linux-kernel - Re: [BUG, bisect] hang when copying large file to disc

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Date:	Sat, 31 Jan 2015 21:02:30 -0500
From:	Theodore Ts'o <tytso@....edu>
To:	Jeremiah Mahler <jmmahler@...il.com>, linux-kernel@...r.kernel.org
Subject: Re: [BUG, bisect] hang when copying large file to disc

On Fri, Jan 30, 2015 at 07:40:51PM -0800, Jeremiah Mahler wrote:
> 
> If a large file (> 1 GB) is transferred from a USB stick or a mmc
> to an local disc (using ext4), it will proceed normally until it
> has transferred approximately 600 MB.  Then the speed will drop off
> to zero and the terminal performing the operation will usually
> hang.  And sometimes other terminals will hang as well.  A reboot
> is required to get the system working again.
> 
>   mount /dev/sdb1 /mnt
>   pv /mnt/large_file > large_file_out
>   (... ~600 MB ... hang)
> 
> I have performed a bisect and found that commit ef39794651347 introduced
> the bug.  This commit is present in the latest -next 20150130.

Thanks for the bug report.  I was able to reproduce the problem, and
found the problem.  Unfortunately I accidentally introduce this in my
most recent patchset.  I'll fix it up, but here is the patch until I
get the a new version pushed out.

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 82c2984..0046861 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -1192,9 +1192,9 @@ void __mark_inode_dirty(struct inode *inode, int flags)
 
 		trace_writeback_dirty_inode(inode, flags);
 	}
-	dirtytime = flags & I_DIRTY_TIME;
 	if (flags & I_DIRTY_INODE)
 		flags &= ~I_DIRTY_TIME;
+	dirtytime = flags & I_DIRTY_TIME;
 
 	/*
 	 * Paired with smp_mb() in __writeback_single_inode() for the

	   	       		   			      	  - Ted
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