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

[Christoph Hellwig]

This looks odd.  The char_dev code should grab the reference to the
module in 

On Thu, Sep 03, 2020 at 07:39:29PM -0700, Chaitanya Kulkarni wrote:
> 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);

No need for a debug printk here..

Otherwise this looks good and should go to the front as it is a problem
even without the passthrough controller.