linux-kernel - Re: [RFC PATCH 0/6] Convert all tasklets to workqueues

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Date:	Sat, 30 Jun 2007 15:25:58 +0400
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Alexey Kuznetsov <kuznet@....inr.ac.ru>
Cc:	Ingo Molnar <mingo@...e.hu>, Jeff Garzik <jeff@...zik.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Christoph Hellwig <hch@...radead.org>,
	john stultz <johnstul@...ibm.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Dipankar Sarma <dipankar@...ibm.com>,
	"David S. Miller" <davem@...emloft.net>, matthew@....cx
Subject: Re: [RFC PATCH 0/6] Convert all tasklets to workqueues

On 06/29, Oleg Nesterov wrote:
>
> Suppose we have the tasklets T1 and T2, both are scheduled on the
> same CPU. T1 takes some spinlock LOCK.
> 
> Currently it is possible to do
> 
> 	spin_lock(LOCK);
> 	disable_tasklet(T2);
> 
> With this patch, the above code hangs.

I am stupid. Yes, flush_workqueue() is evil and should not be used, but
if we use workqueues, tasklet_disable() becomes might_sleep() anyway.
This is incompatible and unavoidable change.

grep, grep...

	net/bluetooth/hci_core.c:hci_rx_task()

		read_lock(&hci_task_lock)
		hci_event_packet()
			hci_num_comp_pkts_evt()
				tasklet_disable(&hdev->tx_task)

Oleg.

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