linux-kernel - Re: INFO: task hung in generic_file_write

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Message-ID: <275523c6-f750-44c2-a8a4-f3825eeab788@i-love.sakura.ne.jp>
Date:   Thu, 3 Jan 2019 01:07:25 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
To:     Jan Kara <jack@...e.cz>, Andrew Morton <akpm@...ux-foundation.org>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        syzbot <syzbot+9933e4476f365f5d5a1b@...kaller.appspotmail.com>,
        linux-mm@...ck.org, mgorman@...hsingularity.net,
        Michal Hocko <mhocko@...nel.org>, ak@...ux.intel.com,
        jlayton@...hat.com, linux-kernel@...r.kernel.org,
        mawilcox@...rosoft.com, syzkaller-bugs@...glegroups.com,
        tim.c.chen@...ux.intel.com,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: INFO: task hung in generic_file_write_iter

On 2019/01/02 23:40, Jan Kara wrote:
> I had a look into this and the only good explanation for this I have is
> that sb->s_blocksize is different from (1 << sb->s_bdev->bd_inode->i_blkbits).
> If that would happen, we'd get exactly the behavior syzkaller observes
> because grow_buffers() would populate different page than
> __find_get_block() then looks up.
> 
> However I don't see how that's possible since the filesystem has the block
> device open exclusively and blkdev_bszset() makes sure we also have
> exclusive access to the block device before changing the block device size.
> So changing block device block size after filesystem gets access to the
> device should be impossible. 
> 
> Anyway, could you perhaps add to your debug patch a dump of 'size' passed
> to __getblk_slow() and bdev->bd_inode->i_blkbits? That should tell us
> whether my theory is right or not. Thanks!
> 

OK. Andrew, will you add (or fold into) this change?

>From e6f334380ad2c87457bfc2a4058316c47f75824a Mon Sep 17 00:00:00 2001
From: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Date: Thu, 3 Jan 2019 01:03:35 +0900
Subject: [PATCH] fs/buffer.c: dump more info for __getblk_gfp() stall problem

We need to dump more variables on top of
"fs/buffer.c: add debug print for __getblk_gfp() stall problem".

Signed-off-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Cc: Jan Kara <jack@...e.cz>
---
 fs/buffer.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/fs/buffer.c b/fs/buffer.c
index 580fda0..a50acac 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -1066,9 +1066,14 @@ static sector_t blkdev_max_block(struct block_device *bdev, unsigned int size)
 #ifdef CONFIG_DEBUG_AID_FOR_SYZBOT
 		if (!time_after(jiffies, current->getblk_stamp + 3 * HZ))
 			continue;
-		printk(KERN_ERR "%s(%u): getblk(): executed=%x bh_count=%d bh_state=%lx\n",
+		printk(KERN_ERR "%s(%u): getblk(): executed=%x bh_count=%d bh_state=%lx "
+		       "bdev_super_blocksize=%lu size=%u "
+		       "bdev_super_blocksize_bits=%u bdev_inode_blkbits=%u\n",
 		       current->comm, current->pid, current->getblk_executed,
-		       current->getblk_bh_count, current->getblk_bh_state);
+		       current->getblk_bh_count, current->getblk_bh_state,
+		       bdev->bd_super->s_blocksize, size,
+		       bdev->bd_super->s_blocksize_bits,
+		       bdev->bd_inode->i_blkbits);
 		current->getblk_executed = 0;
 		current->getblk_bh_count = 0;
 		current->getblk_bh_state = 0;
-- 
1.8.3.1