[PATCH] nvme: pci: Fix NULL dereference when resetting NVMe SSD

[Rakesh Pandit <rakesh@tuxera.com>]

While doing IO if I reset NVMe SSD (model :Samsung MZVPV512HDGL-00000)
it doesn't work as expected also results in NULL point dereference and
system becomes unstable.

Device's access is successfully disabled and reset attempt does
successfully complete but restore isn't able to restore NVMe device
properly.  This patch at least makes the system stable.

[ 1619.130015] BUG: unable to handle kernel NULL pointer dereference at 00000000000001f8
[ 1619.130059] IP: nvme_reset+0x5/0x60
[ 1619.130075] PGD 0
[ 1619.130076] P4D 0

[ 1619.130103] Oops: 0000 [#1] SMP
[ 1619.130117] Modules linked in: rfcomm(E) fuse(E) nf_conntrack_netbios_ns(E)......
[ 1619.130403]  btrtl(E) ath(E) ......
[ 1619.130701]  usb_storage i2c_hid
[ 1619.130720] CPU: 0 PID: 31625 Comm: bash Tainted: G        W   E   4.11.0+ #3
[ 1619.130749] Hardware name: Acer Predator G9-591/Mustang_SLS, BIOS V1.10 03/03/2016
[ 1619.130780] task: ffff880163e48000 task.stack: ffffc900085c4000
[ 1619.130807] RIP: 0010:nvme_reset+0x5/0x60
[ 1619.130825] RSP: 0000:ffffc900085c7d68 EFLAGS: 00010246
[ 1619.130848] RAX: ffffffff815cc190 RBX: ffff8804aeaa1000 RCX: 0000000000000000
[ 1619.130877] RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
[ 1619.130904] RBP: ffffc900085c7d70 R08: 0000000000000002 R09: ffffc900085c7ca4
[ 1619.130934] R10: 0000000000000000 R11: 000000000000029e R12: ffff8804aeaa1100
[ 1619.130962] R13: 0000000000000002 R14: ffffc900085c7f18 R15: fffffffffffffff2
[ 1619.130994] FS:  00007f692d7cb700(0000) GS:ffff8804c1c00000(0000) knlGS:0000000000000000
[ 1619.131027] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 1619.131052] CR2: 00000000000001f8 CR3: 0000000164483000 CR4: 00000000003406f0
[ 1619.131083] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 1619.131113] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 1619.131144] Call Trace:
[ 1619.131159]  ? nvme_reset_notify+0x1a/0x30
[ 1619.131181]  pci_dev_restore+0x38/0x50
[ 1619.131199]  pci_reset_function+0x65/0x80
[ 1619.131218]  reset_store+0x54/0x80
[ 1619.131235]  dev_attr_store+0x18/0x30
[ 1619.131253]  sysfs_kf_write+0x37/0x40
[ 1619.131269]  kernfs_fop_write+0x110/0x1a0
[ 1619.131288]  __vfs_write+0x37/0x140
[ 1619.131306]  ? selinux_file_permission+0xd7/0x110
[ 1619.131328]  ? security_file_permission+0x3b/0xc0
[ 1619.131349]  vfs_write+0xb5/0x1a0
[ 1619.131366]  SyS_write+0x55/0xc0
[ 1619.131383]  entry_SYSCALL_64_fastpath+0x1a/0xa5
[ 1619.131405] RIP: 0033:0x7f692cec1c20
[ 1619.131421] RSP: 002b:00007ffeea27b938 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
[ 1619.131452] RAX: ffffffffffffffda RBX: 00007f692d18b5e0 RCX: 00007f692cec1c20
[ 1619.131481] RDX: 0000000000000002 RSI: 000055dcd896ccf0 RDI: 0000000000000001
[ 1619.131510] RBP: 0000000000000001 R08: 00007f692d18c740 R09: 00007f692d7cb700
[ 1619.131541] R10: 0000000000000073 R11: 0000000000000246 R12: 000055dcd89a3930
[ 1619.131571] R13: 0000000000000001 R14: 0000000000000000 R15: 0000000000000001
[ 1619.131601] Code: 84 00 00 00 00 00 0f 1f 44 00 00 55 89 f6 48 03
b7 40 ff ff ff 48 89 e5 48 8b 06 48 89 02 31 c0 5d c3 0f 1f 40 00 0f
1f 44 00 00 <48> 8b 87 f8 01 00 00 48 85 c0 74 49 48 8b 80 a0 01 00 00
a8 20
[ 1619.131708] RIP: nvme_reset+0x5/0x60 RSP: ffffc900085c7d68
[ 1619.131732] CR2: 00000000000001f8

Signed-off-by: Rakesh Pandit <rakesh@tuxera.com>
---

This is produce independent of separate issue under discussion
regarding resetting the device (system hang) and works well with or
without patch set "nvme: fix hang in path of removing disk".

 drivers/nvme/host/pci.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
index 0866f64..fce61eb 100644
--- a/drivers/nvme/host/pci.c
+++ b/drivers/nvme/host/pci.c
@@ -2159,6 +2159,11 @@ static void nvme_reset_notify(struct pci_dev *pdev, bool prepare)
 {
 	struct nvme_dev *dev = pci_get_drvdata(pdev);
 
+	if (!dev) {
+		pr_err("reset%s notification to nvme failed",
+				prepare ? " preparation" : "");
+		return;
+	}
 	if (prepare)
 		nvme_dev_disable(dev, false);
 	else
-- 
2.5.5