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From:   chenguanyou <chenguanyou9338@gmail.com>
To:     akpm@linux-foundation.org
Cc:     chenguanyou9338@gmail.com, chenguanyou@xiaomi.com,
        gpiccoli@canonical.com, keescook@chromium.org,
        linux-kernel@vger.kernel.org, lukas.bulwahn@gmail.com,
        mhocko@suse.com, vbabka@suse.cz
Subject: Re:[PATCH v2] hungtask: add filter kthread
Date:   Sat,  7 Aug 2021 21:16:00 +0800
Message-Id: <20210807131600.27742-1-chenguanyou@xiaomi.com>
In-Reply-To: <20210805164328.58213d35e45d81c363b2135e@linux-foundation.org>
References: <20210805164328.58213d35e45d81c363b2135e@linux-foundation.org>
Precedence: bulk

> Please explain this point in more detail?

In my work,the rootcause of more deadlocks often occurs in user threads.

exp:
PID: 711 TASK: ffffffc13eb71d00 CPU: 0 COMMAND: "sensors@2.0-ser"
#0 [ffffff80251cbcb0] __switch_to at ffffff80080866c4
#1 [ffffff80251cbd20] __schedule at ffffff80090c0940
#2 [ffffff80251cbd80] schedule_preempt_disabled at ffffff80090c0e4c
#3 [ffffff80251cbde0] __mutex_lock at ffffff80090c2e58
#4 [ffffff80251cbe40] __mutex_lock_slowpath at ffffff80090c1f78
#5 [ffffff80251cbe50] mutex_lock at ffffff80090c1f60
#6 [ffffff80251cbe60] __fdget_pos at ffffff800829ac84
#7 [ffffff80251cbe90] sys_write at ffffff8008270550
#8 [ffffff80251cbff0] el0_svc_naked at ffffff8008083fbc

PID: 843 TASK: ffffffc135832b80 CPU: 2 COMMAND: "sensors@2.0-ser"
#0 [ffffff802554bb30] __switch_to at ffffff80080866c4
#1 [ffffff802554bba0] __schedule at ffffff80090c0940
#2 [ffffff802554bc00] schedule at ffffff80090c0d54
#3 [ffffff802554bc50] xxx_sensor_show at ffffff8008bc043c
#4 [ffffff802554bc80] dev_attr_show at ffffff8008668ce0
#5 [ffffff802554bca0] sysfs_kf_seq_show at ffffff8008314e04
#6 [ffffff802554bce0] kernfs_seq_show at ffffff8008314314
#7 [ffffff802554bd10] seq_read at ffffff80082a250c
#8 [ffffff802554bd70] kernfs_fop_read at ffffff80083135b8
#9 [ffffff802554be20] __vfs_read at ffffff800826fcc0
#10 [ffffff802554be40] vfs_read at ffffff800826ff08
#11 [ffffff802554be90] sys_read at ffffff80082704c4
#12 [ffffff802554bff0] el0_svc_naked at ffffff8008083fbc

The rootcause is deadlock caused by using same fd, and 843's file ops is block type;
If we want to trigger panic in the first time through hungtask,
must be avoid detect kernel threads on some platforms("mediatek"),
because they("kernel threads") cause misjudgments.

Guanyou.Chen