linux-kernel - Re: [PATCH RFC v7 08/23] dept: Apply sdt_might_sleep_strong() to PG

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Message-Id: <1674272109-21876-1-git-send-email-byungchul.park@lge.com>
Date:   Sat, 21 Jan 2023 12:35:09 +0900
From:   Byungchul Park <byungchul.park@....com>
To:     hdanton@...a.com
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        torvalds@...ux-foundation.org, longman@...hat.com,
        penguin-kernel@...ove.SAKURA.ne.jp, max.byungchul.park@...il.com
Subject: Re: [PATCH RFC v7 08/23] dept: Apply sdt_might_sleep_strong() to PG_{locked,writeback} wait

Byungchul wrote:
> Hillf wrote:
> > On 9 Jan 2023 12:33:36 +0900 Byungchul Park <byungchul.park@....com>
> > > Makes Dept able to track dependencies by PG_{locked,writeback} waits.
> > > 
> > > Signed-off-by: Byungchul Park <byungchul.park@....com>
> > > ---
> > 
> > Hey Byungchul 
> 
> +cc max.byungchul.park@...il.com
> 
> Hi,
> 
> This email never reached to me.
> 
> > Is DEPT able to get deadlock reported for the syzbot report [1]?
> 
> DEPT can detect the case 100% *IF* the folio_trylock() is released
> within the same context since DEPT tracks folio_trylock(), folio_lock()
> and folio_unlock(), and it's definitely a deadlock.
> 
> But as we know, because folio_trylock() can be released by another
> context like irq, it might be either just a severe slowdown of the
> context triggering folio_unlock() or a literal deadlock where the
> context is involved. I dunno which one is the case.
> 
> In short, DEPT can detect this case too *IF* it's a literal deadlock,
> but it doesn't if it's just a slowdown. I'm planning to warn it even if
> there is a slowdown tho, not for now.
> 
> Let me reproduce the following issue. I will share the result.

Hi Hillf,

Can we talk about the DEPT report for the hang issue in here?

https://lore.kernel.org/lkml/1673235231-30302-1-git-send-email-byungchul.park@lge.com/T/#m458f4d5f3da06a28c7fbb39b392d05e4c016603b

Thanks,
	Byungchul

> > Hillf
> > 
> > [1] https://lore.kernel.org/lkml/6383cde5-cf4b-facf-6e07-1378a485657d@I-love.SAKURA.ne.jp/
> 
> 	Byungchul
>