linux-kernel - Re: [PATCH] zram: Using GFP_ATOMIC instead of GFP_KERNEL to allocate bitmap memory in backing_dev

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Message-ID: <20231201153956.GB404241@google.com>
Date:   Sat, 2 Dec 2023 00:39:56 +0900
From:   Sergey Senozhatsky <senozhatsky@...omium.org>
To:     Dongyun Liu <dongyun.liu3@...il.com>
Cc:     minchan@...nel.org, senozhatsky@...omium.org, axboe@...nel.dk,
        linux-kernel@...r.kernel.org, linux-block@...r.kernel.org,
        lincheng.yang@...nssion.com, jiajun.ling@...nssion.com,
        ldys2014@...mail.com, Dongyun Liu <dongyun.liu@...nssion.com>
Subject: Re: [PATCH] zram: Using GFP_ATOMIC instead of GFP_KERNEL to allocate
 bitmap memory in backing_dev_store

On (23/11/30 23:20), Dongyun Liu wrote:
> INFO: task init:331 blocked for more than 120 seconds.  "echo 0 >
> /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> task:init   state:D stack:    0 pid:    1 ppid:     0 flags:0x04000000
> Call trace:
>   __switch_to+0x244/0x4e4
>   __schedule+0x5bc/0xc48
>   schedule+0x80/0x164
>   rwsem_down_read_slowpath+0x4fc/0xf9c
>   __down_read+0x140/0x188
>   down_read+0x14/0x24
>   try_wakeup_wbd_thread+0x78/0x1ec [zram]
>   __zram_bvec_write+0x720/0x878 [zram]
>   zram_bvec_rw+0xa8/0x234 [zram]
>   zram_submit_bio+0x16c/0x268 [zram]
>   submit_bio_noacct+0x128/0x3c8
>   submit_bio+0x1cc/0x3d0
>   __swap_writepage+0x5c4/0xd4c
>   swap_writepage+0x130/0x158
>   pageout+0x1f4/0x478
>   shrink_page_list+0x9b4/0x1eb8
>   shrink_inactive_list+0x2f4/0xaa8
>   shrink_lruvec+0x184/0x340
>   shrink_node_memcgs+0x84/0x3a0
>   shrink_node+0x2c4/0x6c4
>   shrink_zones+0x16c/0x29c
>   do_try_to_free_pages+0xe4/0x2b4
>   try_to_free_pages+0x388/0x7b4
>   __alloc_pages_direct_reclaim+0x88/0x278
>   __alloc_pages_slowpath+0x4ec/0xf6c
>   __alloc_pages_nodemask+0x1f4/0x3dc
>   kmalloc_order+0x54/0x338
>   kmalloc_order_trace+0x34/0x1bc
>   __kmalloc+0x5e8/0x9c0
>   kvmalloc_node+0xa8/0x264
>   backing_dev_store+0x1a4/0x818 [zram]
>   dev_attr_store+0x38/0x8c
>   sysfs_kf_write+0x64/0xc4

Hmm, I'm not really following this backtrace. Backing device
configuration is only possible on un-initialized zram device.
If it's uninitialized, then why is it being used for swapout
later in the call stack?