Re: [uml-devel] uml does not work with initrd=file

[<sg...@ao...>]

On Sun, 15 Jan 2017, Thomas Meyer wrote:

> Am 15. Januar 2017 13:16:22 MEZ schrieb sg...@ao...:
>> Hi,
>>
>> there seems to be a problem with usermode linux when started
>> with an initial ramdisk (argument initrd=file). Here is what
>> happens:
>>
>> ------------------------------------
>>
>> Locating the bottom of the address space ... 0x1000
>> Locating the top of the address space ... Checking that ptrace can
>> change system call numbers...0xc0000000
>> Core dump limits :
>> 	soft - 0
>> 	hard - NONE
>> OK
>> Checking syscall emulation patch for ptrace...OK
>> Checking advanced syscall emulation patch for ptrace...OK
>> Checking environment variables for a tempdir...none found
>> Checking if /dev/shm is on tmpfs...OK
>> Checking PROT_EXEC mmap in /dev/shm...OK
>> Adding 8470528 bytes to physical memory to account for exec-shield gap
>> kmsg_dump:
>> <1>bootmem alloc of 140 bytes failed!
>> <0>Kernel panic - not syncing: Out of memory
>> <4>CPU: 0 PID: 0 Comm: swapper Not tainted 4.9.0-um #3
>> <6>Stack:
>> <4> 081eb922 081eb922 0822d547 00000000 08222000 00000000 0817fe48
>> 00000000
>> <4> 0822bf6c 080bd1a7 00000007 0829c600 081f113d 0822bfbc 082220fc
>> 00000000
>> <4> 00000000 00000000 0805393d 081f113d 0000008c 0804c88e 0000008c
>> 00000080
>> <6>Call Trace:
>> <6> [<0805cffb>] ?
>> <4>show_stack+0x9d/0x157
>> <6> [<0817fe48>] ?
>> <4>dump_stack+0x23/0x2b
>> <6> [<080bd1a7>] ?
>> <4>panic+0x9e/0x1b4
>> <6> [<0805393d>] ?
>> <4>__alloc_bootmem+0x3f/0x43
>> <6> [<0804c88e>] ?
>> <4>read_initrd+0x6a/0x101
>> <6> [<08096fa5>] ?
>> <4>kmsg_dump_register+0x37/0x65
>> <6> [<0805e8a9>] ?
>> <4>uml_finishsetup+0x27/0x3b
>> <6>
>>
>> ---------------------------------
>>
>>
>> Function read_initrd() calls alloc_bootmem(), but at this point
>> memory hasn't been initialized yet.
>>
>> A quick solution is to move uml_postsetup() (the function
>> that calls read_initrd()) right after the memory has been
>> initialized. This may be wrong since uml_postsetup() may call
>> other functions besides read_initrd(), but worked for me:
>> the initial ramdisk is loaded and init run.
>>
>>
>> --- linux-4.9.0/arch/um/kernel/um_arch.c	2016-12-11 20:17:54.000000000
>> +0100
>> +++ linux-4.9.0-um/arch/um/kernel/um_arch.c	2017-01-15
>> 11:16:32.000000000 +0100
>> @@ -231,7 +231,7 @@
>>  	atomic_notifier_chain_register(&panic_notifier_list,
>>  				       &panic_exit_notifier);
>>
>> -	uml_postsetup();
>> +	// uml_postsetup();
>>
>>  	new_thread_handler();
>>  }
>> @@ -340,6 +340,7 @@
>>  {
>>  	stack_protections((unsigned long) &init_thread_info);
>>  	setup_physmem(uml_physmem, uml_reserved, physmem_size, highmem);
>> +	uml_postsetup();
>>  	mem_total_pages(physmem_size, iomem_size, highmem);
>>
>>  	paging_init();
>>
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>
> Hi,
>
> I don't think this is correct. How much memory do you assign your uml instance?
>

I tried:

vmlinux initrd=initrd.gz
vmlinux initrd=initrd.gz mem=10M
vmlinux initrd=initrd.gz mem=100M

the result is the same. ulimit -m gives "unlimited". With the same 
settings, uml had no problem booting from a romfs filesystem without
initrd.

> Your initial ramdisk is probably bigger than your assigned memory size?
>

I suspected something like this, so I tried with smaller and smaller
ramdisks.

The log above is for an initrd.gz of 140 bytes (just a text
file with 10 letters in it, cpio'd and compressed). Of course the
kernel would not find /init in it, but it never arrives at that
point. I enclose initrd.gz, and also .config, just in case it
could be useful.

> With kind regards
> Thomas
>