linux-kernel - Re: [PATCH v3 1/2] init/initramfs.c: do unpacking asynchronously

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Message-ID: <87pmv2g1v3.fsf@oc8242746057.ibm.com>
Date:   Wed, 28 Jul 2021 12:38:08 +0200
From:   Alexander Egorenkov <egorenar@...ux.ibm.com>
To:     Luis Chamberlain <mcgrof@...nel.org>,
        Bruno Goncalves <bgoncalv@...hat.com>
Cc:     Rasmus Villemoes <linux@...musvillemoes.dk>,
        akpm@...ux-foundation.org, bp@...en8.de, corbet@....net,
        gregkh@...uxfoundation.org, jeyu@...nel.org,
        linux-kernel@...r.kernel.org, ndesaulniers@...gle.com,
        torvalds@...ux-foundation.org, Dave Young <dyoung@...hat.com>
Subject: Re: [PATCH v3 1/2] init/initramfs.c: do unpacking asynchronously

Luis Chamberlain <mcgrof@...nel.org> writes:

> On Tue, Jul 27, 2021 at 09:31:54AM +0200, Bruno Goncalves wrote:
>> On Mon, Jul 26, 2021 at 1:46 PM Rasmus Villemoes
>> <linux@...musvillemoes.dk> wrote:
>> >
>> > On 24/07/2021 09.46, Alexander Egorenkov wrote:
>> > > Hello,
>> > >
>> > > since e7cb072eb988 ("init/initramfs.c: do unpacking asynchronously"), we
>> > > started seeing the following problem on s390 arch regularly:
>> > >
>> > > [    5.039734] wait_for_initramfs() called before rootfs_initcalls
>
> So some context here, which might help.
>
> The initramfs_cookie is initialized until a a rootfs_initcall() is
> called, in this case populate_rootfs(). The code is small, so might
> as well include it:
>
> static int __init populate_rootfs(void)
> {
> 	initramfs_cookie = async_schedule_domain(do_populate_rootfs, NULL,
> 						 &initramfs_domain);
> 	if (!initramfs_async)
> 		wait_for_initramfs();
> 	return 0;
> }                                                                               
> rootfs_initcall(populate_rootfs);
>
> The warning you see comes from a situation where a wait_for_initramfs()
> gets called but we haven't yet initialized initramfs_cookie.  There are
> only a few calls for wait_for_initramfs() in the kernel, and the only
> thing I can think of is that somehow s390 may rely on a usermode helper
> early on, but not every time.
>
> What umh calls does s390 issue?
>
>> Unfortunately, we haven't been able to find the root cause, but since
>> June 23rd we haven't hit this panic...
>> 
>> Btw, this panic we were hitting only when testing kernels from "scsi"
>> and "block" trees.
>
> Do you use drdb maybe?
>
>   Luis

You are right, it looks like wait_for_initramfs() is being triggered by drbg:

[    3.396467]  [<00000001f8d917e4>] call_usermodehelper_exec+0x44/0x1c8
[    3.396470]  [<00000001f8da5524>] __request_module+0x17c/0x3d0
[    3.396473]  [<00000001f93b4808>] crypto_alg_mod_lookup+0x228/0x290
[    3.396475]  [<00000001f93b4aae>] crypto_alloc_tfm_node+0x5e/0x158
[    3.396477]  [<00000001f93bbe14>] crypto_alloc_shash+0x34/0x40
[    3.396480]  [<00000001f93d2ee2>] drbg_init_hash_kernel+0x3a/0x100
[    3.396482]  [<00000001f93d306e>] drbg_alloc_state+0xc6/0x280
[    3.396484]  [<00000001f93d33d8>] drbg_kcapi_seed+0x1b0/0x310
[    3.396486]  [<00000001f93d1884>] crypto_rng_reset+0x5c/0xe0
[    3.396488]  [<00000001f93c1750>] alg_test_drbg+0x300/0x478
[    3.396490]  [<00000001f93c0934>] alg_test+0x304/0x530
[    3.396493]  [<00000001f93bedb8>] cryptomgr_test+0x68/0x70
[    3.396495]  [<00000001f8d9f40c>] kthread+0x14c/0x160
[    3.396497]  [<00000001f8d2af14>] __ret_from_fork+0x3c/0x58
[    3.396500]  [<00000001f984c86a>] ret_from_fork+0xa/0x30

Regards
Alex