On 23.04.2012 13:19, Ian Kent wrote:
> On Sun, 2012-04-22 at 19:22 +0400, Michael Tokarev wrote:
>> This is JFYI for now, I only diagnozed the issue but had
>> no time to see what's going on.
>>
>> The short story is that with 3.0.24 and later kernels,
>> 32bit autofs stopped working on 64bit kernels, while
>> it worked before just fine.
>>
>> The userspace is of version 5.0.4. Platform is x86.
>>
>> The sympthoms of the issue is that automount daemon,
>> on every access to a (not yet mounted) autofs mount
>> point, stalls forever, with the process trying to
>> access it stalling forever too -- this is why the
>> system didn't reboot, -- it stayed on an attempt to
>> access one of automount subdirs, somewhere in the
>> middle.
This is what happens with 3.0.24+:
[pid 15207] read(4, "\5\0\0\0\3\0\0\0\2\0\0\0\35\0\0\0@\17\246\3\0\0\0\0\350\3\0\0\350\3\0\0"..., 304) = 300
[pid 15207] read(4, <unfinished ...> -- forever.
It wants to read 304 bytes, but kernel only supplies 300
bytes.
$ file /usr/sbin/automount
/usr/sbin/automount: ELF 32-bit LSB shared object, Intel 80386, version 1 (SYSV), dynamically linked (uses shared libs), for GNU/Linux 2.6.18, stripped
$ uname -a
Linux gandalf 3.0.0-amd64 #3.0.27 SMP Tue Apr 3 16:23:45 MSK 2012 x86_64 GNU/Linux
This is a32744d4abae24572eff7269bc17895c41bd0085
"autofs: work around unhappy compat problem on x86-64",
included in 3.0.24:
+static noinline size_t autofs_v5_packet_size(struct autofs_sb_info *sbi)
+{
+ size_t pktsz = sizeof(struct autofs_v5_packet);
+#if defined(CONFIG_X86_64) && defined(CONFIG_COMPAT)
+ if (sbi->compat_daemon > 0)
+ pktsz -= 4;
+#endif
+ return pktsz;
+}
+
"End result: the "packed" size of the structure is 300 bytes: 4-byte, but
not 8-byte aligned.
As a result, despite all the fields being in the same place on all
architectures, sizeof() will round up that size to 304 bytes on
architectures that have 8-byte alignment for u64."
So I'm not sure how it worked before this change (from the
description of the patch it looks like it should not work).
But it definitely worked for me, and this patch broke it
for me.
The autofs userspace is from Debian package.
> It looks like a change from kernel 3.3 has been back ported to earlier
> kernels. I'll need to work out which versions and prepare a patch.
Should 3.3 work? As far as I can see, it includes the
same change (which has been backported!), so it may have
the same _issue_...
Thanks,
/mjt
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