linux-kernel - regression: 4.13 cannot follow symlinks on some ext3 fs

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Message-ID: <20171123203330.GN2482@two.firstfloor.org>
Date:   Thu, 23 Nov 2017 12:33:30 -0800
From:   Andi Kleen <andi@...stfloor.org>
To:     tahsin@...gle.com, adilger@...ger.ca, tytso@....edu
Cc:     linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: regression: 4.13 cannot follow symlinks on some ext3 fs


Hi,

I have an older qemu VM image that i sometimes use for testing. It
stopped booting with 4.13-4.14 because it couldn't run init.  
It uses ext3 for the root file system.

I instrumented the code and found that it failed to follow the 
/lib/ld-linux.so.2 -> ld-2.3.6.so symlink for init's ELF interpreter. 

I bisected it to down to

commit 407cd7fb83c0ebabb490190e673d8c71ee7df97e (refs/bisect/bad)
Author: Tahsin Erdogan <tahsin@...gle.com>
Date:   Tue Jul 4 00:11:21 2017 -0400

    ext4: change fast symlink test to not rely on i_blocks

when I revert this commit 4.14 my VM runs fine again.

Dump of the inode in debugfs: 

debugfs:  Inode: 1767   Type: symlink    Mode:  0777   Flags: 0x0
Generation: 0
User:     0   Group:     0   Size: 11
File ACL: 0    Directory ACL: 0
Links: 1   Blockcount: 8
Fragment:  Address: 0    Number: 0    Size: 0
ctime: 0x45ad7ba0 -- Wed Jan 17 01:28:00 2007
atime: 0x5a164be5 -- Thu Nov 23 04:17:41 2017
mtime: 0x45ad7ba0 -- Wed Jan 17 01:28:00 2007
BLOCKS:
(0):11006
TOTAL: 1

-Andi