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Date:	Thu, 20 Mar 2014 16:42:16 +0000
From:	Alan Cox <>
Cc:	Marcel Holtmann <>,
	Greg KH <>,
	Muralidharan Karicheri <>,,,
	Linux Kernel Mailing List <>
Subject: Re: hci_ldsic nested locking problem

On Thu, 2014-03-20 at 11:34 -0500, Felipe Balbi wrote:
> Hi,
> when 8250 driver calls uart_write_wakeup(), the tty port lock is already
> taken. hci_ldisc.c's implementation of ->write_wakeup() calls
> tty->ops->write() to actually send the characters, but that call will
> try to acquire the same port lock again.
> Looking at other line disciplines that looks like a bug in hci_ldisc.c.
> Am I correct to assume that ->write_wakeup() is supposed to *just*
> wakeup the bottom half so we handle ->write() in another context ?
> Is it legal to call tty->ops->write() from within ->write_wakeup() ?

It isn't because you might send all the bytes and go

				write wakeup

and recurse


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