linux-kernel - Re: [PATCH v2] f2fs: Fix deadlock in shutdown ioctl

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Date:   Fri, 18 May 2018 13:09:53 +0530
From:   Sahitya Tummala <stummala@...eaurora.org>
To:     Jaegeuk Kim <jaegeuk@...nel.org>
Cc:     Chao Yu <yuchao0@...wei.com>,
        linux-f2fs-devel@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] f2fs: Fix deadlock in shutdown ioctl

On Thu, May 17, 2018 at 06:08:26PM -0700, Jaegeuk Kim wrote:
> 
> if (in == F2FS_GOING_DOWN_FULLSYNC) {
> 	sb = freeze_bdev();
> 	if (IS_ERR(sb))
> 		return PTR_ERR(sb);
> 	if (unlikely(!sb))
> 		return -EINVAL;
> }
> 
> ret = mnt_want_write_file();

It will be stuck/blocked here as freeze_bdev() now holds the write 
lock for all the cases including SB_FREEZE_WRITE. As freeze_bdev()
holds the write lock, I think f2fs_stop_checkpoint() should be safe
even without mnt_want_write_file().

I have posted v3 as per Chao's comments to exclude mnt_want_write_file()
for F2FS_GOING_DOWN_FULLSYNC case.
Please check and let me know if there are any further comments.

> ...
> switch() {
> case F2FS_GOING_DOWN_FULLSYNC:
> 	f2fs_stop_checkpoint();
> 	dhaw_bdev();
> 	break;
> ...
> }
> 
> drop:
> ...
> 
> 
--
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