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From: Davidlohr Bueso <dave@stgolabs.net>
To: Peter Zijlstra <peterz@infradead.org>
Cc: David Howells <dhowells@redhat.com>,
	linux-afs@lists.infradead.org, Ingo Molnar <mingo@redhat.com>,
	Will Deacon <will@kernel.org>,
	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
	Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH] rxrpc: struct mutex cannot be used for rxrpc_call::user_mutex
Date: Wed, 18 Dec 2019 12:28:01 -0800	[thread overview]
Message-ID: <20191218202801.wokf6hcvbafmjnkd@linux-p48b> (raw)
In-Reply-To: <20191218190833.ufpxjrvin5jvp3m5@linux-p48b>

On Wed, 18 Dec 2019, Davidlohr Bueso wrote:

>On Wed, 18 Dec 2019, Peter Zijlstra wrote:
>
>>On Tue, Dec 17, 2019 at 03:32:00PM +0000, David Howells wrote:
>>>Standard kernel mutexes cannot be used in any way from interrupt or softirq
>>>context, so the user_mutex which manages access to a call cannot be a mutex
>>>since on a new call the mutex must start off locked and be unlocked within
>>>the softirq handler to prevent userspace interfering with a call we're
>>>setting up.
>>>
>>>Commit a0855d24fc22d49cdc25664fb224caee16998683 ("locking/mutex: Complain
>>>upon mutex API misuse in IRQ contexts") causes big warnings to be splashed
>>>in dmesg for each a new call that comes in from the server.
>>
>>FYI that patch has currently been reverted.
>>
>>commit c571b72e2b845ca0519670cb7c4b5fe5f56498a5 (tip/locking/urgent, tip/locking-urgent-for-linus)
>
>Will we ever want to re-add this warning (along with writer rwsems) at some point?
>
>It seems that having it actually prompts things getting fixed, as opposed to
>just sitting there forever borken (at least in -rt).

Hmm so fyi __crash_kexec() is another one, but can be called in hard-irq, and
it's extremely obvious that the trylock+unlock occurs in the same context.

It would be nice to automate this...

Thanks,
Davidlohr

  reply	other threads:[~2019-12-18 20:34 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-12-17 15:32 [PATCH] rxrpc: struct mutex cannot be used for rxrpc_call::user_mutex David Howells
2019-12-18 13:50 ` Peter Zijlstra
2019-12-18 19:08   ` Davidlohr Bueso
2019-12-18 20:28     ` Davidlohr Bueso [this message]
2019-12-19  9:05       ` Peter Zijlstra
2019-12-19 17:44         ` Davidlohr Bueso
2019-12-20 20:13           ` Peter Zijlstra
2019-12-18 20:39     ` Peter Zijlstra

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