linux-kernel - Re: [PATCH 2/4] swait: add the missing killable swaits

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Date:   Thu, 29 Jun 2017 10:40:46 -0700
From:   Davidlohr Bueso <dave@...olabs.net>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Greg KH <gregkh@...uxfoundation.org>,
        "Luis R. Rodriguez" <mcgrof@...nel.org>, mfuzzey@...keon.com,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Daniel Wagner <wagi@...om.org>,
        David Woodhouse <dwmw2@...radead.org>,
        jewalt@...innovations.com, rafal@...ecki.pl,
        Arend Van Spriel <arend.vanspriel@...adcom.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        "Li, Yi" <yi1.li@...ux.intel.com>, atull@...nel.org,
        Moritz Fischer <moritz.fischer@...us.com>,
        Petr Mladek <pmladek@...e.com>,
        Johannes Berg <johannes.berg@...el.com>,
        Emmanuel Grumbach <emmanuel.grumbach@...el.com>,
        "Coelho, Luciano" <luciano.coelho@...el.com>,
        Kalle Valo <kvalo@...eaurora.org>,
        Andrew Lutomirski <luto@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        "AKASHI, Takahiro" <takahiro.akashi@...aro.org>,
        David Howells <dhowells@...hat.com>,
        Peter Jones <pjones@...hat.com>,
        Hans de Goede <hdegoede@...hat.com>,
        Alan Cox <alan@...ux.intel.com>, Theodore Ts'o <tytso@....edu>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        Paul Gortmaker <paul.gortmaker@...driver.com>,
        Marcelo Tosatti <mtosatti@...hat.com>,
        Matthew Wilcox <mawilcox@...rosoft.com>,
        Linux API <linux-api@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "stable # 4 . 6" <stable@...r.kernel.org>
Subject: Re: [PATCH 2/4] swait: add the missing killable swaits

On Thu, 29 Jun 2017, Linus Torvalds wrote:

>Well, I'd actually say it the other way around: swait should not be
>used in general, only in _very_ particular pieces of code that
>actually explicitly need the odd swait semantics.
>
>swait uses special locking and has odd semantics that are not at all
>the same as the default wait queue ones. It should not be used without
>very strong reasons (and honestly, the only strong enough reason seems
>to be "RT").
>
>The special locking means that swait doesn't do DEBUG_LOCK_ALLOC, but
>it also means that it doesn't even work in all contexts.
>
>So "swake_up()" does surprising things (only wake up one - that's what
>caused a firmware loading bug), and "swake_up_all()" has magic rules
>about interrupt disabling.
>
>The thing is simply a collection of small hacks and should NOT be used
>in general.

For all the above, what do you think of my 'sswait' proposal?

Thanks,
Davidlohr