linux-ext4 - Re: [RESEND PATCH v10 08/25] dept: Apply sdt_might_sleep_{start,end}() to PG

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20230821043744.GA73328@system.software.com>
Date:   Mon, 21 Aug 2023 13:37:44 +0900
From:   Byungchul Park <byungchul@...com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     linux-kernel@...r.kernel.org, kernel_team@...ynix.com,
        torvalds@...ux-foundation.org, damien.lemoal@...nsource.wdc.com,
        linux-ide@...r.kernel.org, adilger.kernel@...ger.ca,
        linux-ext4@...r.kernel.org, mingo@...hat.com, peterz@...radead.org,
        will@...nel.org, tglx@...utronix.de, rostedt@...dmis.org,
        joel@...lfernandes.org, sashal@...nel.org, daniel.vetter@...ll.ch,
        duyuyang@...il.com, johannes.berg@...el.com, tj@...nel.org,
        tytso@....edu, david@...morbit.com, amir73il@...il.com,
        gregkh@...uxfoundation.org, kernel-team@....com,
        linux-mm@...ck.org, akpm@...ux-foundation.org, mhocko@...nel.org,
        minchan@...nel.org, hannes@...xchg.org, vdavydov.dev@...il.com,
        sj@...nel.org, jglisse@...hat.com, dennis@...nel.org, cl@...ux.com,
        penberg@...nel.org, rientjes@...gle.com, vbabka@...e.cz,
        ngupta@...are.org, linux-block@...r.kernel.org,
        josef@...icpanda.com, linux-fsdevel@...r.kernel.org,
        viro@...iv.linux.org.uk, jack@...e.cz, jlayton@...nel.org,
        dan.j.williams@...el.com, hch@...radead.org, djwong@...nel.org,
        dri-devel@...ts.freedesktop.org, rodrigosiqueiramelo@...il.com,
        melissa.srw@...il.com, hamohammed.sa@...il.com,
        42.hyeyoo@...il.com, chris.p.wilson@...el.com,
        gwan-gyeong.mun@...el.com, max.byungchul.park@...il.com,
        boqun.feng@...il.com, longman@...hat.com, hdanton@...a.com,
        her0gyugyu@...il.com
Subject: Re: [RESEND PATCH v10 08/25] dept: Apply
 sdt_might_sleep_{start,end}() to PG_{locked,writeback} wait

On Mon, Aug 21, 2023 at 05:09:44AM +0100, Matthew Wilcox wrote:
> On Mon, Aug 21, 2023 at 12:46:20PM +0900, Byungchul Park wrote:
> > @@ -1219,6 +1220,9 @@ static inline bool folio_trylock_flag(struct folio *folio, int bit_nr,
> >  /* How many times do we accept lock stealing from under a waiter? */
> >  int sysctl_page_lock_unfairness = 5;
> >  
> > +static struct dept_map __maybe_unused PG_locked_map = DEPT_MAP_INITIALIZER(PG_locked_map, NULL);
> > +static struct dept_map __maybe_unused PG_writeback_map = DEPT_MAP_INITIALIZER(PG_writeback_map, NULL);
> 
> Hmm, why are these "maybe unused"?  *digs*.  Ah.  Because
> sdt_might_sleep_start() becomes a no-op macro if DEPT is disabled.
> 
> OK, the right way to handle this is
> 
> #ifdef CONFIG_DEPT
> #define DEPT_MAP(name)	static struct dept_map name = \
> 		DEPT_MAP_INITIALIZER(name, NULL)
> #else
> #define DEPT_MAP(name)	/* */
> #endif
> 
> And now DEPT takes up no space if disabled.

Currently:

   #if !defined(CONFIG_DEPT)
   struct dept_map { }; 
   #endif

So I think it doesn't take space at all. Do you think I still need to
introduce e.g. DEPT_MAP()? Then I will. Thank you!

	Byungchul

> /* */; is a somewhat unusual thing to see, but since this must work at
> top level, we can't use "do { } while (0)" like we usually do.  Given
> where else this is likely to be used, i don't think it's going to be
> a problem ...