Messages in this thread Patch in this message | | | Date | Fri, 30 Mar 2012 12:51:20 -0700 | From | Greg KH <> | Subject | [ 175/175] serial: sh-sci: fix a race of DMA submit_tx on transfer |
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3.3-stable review patch. If anyone has any objections, please let me know.
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From: Yoshii Takashi <takashi.yoshii.zj@renesas.com>
commit 49d4bcaddca977fffdea8b0b71f6e5da96dac78e upstream.
When DMA is enabled, sh-sci transfer begins with uart_start() sci_start_tx() if (cookie_tx < 0) schedule_work() Then, starts DMA when wq scheduled, -- (A) process_one_work() work_fn_rx() cookie_tx = desc->submit_tx() And finishes when DMA transfer ends, -- (B) sci_dma_tx_complete() async_tx_ack() cookie_tx = -EINVAL (possible another schedule_work())
This A to B sequence is not reentrant, since controlling variables (for example, cookie_tx above) are not queues nor lists. So, they must be invoked as A B A B..., otherwise results in kernel crash.
To ensure the sequence, sci_start_tx() seems to test if cookie_tx < 0 (represents "not used") to call schedule_work(). But cookie_tx will not be set (to a cookie, also means "used") until in the middle of work queue scheduled function work_fn_tx().
This gap between the test and set allows the breakage of the sequence under the very frequently call of uart_start(). Another gap between async_tx_ack() and another schedule_work() results in the same issue, too.
This patch introduces a new condition "cookie_tx == 0" just to mark it is "busy" and assign it within spin-locked region to fill the gaps.
Signed-off-by: Takashi Yoshii <takashi.yoshii.zj@renesas.com> Reviewed-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de> Signed-off-by: Paul Mundt <lethal@linux-sh.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
--- drivers/tty/serial/sh-sci.c | 15 ++++++++++----- 1 file changed, 10 insertions(+), 5 deletions(-)
--- a/drivers/tty/serial/sh-sci.c +++ b/drivers/tty/serial/sh-sci.c @@ -1229,17 +1229,20 @@ static void sci_dma_tx_complete(void *ar port->icount.tx += sg_dma_len(&s->sg_tx); async_tx_ack(s->desc_tx); - s->cookie_tx = -EINVAL; s->desc_tx = NULL; if (uart_circ_chars_pending(xmit) < WAKEUP_CHARS) uart_write_wakeup(port); if (!uart_circ_empty(xmit)) { + s->cookie_tx = 0; schedule_work(&s->work_tx); - } else if (port->type == PORT_SCIFA || port->type == PORT_SCIFB) { - u16 ctrl = sci_in(port, SCSCR); - sci_out(port, SCSCR, ctrl & ~SCSCR_TIE); + } else { + s->cookie_tx = -EINVAL; + if (port->type == PORT_SCIFA || port->type == PORT_SCIFB) { + u16 ctrl = sci_in(port, SCSCR); + sci_out(port, SCSCR, ctrl & ~SCSCR_TIE); + } } spin_unlock_irqrestore(&port->lock, flags); @@ -1501,8 +1504,10 @@ static void sci_start_tx(struct uart_por } if (s->chan_tx && !uart_circ_empty(&s->port.state->xmit) && - s->cookie_tx < 0) + s->cookie_tx < 0) { + s->cookie_tx = 0; schedule_work(&s->work_tx); + } #endif if (!s->chan_tx || port->type == PORT_SCIFA || port->type == PORT_SCIFB) {
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