linux-kernel - [PATCH 4.4 35/49] dmaengine: pl330: fix double lock

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Date:   Thu,  7 Dec 2017 14:07:29 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Iago Abal <mail@...oabal.eu>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Vinod Koul <vinod.koul@...el.com>,
        Sasha Levin <alexander.levin@...izon.com>
Subject: [PATCH 4.4 35/49] dmaengine: pl330: fix double lock

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Iago Abal <mail@...oabal.eu>


[ Upstream commit 91539eb1fda2d530d3b268eef542c5414e54bf1a ]

The static bug finder EBA (http://www.iagoabal.eu/eba/) reported the
following double-lock bug:

    Double lock:
    1. spin_lock_irqsave(pch->lock, flags) at pl330_free_chan_resources:2236;
    2. call to function `pl330_release_channel' immediately after;
    3. call to function `dma_pl330_rqcb' in line 1753;
    4. spin_lock_irqsave(pch->lock, flags) at dma_pl330_rqcb:1505.

I have fixed it as suggested by Marek Szyprowski.

First, I have replaced `pch->lock' with `pl330->lock' in functions
`pl330_alloc_chan_resources' and `pl330_free_chan_resources'. This avoids
the double-lock by acquiring a different lock than `dma_pl330_rqcb'.

NOTE that, as a result, `pl330_free_chan_resources' executes
`list_splice_tail_init' on `pch->work_list' under lock `pl330->lock',
whereas in the rest of the code `pch->work_list' is protected by
`pch->lock'. I don't know if this may cause race conditions. Similarly
`pch->cyclic' is written by `pl330_alloc_chan_resources' under
`pl330->lock' but read by `pl330_tx_submit' under `pch->lock'.

Second, I have removed locking from `pl330_request_channel' and
`pl330_release_channel' functions. Function `pl330_request_channel' is
only called from `pl330_alloc_chan_resources', so the lock is already
held. Function `pl330_release_channel' is called from
`pl330_free_chan_resources', which already holds the lock, and from
`pl330_del'. Function `pl330_del' is called in an error path of
`pl330_probe' and at the end of `pl330_remove', but I assume that there
cannot be concurrent accesses to the protected data at those points.

Signed-off-by: Iago Abal <mail@...oabal.eu>
Reviewed-by: Marek Szyprowski <m.szyprowski@...sung.com>
Signed-off-by: Vinod Koul <vinod.koul@...el.com>
Signed-off-by: Sasha Levin <alexander.levin@...izon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 drivers/dma/pl330.c |   19 ++++++-------------
 1 file changed, 6 insertions(+), 13 deletions(-)

--- a/drivers/dma/pl330.c
+++ b/drivers/dma/pl330.c
@@ -1657,7 +1657,6 @@ static bool _chan_ns(const struct pl330_
 static struct pl330_thread *pl330_request_channel(struct pl330_dmac *pl330)
 {
 	struct pl330_thread *thrd = NULL;
-	unsigned long flags;
 	int chans, i;
 
 	if (pl330->state == DYING)
@@ -1665,8 +1664,6 @@ static struct pl330_thread *pl330_reques
 
 	chans = pl330->pcfg.num_chan;
 
-	spin_lock_irqsave(&pl330->lock, flags);
-
 	for (i = 0; i < chans; i++) {
 		thrd = &pl330->channels[i];
 		if ((thrd->free) && (!_manager_ns(thrd) ||
@@ -1684,8 +1681,6 @@ static struct pl330_thread *pl330_reques
 		thrd = NULL;
 	}
 
-	spin_unlock_irqrestore(&pl330->lock, flags);
-
 	return thrd;
 }
 
@@ -1703,7 +1698,6 @@ static inline void _free_event(struct pl
 static void pl330_release_channel(struct pl330_thread *thrd)
 {
 	struct pl330_dmac *pl330;
-	unsigned long flags;
 
 	if (!thrd || thrd->free)
 		return;
@@ -1715,10 +1709,8 @@ static void pl330_release_channel(struct
 
 	pl330 = thrd->dmac;
 
-	spin_lock_irqsave(&pl330->lock, flags);
 	_free_event(thrd, thrd->ev);
 	thrd->free = true;
-	spin_unlock_irqrestore(&pl330->lock, flags);
 }
 
 /* Initialize the structure for PL330 configuration, that can be used
@@ -2085,20 +2077,20 @@ static int pl330_alloc_chan_resources(st
 	struct pl330_dmac *pl330 = pch->dmac;
 	unsigned long flags;
 
-	spin_lock_irqsave(&pch->lock, flags);
+	spin_lock_irqsave(&pl330->lock, flags);
 
 	dma_cookie_init(chan);
 	pch->cyclic = false;
 
 	pch->thread = pl330_request_channel(pl330);
 	if (!pch->thread) {
-		spin_unlock_irqrestore(&pch->lock, flags);
+		spin_unlock_irqrestore(&pl330->lock, flags);
 		return -ENOMEM;
 	}
 
 	tasklet_init(&pch->task, pl330_tasklet, (unsigned long) pch);
 
-	spin_unlock_irqrestore(&pch->lock, flags);
+	spin_unlock_irqrestore(&pl330->lock, flags);
 
 	return 1;
 }
@@ -2201,12 +2193,13 @@ static int pl330_pause(struct dma_chan *
 static void pl330_free_chan_resources(struct dma_chan *chan)
 {
 	struct dma_pl330_chan *pch = to_pchan(chan);
+	struct pl330_dmac *pl330 = pch->dmac;
 	unsigned long flags;
 
 	tasklet_kill(&pch->task);
 
 	pm_runtime_get_sync(pch->dmac->ddma.dev);
-	spin_lock_irqsave(&pch->lock, flags);
+	spin_lock_irqsave(&pl330->lock, flags);
 
 	pl330_release_channel(pch->thread);
 	pch->thread = NULL;
@@ -2214,7 +2207,7 @@ static void pl330_free_chan_resources(st
 	if (pch->cyclic)
 		list_splice_tail_init(&pch->work_list, &pch->dmac->desc_pool);
 
-	spin_unlock_irqrestore(&pch->lock, flags);
+	spin_unlock_irqrestore(&pl330->lock, flags);
 	pm_runtime_mark_last_busy(pch->dmac->ddma.dev);
 	pm_runtime_put_autosuspend(pch->dmac->ddma.dev);
 }