linux-kernel - Re: [REPORT] Softlockups on PowerNV with upstream

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Message-ID: <tm2pvk7ylatmou2gjcctz4dzyw3rudw5hgqsiax3eoxfkvsrmz@vuzh3xuepq6n>
Date: Thu, 10 Apr 2025 17:52:59 +0530
From: Aditya Gupta <adityag@...ux.ibm.com>
To: Gavin Shan <gshan@...hat.com>
Cc: Oscar Salvador <osalvador@...e.de>, linux-mm@...ck.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Danilo Krummrich <dakr@...nel.org>,
        David Hildenbrand <david@...hat.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Mahesh J Salgaonkar <mahesh@...ux.ibm.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Sourabh Jain <sourabhjain@...ux.ibm.com>, linux-kernel@...r.kernel.org,
        Donet Tom <donettom@...ux.ibm.com>
Subject: Re: [REPORT] Softlockups on PowerNV with upstream

Cc +donet

On 25/04/10 07:44PM, Gavin Shan wrote:
> On 4/10/25 6:23 PM, Oscar Salvador wrote:
> > On Thu, Apr 10, 2025 at 03:35:19PM +1000, Gavin Shan wrote:
> > > Thanks, Oscar. You're correct that the overhead is introduced by for_each_present_section_nr().
> > > I already had the fix, working on IBM's Power9 machine, where the issue can be
> > > reproduced. Please see the attached patch.
> > > 
> > > I'm having most tests on ARM64 machine for the fix.
> > 
> > Looks good to me.
> > But we need a comment explaining why block_id is set to ULONG_MAX
> > at the beginning as this might not be obvious.
> > 
> > Also, do we need
> >   if (block_id != ULONG_MAX && memory_block_id(nr) == block_id) ?
> > 
> > Cannot just be
> > 
> >   if (memory_block_id(nr) == block_id) ?
> > 
> > AFAICS, the first time we loop through 'memory_block_id(nr) == ULONG_MAX'
> > will evaluate false and and we will set block_id afterwards.
> > 
> > Either way looks fine to me.
> > Another way I guess would be:
> > 
> 
> Yeah, we need to record the last handled block ID by @block_id. For the
> first time to register the block memory device in the loop, @block_id needs
> to be invalid (ULONG_MAX), bypassing the check of 'memory_block_id(nr) == block_id'.
> I will post the fix for review after Aditya confirms it works for him, with extra
> comment to explain why @block_id is initialized to ULONG_MAX.
> 
> Aditya, please have a try when you get a chance, thanks! I verified it on Power9
> machine where the issue exists and on one of my ARM64 machine.

I don't see any softlockups now with your patch as well as Oscar's patch.

Tested on PowerNV Power10.

Thanks for the quick replies Gavin.
- Aditya G

> 
> Thanks,
> Gavin
>