[PATCH 3/3] nvme-core: fix nvme module ref count Oops

[Chaitanya Kulkarni]

In the passthru controller enable path current code doesn't take the
reference to the passthru ctrl module. Which produces following Oops :-

Entering kdb (current=0xffff8887f8290000, pid 3128) on processor 30 Oops: (null)
due to oops @ 0xffffffffa01019ad
CPU: 30 PID: 3128 Comm: bash Tainted: G        W  OE     5.8.0-rc4nvme-5.9+ #35
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.12.0-59-gc9ba5276e321-prebuilt.qemu.4
RIP: 0010:nvme_free_ctrl+0x234/0x285 [nvme_core]
Code: 57 10 a0 e8 73 bf 02 e1 ba 3d 11 00 00 48 c7 c6 98 33 10 a0 48 c7 c7 1d 57 10 a0 e8 5b bf 02 e1 8
RSP: 0018:ffffc90001d63de0 EFLAGS: 00010246
RAX: ffffffffa05c0440 RBX: ffff8888119e45a0 RCX: 0000000000000000
RDX: 0000000000000000 RSI: ffff8888177e9550 RDI: ffff8888119e43b0
RBP: ffff8887d4768000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: ffffc90001d63c90 R12: ffff8888119e43b0
R13: ffff8888119e5108 R14: dead000000000100 R15: ffff8888119e5108
FS:  00007f1ef27b0740(0000) GS:ffff888817600000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffffffa05c0470 CR3: 00000007f6bee000 CR4: 00000000003406e0
Call Trace:
 device_release+0x27/0x80
 kobject_put+0x98/0x170
 nvmet_passthru_ctrl_disable+0x4a/0x70 [nvmet]
 nvmet_passthru_enable_store+0x4c/0x90 [nvmet]
 configfs_write_file+0xe6/0x150
 vfs_write+0xba/0x1e0
 ksys_write+0x5f/0xe0
 do_syscall_64+0x52/0xb0
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x7f1ef1eb2840
Code: Bad RIP value.
RSP: 002b:00007fffdbff0eb8 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 0000000000000002 RCX: 00007f1ef1eb2840
RDX: 0000000000000002 RSI: 00007f1ef27d2000 RDI: 0000000000000001
RBP: 00007f1ef27d2000 R08: 000000000000000a R09: 00007f1ef27b0740
R10: 0000000000000001 R11: 0000000000000246 R12: 00007f1ef2186400
R13: 0000000000000002 R14: 0000000000000001 R15: 0000000000000000

We fix that by taking a module ref count in nvme_dev_open() and release
that ref count in nvme_dev_release() atomically with ctrl get/put
respectively.

Signed-off-by: Chaitanya Kulkarni <chaitanya.kulkarni at wdc.com>
---
 drivers/nvme/host/core.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index a1707afcb710..8445293c74e3 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -3263,6 +3263,12 @@ static int nvme_dev_open(struct inode *inode, struct file *file)
 
 	file->private_data = ctrl;
 	nvme_get_ctrl(ctrl);
+	if (!try_module_get(ctrl->ops->module)) {
+		pr_err("try_module_get failed for cntlid 0x%x\n", ctrl->cntlid);
+		nvme_put_ctrl(ctrl);
+		return -EINVAL;
+	}
+
 	return 0;
 }
 
@@ -3271,6 +3277,7 @@ static int nvme_dev_release(struct inode *inode, struct file *file)
 	struct nvme_ctrl *ctrl =
 		container_of(inode->i_cdev, struct nvme_ctrl, cdev);
 
+	module_put(ctrl->ops->module);
 	nvme_put_ctrl(ctrl);
 	return 0;
 }
-- 
2.22.1