:2}, at: do_mad
01: vise+0xe72/0x1600
01: [ 2928.216449] #2: 00000000afbe0818 (rcu_node_1){-.-.}-{2:2}, at: rcu_dump_
01: cpu_stacks+0xb2/0x2a8
