Re: INFO: rcu detected stall in blkdev_ioctl

From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
To: syzbot
	<syzbot+369c35474963daf8f8eea897ecf33cb6ad6c7ea2@syzkaller.appspotmail.com>,
	axboe@kernel.dk, linux-block@vger.kernel.org,
	syzkaller-bugs@googlegroups.com, Jan Kara <jack@suse.cz>
Cc: akpm@linux-foundation.org, gregkh@linuxfoundation.org,
	hpa@zytor.com, kstewart@linuxfoundation.org,
	linux-kernel@vger.kernel.org, mingo@redhat.com,
	npiggin@gmail.com, pombredanne@nexb.com, tglx@linutronix.de,
	x86@kernel.org
Subject: Re: INFO: rcu detected stall in blkdev_ioctl
Date: Sat, 5 May 2018 20:57:16 +0900	[thread overview]
Message-ID: <00724984-6edd-d0df-4c51-53be8c330234@I-love.SAKURA.ne.jp> (raw)
In-Reply-To: <18608105-31d3-3d77-ccbb-a25bbe7e55e6@I-love.SAKURA.ne.jp>

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 .

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#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;
}
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