Add exception protection processing for vd in axi_chan_handle_err function

Since there is no protection for vd, a kernel panic will be
triggered here in exceptional cases.

You can refer to the processing of axi_chan_block_xfer_complete function

The triggered kernel panic is as follows:

[   67.848444] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000060
[   67.848447] Mem abort info:
[   67.848449]   ESR = 0x96000004
[   67.848451]   EC = 0x25: DABT (current EL), IL = 32 bits
[   67.848454]   SET = 0, FnV = 0
[   67.848456]   EA = 0, S1PTW = 0
[   67.848458] Data abort info:
[   67.848460]   ISV = 0, ISS = 0x00000004
[   67.848462]   CM = 0, WnR = 0
[   67.848465] user pgtable: 4k pages, 48-bit VAs, pgdp=00000800c4c0b000
[   67.848468] [0000000000000060] pgd=0000000000000000, p4d=0000000000000000
[   67.848472] Internal error: Oops: 96000004 [#1] SMP
[   67.848475] Modules linked in: dmatest
[   67.848479] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.10.100-emu_x2rc+ #11
[   67.848483] pstate: 62000085 (nZCv daIf -PAN -UAO +TCO BTYPE=--)
[   67.848487] pc : axi_chan_handle_err+0xc4/0x230
[   67.848491] lr : axi_chan_handle_err+0x30/0x230
[   67.848493] sp : ffff0803fe55ae50
[   67.848495] x29: ffff0803fe55ae50 x28: ffff800011212200
[   67.848500] x27: ffff0800c42c0080 x26: ffff0800c097c080
[   67.848504] x25: ffff800010d33880 x24: ffff80001139d850
[   67.848508] x23: ffff0800c097c168 x22: 0000000000000000
[   67.848512] x21: 0000000000000080 x20: 0000000000002000
[   67.848517] x19: ffff0800c097c080 x18: 0000000000000000
[   67.848521] x17: 0000000000000000 x16: 0000000000000000
[   67.848525] x15: 0000000000000000 x14: 0000000000000000
[   67.848529] x13: 0000000000000000 x12: 0000000000000040
[   67.848533] x11: ffff0800c0400248 x10: ffff0800c040024a
[   67.848538] x9 : ffff800010576cd4 x8 : ffff0800c0400270
[   67.848542] x7 : 0000000000000000 x6 : ffff0800c04003e0
[   67.848546] x5 : ffff0800c0400248 x4 : ffff0800c4294480
[   67.848550] x3 : dead000000000100 x2 : dead000000000122
[   67.848555] x1 : 0000000000000100 x0 : ffff0800c097c168
[   67.848559] Call trace:
[   67.848562]  axi_chan_handle_err+0xc4/0x230
[   67.848566]  dw_axi_dma_interrupt+0xf4/0x590
[   67.848569]  __handle_irq_event_percpu+0x60/0x220
[   67.848573]  handle_irq_event+0x64/0x120
[   67.848576]  handle_fasteoi_irq+0xc4/0x220
[   67.848580]  __handle_domain_irq+0x80/0xe0
[   67.848583]  gic_handle_irq+0xc0/0x138
[   67.848585]  el1_irq+0xc8/0x180
[   67.848588]  arch_cpu_idle+0x14/0x2c
[   67.848591]  default_idle_call+0x40/0x16c
[   67.848594]  do_idle+0x1f0/0x250
[   67.848597]  cpu_startup_entry+0x2c/0x60
[   67.848600]  rest_init+0xc0/0xcc
[   67.848603]  arch_call_rest_init+0x14/0x1c
[   67.848606]  start_kernel+0x4cc/0x500
[   67.848610] Code: eb0002ff 9a9f12d6 f2fbd5a2 f2fbd5a3 (a94602c1)
[   67.848613] ---[ end trace 585a97036f88203a ]---

Signed-off-by: Shawn.Shao <shawn.shao@jaguarmicro.com>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20230112055802.1764-1-shawn.shao@jaguarmicro.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>

Author: Shawn.Shao

drivers/dma/dw-axi-dmac/dw-axi-dmac-platform.c

@@ -1018,6 +1018,11 @@ static noinline void axi_chan_handle_err(struct axi_dma_chan *chan, u32 status)
 
 	/* The bad descriptor currently is in the head of vc list */
 	vd = vchan_next_desc(&chan->vc);
+	if (!vd) {
+		dev_err(chan2dev(chan), "BUG: %s, IRQ with no descriptors\n",
+			axi_chan_name(chan));
+		goto out;
+	}
 	/* Remove the completed descriptor from issued list */
 	list_del(&vd->node);
 
@@ -1032,6 +1037,7 @@ static noinline void axi_chan_handle_err(struct axi_dma_chan *chan, u32 status)
 	/* Try to restart the controller */
 	axi_chan_start_first_queued(chan);
 
+out:
 	spin_unlock_irqrestore(&chan->vc.lock, flags);
 }