This fixes a race condition where the channel resources could be freed
before the ISR had finished running resulting in a NULL pointer
reference from the ISR.
[ 167.148934] Unable to handle kernel NULL pointer dereference at virtual address 00000000
[ 167.157051] pgd = ffff80003c641000
[ 167.160449] [00000000] *pgd=000000007c507003, *pud=000000007c4ff003, *pmd=0000000000000000
[ 167.168719] Internal error: Oops: 96000046 [#1] PREEMPT SMP
[ 167.174289] Modules linked in:
[ 167.177348] CPU: 3 PID: 10547 Comm: dma_ioctl Not tainted 4.11.0-rc1-00001-g8d92afddc2f6633a #73
[ 167.186131] Hardware name: Renesas Salvator-X board based on r8a7795 (DT)
[ 167.192917] task: ffff80003a411a00 task.stack: ffff80003bcd4000
[ 167.198850] PC is at rcar_dmac_chan_prep_sg+0xe0/0x400
[ 167.203985] LR is at rcar_dmac_chan_prep_sg+0x48/0x400
Based of previous work by:
Hiroyuki Yokoyama <hiroyuki.yokoyama.vx@xxxxxxxxxxx>.
Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@xxxxxxxxxxxx>
---
drivers/dma/sh/rcar-dmac.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/drivers/dma/sh/rcar-dmac.c b/drivers/dma/sh/rcar-dmac.c
index 4b90deb40d559bed..0ec63600ebcc3a27 100644
--- a/drivers/dma/sh/rcar-dmac.c
+++ b/drivers/dma/sh/rcar-dmac.c
@@ -998,7 +998,11 @@ static void rcar_dmac_free_chan_resources(struct dma_chan *chan)
rcar_dmac_chan_halt(rchan);
spin_unlock_irq(&rchan->lock);
- /* Now no new interrupts will occur */
+ /*
+ * Now no new interrupts will occur, but one might already be
+ * running. Wait for it to finish before freeing resources.
+ */
+ synchronize_irq(rchan->irq);
if (rchan->mid_rid >= 0) {
/* The caller is holding dma_list_mutex */
--
2.12.0
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