linux-kernel - Re: INFO: rcu detected stall in blkdev

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Date:   Sat, 5 May 2018 20:57:16 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:     syzbot 
        <syzbot+369c35474963daf8f8eea897ecf33cb6ad6c7ea2@...kaller.appspotmail.com>,
        axboe@...nel.dk, linux-block@...r.kernel.org,
        syzkaller-bugs@...glegroups.com, Jan Kara <jack@...e.cz>
Cc:     akpm@...ux-foundation.org, gregkh@...uxfoundation.org,
        hpa@...or.com, kstewart@...uxfoundation.org,
        linux-kernel@...r.kernel.org, mingo@...hat.com, npiggin@...il.com,
        pombredanne@...b.com, tglx@...utronix.de, x86@...nel.org
Subject: Re: INFO: rcu detected stall in blkdev_ioctl

If various stall reports regarding loop_set_fd() are hitting below sequence, a patch
was proposed at https://groups.google.com/d/msg/syzkaller-bugs/5pzXJ8yQFR0/vWeRytaQBAAJ .

----------
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <linux/loop.h>

int main(int argc, char *argv[])
{
        const int fd = open("/tmp/file", O_RDWR | O_CREAT | O_TRUNC, 0600);
        const int fd0 = open("/dev/loop0", O_RDONLY);
        const int fd1 = open("/dev/loop1", O_RDONLY);
        ioctl(fd0, LOOP_SET_FD, fd);
        ioctl(fd0, LOOP_CHANGE_FD, fd0);
        ioctl(fd1, LOOP_SET_FD, fd0);
        return 0;
}
----------