PCI: endpoint: pci-epf-test: NULL check dma channels before release

The fields dma_chan_tx and dma_chan_rx of the struct pci_epf_test can be
NULL even after epf initialization. Then it is prudent to check that
they have non-NULL values before releasing the channels. Add the checks
in pci_epf_test_clean_dma_chan().

Without the checks, NULL pointer dereferences happen and they can lead
to a kernel panic in some cases:

  Unable to handle kernel NULL pointer dereference at virtual address 0000000000000050
  Mem abort info:
    ESR = 0x0000000096000004
    EC = 0x25: DABT (current EL), IL = 32 bits
    SET = 0, FnV = 0
    EA = 0, S1PTW = 0
    FSC = 0x04: level 0 translation fault
  Data abort info:
    ISV = 0, ISS = 0x00000004, ISS2 = 0x00000000
    CM = 0, WnR = 0, TnD = 0, TagAccess = 0
    GCS = 0, Overlay = 0, DirtyBit = 0, Xs = 0
  user pgtable: 4k pages, 48-bit VAs, pgdp=000000011ab86000
  [0000000000000050] pgd=0000000000000000, p4d=0000000000000000
  Internal error: Oops: 0000000096000004 [#1]  SMP
  Modules linked in: pci_epf_test zram zsmalloc lzo_compress ramoops reed_solomon nvme_fabrics bridge stp llc usb_f_acm u_serial usb_f_rndis u_ether libcomposite snd_soc_tegra210_admaif snd_soc_tegra186_asrc snd_soc_tegra210_mvc snd_soc_tegra_pcm snd_soc_tegra210_sfc snd_soc_tegra210_ope snd_soc_tegra210_amx snd_soc_tegra210_mixer snd_soc_tegra210_i2s snd_soc_tegra210_adx snd_soc_simple_card_utils tegra_drm snd_soc_tegra210_ahub drm_dp_aux_bus cec snd_hda_codec_hdmi drm_display_helper snd_hda_tegra tegra_xudc drm_client_lib at24 snd_hda_codec drm_kms_helper tegra_se crypto_engine snd_hda_core pwm_tegra tegra_bpmp_thermal tpm_ftpm_tee ina3221 pwm_fan drm fuse ip_tables x_tables ipv6 r8169
  CPU: 2 UID: 0 PID: 127 Comm: irq/165-tegra_p Not tainted 6.16.3-tegra+ torvalds#156 PREEMPT
  Hardware name: NVIDIA NVIDIA Jetson Orin Nano Developer Kit/Jetson, BIOS 36.4.4-gcid-41062509 06/16/2025
  pstate: 60400009 (nZCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
  pc : dma_release_channel+0x2c/0x120
  lr : dma_release_channel+0x2c/0x120
  sp : ffff80008197bc90
  x29: ffff80008197bc90 x28: ffffc80c867353d0 x27: ffffc80c867320b0
  x26: ffff000089598680 x25: ffff000092bbca00 x24: ffff0000896075a0
  x23: ffff000089547308 x22: ffff000089547000 x21: ffff00009e14f800
  x20: ffffc80c88d18f50 x19: 0000000000000000 x18: 0000000000000000
  x17: ffff00008082bba0 x16: ffffc80c86fa1da8 x15: 0000000000000022
  x14: 0000000000000002 x13: 0000029f4ce9442c x12: 00000000000a8cc1
  x11: 0000000000000040 x10: ffffc80c88a06c60 x9 : ffffc80c86fa1dd4
  x8 : ffff0000804036e8 x7 : 0000000000000000 x6 : 0000000000000000
  x5 : ffff0000804036c0 x4 : 0000000000000000 x3 : 0000000000000000
  x2 : ffff000092bbca00 x1 : 0000000000000000 x0 : ffffc80c88d18f50
  Call trace:
   dma_release_channel+0x2c/0x120 (P)
   pci_epf_test_epc_deinit+0x94/0xc0 [pci_epf_test]
   pci_epc_deinit_notify+0x74/0xc0
   tegra_pcie_ep_pex_rst_irq+0x250/0x5d8
   irq_thread_fn+0x34/0xb8
   irq_thread+0x18c/0x2e8
   kthread+0x14c/0x210
   ret_from_fork+0x10/0x20
  Code: f000ebb4 913d4294 aa1403e0 942ac552 (b940526)
  ---[ end trace 0000000000000000 ]---
  Kernel panic - not syncing: Oops: Fatal exception

Fixes: 8353813 ("PCI: endpoint: Enable DMA tests for endpoints with DMA capabilities")
Fixes: 5ebf3fc ("PCI: endpoint: functions/pci-epf-test: Add DMA support to transfer data")
Cc: [email protected]
Signed-off-by: Shin'ichiro Kawasaki <[email protected]>
Reviewed-by: Damien Le Moal <[email protected]>
Reviewed-by: Krzysztof Wilczyński <[email protected]>

Author: kawasaki

drivers/pci/endpoint/functions/pci-epf-test.c

@@ -301,15 +301,20 @@ static void pci_epf_test_clean_dma_chan(struct pci_epf_test *epf_test)
 	if (!epf_test->dma_supported)
 		return;
 
-	dma_release_channel(epf_test->dma_chan_tx);
-	if (epf_test->dma_chan_tx == epf_test->dma_chan_rx) {
+	if (epf_test->dma_chan_tx) {
+		dma_release_channel(epf_test->dma_chan_tx);
+		if (epf_test->dma_chan_tx == epf_test->dma_chan_rx) {
+			epf_test->dma_chan_tx = NULL;
+			epf_test->dma_chan_rx = NULL;
+			return;
+		}
 		epf_test->dma_chan_tx = NULL;
-		epf_test->dma_chan_rx = NULL;
-		return;
 	}
 
-	dma_release_channel(epf_test->dma_chan_rx);
-	epf_test->dma_chan_rx = NULL;
+	if (epf_test->dma_chan_rx) {
+		dma_release_channel(epf_test->dma_chan_rx);
+		epf_test->dma_chan_rx = NULL;
+	}
 }
 
 static void pci_epf_test_print_rate(struct pci_epf_test *epf_test,