scsi: sd: Fix crashes in sd_resume_runtime()

After commit ed4246d3 ("scsi: sd: REQUEST SENSE for
BLIST_IGN_MEDIA_CHANGE devices in runtime_resume()"), the following crash
was observed.

static int sd_resume_runtime(struct device *dev)
{
        struct scsi_disk *sdkp = dev_get_drvdata(dev);
        struct scsi_device *sdp = sdkp->device; // sdkp == NULL and crash

        if (sdp->ignore_media_change) {
	...
}

It is possible for sdkp to be NULL in sd_resume_runtime(). To fix this
crash, follow sd_resume() to test if sdkp is NULL before dereferencing it.

Crash:
[    4.695171][  T151] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000008
[    4.696591][  T151] Mem abort info:
[    4.697919][  T151]   ESR = 0x96000005
[    4.699692][  T151]   EC = 0x25: DABT (current EL), IL = 32 bits
[    4.701990][  T151]   SET = 0, FnV = 0
[    4.702513][  T151]   EA = 0, S1PTW = 0
[    4.704431][  T151]   FSC = 0x05: level 1 translation fault
[    4.705254][  T151] Data abort info:
[    4.705806][  T151]   ISV = 0, ISS = 0x00000005
[    4.706484][  T151]   CM = 0, WnR = 0
[    4.707048][  T151] [0000000000000008] user address but active_mm is swapper
[    4.710577][  T151] Internal error: Oops: 96000005 [#1] PREEMPT SMP
[    4.832361][  T151] Kernel Offset: 0x12acc80000 from 0xffffffc010000000
[    4.833254][  T151] PHYS_OFFSET: 0x40000000
[    4.833814][  T151] pstate: 80400005 (Nzcv daif +PAN -UAO)
[    4.834546][  T151] pc : sd_resume_runtime+0x20/0x14c
[    4.835227][  T151] lr : scsi_runtime_resume+0x84/0xe4
[    4.835916][  T151] sp : ffffffc0110db8d0
[    4.836450][  T151] x29: ffffffc0110db8d0 x28: 0000000000000001
[    4.837258][  T151] x27: ffffff80c0bd1ac0 x26: ffffff80c0bd1ad0
[    4.838063][  T151] x25: ffffff80cea7e448 x24: ffffffd2bf961000
[    4.838867][  T151] x23: ffffffd2be69f838 x22: ffffffd2bd9dfb4c
[    4.839670][  T151] x21: 0000000000000000 x20: ffffff80cea7e000
[    4.840474][  T151] x19: ffffff80cea7e260 x18: ffffffc0110dd078
[    4.841277][  T151] x17: 00000000658783d9 x16: 0000000051469dac
[    4.842081][  T151] x15: 00000000b87f6327 x14: 0000000068fd680d
[    4.842885][  T151] x13: ffffff80c0bd2470 x12: ffffffd2bfa7f5f0
[    4.843688][  T151] x11: 0000000000000078 x10: 0000000000000001
[    4.844492][  T151] x9 : 00000000000000b1 x8 : ffffffd2be69f88c
[    4.845295][  T151] x7 : ffffffd2bd9e0e5c x6 : 0000000000000000
[    4.846099][  T151] x5 : 0000000000000080 x4 : 0000000000000001
[    4.846902][  T151] x3 : 68fd680dfe4ebe5e x2 : 0000000000000003
[    4.847706][  T151] x1 : ffffffd2bf7f9380 x0 : ffffff80cea7e260
[    4.856708][  T151]  die+0x16c/0x59c
[    4.857191][  T151]  __do_kernel_fault+0x1e8/0x210
[    4.857833][  T151]  do_page_fault+0xa4/0x654
[    4.858418][  T151]  do_translation_fault+0x6c/0x1b0
[    4.859083][  T151]  do_mem_abort+0x68/0x10c
[    4.859655][  T151]  el1_abort+0x40/0x64
[    4.860182][  T151]  el1h_64_sync_handler+0x54/0x88
[    4.860834][  T151]  el1h_64_sync+0x7c/0x80
[    4.861395][  T151]  sd_resume_runtime+0x20/0x14c
[    4.862025][  T151]  scsi_runtime_resume+0x84/0xe4
[    4.862667][  T151]  __rpm_callback+0x1f4/0x8cc
[    4.863275][  T151]  rpm_resume+0x7e8/0xaa4
[    4.863836][  T151]  __pm_runtime_resume+0xa0/0x110
[    4.864489][  T151]  sd_probe+0x30/0x428
[    4.865016][  T151]  really_probe+0x14c/0x500
[    4.865602][  T151]  __driver_probe_device+0xb4/0x18c
[    4.866278][  T151]  driver_probe_device+0x60/0x2c4
[    4.866931][  T151]  __device_attach_driver+0x228/0x2bc
[    4.867630][  T151]  __device_attach_async_helper+0x154/0x21c
[    4.868398][  T151]  async_run_entry_fn+0x5c/0x1c4
[    4.869038][  T151]  process_one_work+0x3ac/0x590
[    4.869670][  T151]  worker_thread+0x320/0x758
[    4.870265][  T151]  kthread+0x2e8/0x35c
[    4.870792][  T151]  ret_from_fork+0x10/0x20

Link: https://lore.kernel.org/r/20211015074654.19615-1-miles.chen@mediatek.com
Fixes: ed4246d3 ("scsi: sd: REQUEST SENSE for BLIST_IGN_MEDIA_CHANGE devices in runtime_resume()")
Cc: Stanley Chu <stanley.chu@mediatek.com>
Reviewed-by: Martin Kepplinger <martin.kepplinger@puri.sm>
Reviewed-by: Stanley Chu <stanley.chu@mediatek.com>
Signed-off-by: Miles Chen <miles.chen@mediatek.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/sd.c

@@ -3683,7 +3683,12 @@ static int sd_resume(struct device *dev)
 static int sd_resume_runtime(struct device *dev)
 {
 	struct scsi_disk *sdkp = dev_get_drvdata(dev);
-	struct scsi_device *sdp = sdkp->device;
+	struct scsi_device *sdp;
+
+	if (!sdkp)	/* E.g.: runtime resume at the start of sd_probe() */
+		return 0;
+
+	sdp = sdkp->device;
 
 	if (sdp->ignore_media_change) {
 		/* clear the device's sense data */