From: Tejun Heo <tj@kernel.org>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: sooraj <sooraj20636@gmail.com>,
linux-mm@kvack.org, linux-block@vger.kernel.org
Subject: Re: [PATCH] mm/bdi: fix race between cgwb_create and conflicting blkcg associations
Date: Tue, 28 Jan 2025 10:48:32 -1000 [thread overview]
Message-ID: <Z5lCoLgRTOwDZxNW@slm.duckdns.org> (raw)
In-Reply-To: <20250127165311.f51b98290b548aff1df92a81@linux-foundation.org>
Hello,
On Mon, Jan 27, 2025 at 04:53:11PM -0800, Andrew Morton wrote:
> On Tue, 28 Jan 2025 02:52:50 -0500 sooraj <sooraj20636@gmail.com> wrote:
>
> > Ensure cgwb (cgroup writeback) structures are uniquely associated with a
> > memcg-blkcg pair to prevent inconsistencies when concurrent cgwb_create
> > calls race. This resolves a scenario where two threads creating cgwbs
> > for the same memory cgroup (memcg) but different I/O control groups (blkcg)
> > could insert conflicting entries.
> >
> > The fix rechecks for existing cgwbs under the cgwb_lock spinlock after
> > initial creation. If a conflicting cgwb (same memcg, different blkcg) is
> > found, it is killed before inserting the new entry. This guarantees a
> > 1:1 relationship between memcg-blkcg pairs and their cgwbs, preserving
> > system invariants.
I'm a bit confused. Radix tree doesn't allow two entries to be inserted on
the same key and the tree is keyed by memcg_id. Wouldn't that automatically
guarantee 1:1 relationship?
Thanks.
--
tejun
prev parent reply other threads:[~2025-01-28 20:48 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-01-28 7:52 sooraj
2025-01-28 0:53 ` Andrew Morton
2025-01-28 20:48 ` Tejun Heo [this message]
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