linux-kernel - RE: [PATCH V2 2/3] efi: Introduce efi_rts_workqueue and some infrastructure to invoke all efi_runtime

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Date:   Thu, 8 Mar 2018 17:05:44 +0000
From:   "Luck, Tony" <tony.luck@...el.com>
To:     Borislav Petkov <bp@...en8.de>,
        "Prakhya, Sai Praneeth" <sai.praneeth.prakhya@...el.com>
CC:     "linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Chun-Yi Lee <jlee@...e.com>, Will Deacon <will.deacon@....com>,
        "Hansen, Dave" <dave.hansen@...el.com>,
        Mark Rutland <mark.rutland@....com>,
        Bhupesh Sharma <bhsharma@...hat.com>,
        "Neri, Ricardo" <ricardo.neri@...el.com>,
        "Shankar, Ravi V" <ravi.v.shankar@...el.com>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        "Zijlstra, Peter" <peter.zijlstra@...el.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        "Williams, Dan J" <dan.j.williams@...el.com>
Subject: RE: [PATCH V2 2/3] efi: Introduce efi_rts_workqueue and some
 infrastructure to invoke all efi_runtime_services()

> "Hence, pstore calls efi_runtime_services() without using efi_rts_wq" -
> that doesn't sound like optimal design to me. I would try to shove them
> all through the workqueue - not have exceptions.

But pstore is trying to save the last gasp dying words from a kernel that
has paniced. There isn't any guarantee that work queue will run. I think
it is reasonable to have some special case to make sure that we do save
the information.  But perhaps that special case should be to have pstore
call directly into the guts of the EFI code and not worry about all these
fancy switches of "mm" etc.

This is true for the machine check logging case too, but the mitigation is
that the details of the error persist in the machine check banks across the
reset ... so all is not lost if the work queue isn't run here.

-Tony