Re: hci_ldsic nested locking problem

From: Peter Hurley
Date: Thu Mar 20 2014 - 13:31:55 EST

[ +cc Huang Shijie ]

On 03/20/2014 01:16 PM, Felipe Balbi wrote:
On Thu, Mar 20, 2014 at 04:42:16PM +0000, Alan Cox wrote:
On Thu, 2014-03-20 at 11:34 -0500, Felipe Balbi wrote:

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

cool, so there really is a bug in hci_ldisc. Marcel, any tips on how do
you want this to be sorted out ?

hci_uart_tx_wakeup() should perform the I/O as work.
FWIW, this was reported by Huang Shijie back on Dec 6.

I'd fix it but I have no way to test it.

Peter Hurley
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