Re: Hang when swapping huge=within_size tmpfs from zram

[Baolin Wang <baolin.wang@linux.alibaba.com>]

Hi Alex,

On 2025/2/5 09:23, Alex Xu (Hello71) wrote:
> Hi all,
> 
> On 6.14-rc1, I found that creating a lot of files in tmpfs then deleting
> them reliably hangs when tmpfs is mounted with huge=within_size, and it
> is swapped out to zram (zstd/zsmalloc/no backing dev). I bisected this
> to acd7ccb284b "mm: shmem: add large folio support for tmpfs".
> 
> When the issue occurs, rm uses 100% CPU, cannot be killed, and has no
> output in /proc/pid/stack or wchan. Eventually, an RCU stall is
> detected:

Thanks for your report. Let me try to reproduce the issue locally and 
see what happens.

> rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
> rcu: 	Tasks blocked on level-0 rcu_node (CPUs 0-11): P25160
> rcu: 	(detected by 10, t=2102 jiffies, g=532677, q=4997 ncpus=12)
> task:rm              state:R  running task     stack:0     pid:25160 tgid:25160 ppid:24309  task_flags:0x400000 flags:0x00004004
> Call Trace:
>   <TASK>
>   ? __schedule+0x388/0x1000
>   ? kmem_cache_free.part.0+0x23d/0x280
>   ? sysvec_apic_timer_interrupt+0xa/0x80
>   ? asm_sysvec_apic_timer_interrupt+0x16/0x20
>   ? xas_load+0x12/0xc0
>   ? xas_load+0x8/0xc0
>   ? xas_find+0x144/0x190
>   ? find_lock_entries+0x75/0x260
>   ? shmem_undo_range+0xe6/0x5f0
>   ? shmem_evict_inode+0xe4/0x230
>   ? mtree_erase+0x7e/0xe0
>   ? inode_set_ctime_current+0x2e/0x1f0
>   ? evict+0xe9/0x260
>   ? _atomic_dec_and_lock+0x31/0x50
>   ? do_unlinkat+0x270/0x2b0
>   ? __x64_sys_unlinkat+0x30/0x50
>   ? do_syscall_64+0x37/0xe0
>   ? entry_SYSCALL_64_after_hwframe+0x50/0x58
>   </TASK>
> 
> Let me know what information is needed to further troubleshoot this
> issue.
> 
> Thanks,
> Alex.