From: Steven Rostedt <rostedt@goodmis.org>
To: Waiman Long <llong@redhat.com>
Cc: "Masami Hiramatsu (Google)" <mhiramat@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>, Will Deacon <will@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Boqun Feng <boqun.feng@gmail.com>,
Joel Granados <joel.granados@kernel.org>,
Anna Schumaker <anna.schumaker@oracle.com>,
Lance Yang <ioworker0@gmail.com>,
Kent Overstreet <kent.overstreet@linux.dev>,
Yongliang Gao <leonylgao@tencent.com>,
Tomasz Figa <tfiga@chromium.org>,
Sergey Senozhatsky <senozhatsky@chromium.org>,
linux-kernel@vger.kernel.org,
Linux Memory Management List <linux-mm@kvack.org>
Subject: Re: [PATCH 1/2] hung_task: Show the blocker task if the task is hung on mutex
Date: Wed, 19 Feb 2025 21:27:08 -0500 [thread overview]
Message-ID: <20250219212708.78b93a84@gandalf.local.home> (raw)
In-Reply-To: <9f9150b4-1cf5-4380-b431-419f70775a7d@redhat.com>
On Wed, 19 Feb 2025 21:15:08 -0500
Waiman Long <llong@redhat.com> wrote:
> Writer - setting them:
>
> WRITE_ONCE(lock)
> smp_wmb()
> WRITE_ONCE(type)
>
> Clearing them:
>
> WRITE_ONCE(type, 0)
> smp_wmb()
> WRITE_ONCE(lock, NULL)
>
> Reader:
>
> READ_ONCE(type)
> again:
> smp_rmb()
> READ_ONCE(lock)
> smp_rmb()
> if (READ_ONCE(type) != type)
> goto again
Do you really need the READ/WRITE_ONCE() with the memory barriers? From
what I understand, the compiler can't even assume what it read is the same
after passing a memory barrier like that. So there should be no reason it
can reread the memory location after a barrier.
-- Steve
next prev parent reply other threads:[~2025-02-20 2:26 UTC|newest]
Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-02-19 13:00 [PATCH 0/2] hung_task: Dump the blocking task stacktrace Masami Hiramatsu (Google)
2025-02-19 13:00 ` [PATCH 1/2] hung_task: Show the blocker task if the task is hung on mutex Masami Hiramatsu (Google)
2025-02-19 16:23 ` Steven Rostedt
2025-02-19 20:18 ` Waiman Long
2025-02-19 20:24 ` Steven Rostedt
2025-02-19 22:44 ` Waiman Long
2025-02-19 22:56 ` Masami Hiramatsu
2025-02-19 23:55 ` Steven Rostedt
2025-02-20 1:52 ` Lance Yang
2025-02-20 2:07 ` Masami Hiramatsu
2025-02-20 2:21 ` Waiman Long
2025-02-20 2:23 ` Steven Rostedt
2025-02-20 1:36 ` Waiman Long
2025-02-20 1:41 ` Steven Rostedt
2025-02-20 2:15 ` Waiman Long
2025-02-20 2:27 ` Steven Rostedt [this message]
2025-02-20 3:29 ` Waiman Long
2025-02-20 2:59 ` Masami Hiramatsu
2025-02-20 3:37 ` Waiman Long
2025-02-20 9:29 ` Masami Hiramatsu
2025-02-20 13:28 ` Waiman Long
2025-02-20 2:40 ` Masami Hiramatsu
2025-02-20 3:11 ` Steven Rostedt
2025-02-20 13:13 ` Waiman Long
2025-02-20 16:30 ` Steven Rostedt
2025-02-19 23:09 ` Masami Hiramatsu
2025-02-19 23:58 ` Steven Rostedt
2025-02-20 2:08 ` Masami Hiramatsu
2025-02-20 2:25 ` Waiman Long
2025-02-20 1:40 ` Waiman Long
2025-02-20 2:45 ` Sergey Senozhatsky
2025-02-20 4:19 ` Sergey Senozhatsky
2025-02-20 3:46 ` Sergey Senozhatsky
2025-02-20 3:49 ` Waiman Long
2025-02-20 9:25 ` Masami Hiramatsu
2025-02-19 13:00 ` [PATCH 2/2] samples: Add hung_task detector mutex blocking sample Masami Hiramatsu (Google)
2025-02-19 13:33 ` [PATCH 0/2] hung_task: Dump the blocking task stacktrace Lance Yang
2025-02-19 15:02 ` Lance Yang
2025-02-19 20:20 ` Waiman Long
2025-02-20 1:27 ` Lance Yang
2025-02-20 14:18 ` Masami Hiramatsu
2025-02-20 14:22 ` Waiman Long
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