linux-kernel - Re: [PATCH] scsi: sd: unregister device if device_add_disk() failed in sd

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Message-ID: <ZbfkZxMVpVI97zmk@bombadil.infradead.org>
Date: Mon, 29 Jan 2024 09:46:15 -0800
From: Luis Chamberlain <mcgrof@...nel.org>
To: Yu Kuai <yukuai1@...weicloud.com>
Cc: linan666@...weicloud.com, jejb@...ux.ibm.com,
	martin.petersen@...cle.com, linux-scsi@...r.kernel.org,
	linux-kernel@...r.kernel.org, linan122@...wei.com,
	yi.zhang@...wei.com, houtao1@...wei.com, yangerkun@...wei.com,
	"yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [PATCH] scsi: sd: unregister device if device_add_disk() failed
 in sd_probe()

On Fri, Dec 22, 2023 at 04:27:16PM +0800, Yu Kuai wrote:
> Hi,
> 
> 在 2023/12/22 14:49, Luis Chamberlain 写道:
> > On Fri, Dec 08, 2023 at 04:23:35PM +0800, linan666@...weicloud.com wrote:
> > > From: Li Nan <linan122@...wei.com>
> > > 
> > > "if device_add() succeeds, you should call device_del() when you want to
> > > get rid of it."
> > > 
> > > In sd_probe(), device_add_disk() fails when device_add() has already
> > > succeeded, so change put_device() to device_unregister() to ensure device
> > > resources are released.
> > > 
> > > Fixes: 2a7a891f4c40 ("scsi: sd: Add error handling support for add_disk()")
> > > Signed-off-by: Li Nan <linan122@...wei.com>
> > 
> > Nacked-by: Luis Chamberlain <mcgrof@...nel.org>
> > 
> > > ---
> > >   drivers/scsi/sd.c | 2 +-
> > >   1 file changed, 1 insertion(+), 1 deletion(-)
> > > 
> > > diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
> > > index 542a4bbb21bc..d81cbeee06eb 100644
> > > --- a/drivers/scsi/sd.c
> > > +++ b/drivers/scsi/sd.c
> > > @@ -3736,7 +3736,7 @@ static int sd_probe(struct device *dev)
> > >   	error = device_add_disk(dev, gd, NULL);
> > >   	if (error) {
> > > -		put_device(&sdkp->disk_dev);
> > > +		device_unregister(&sdkp->disk_dev);
> > >   		put_disk(gd);
> > >   		goto out;
> > >   	}
> > 
> > This is incorrect, device_unregister() calls:
> > 
> > void device_unregister(struct device *dev)
> > {
> > 	pr_debug("device: '%s': %s\n", dev_name(dev), __func__);
> > 	device_del(dev);
> > 	put_device(dev);
> > }
> > 
> > So you're adding what you believe to be a correct missing device_del().
> > But what you missed is that if device_add_disk() fails then device_add()
> > did not succeed because the new code we have in the kernel *today* unwinds
> > this for us now.
> 
> I'm confused here, there are two device here, one is 'sdkp->disk_dev',
> one is gendisk->part0->bd_device, and the order in which they
> initialize:
> 
> sd_probe
> device_add(&sdkp->disk_dev) -> succeed
> device_add_disk -> failed, and device_add(bd_device) did not succeed
> put_device(&sdkp->disk_dev) -> device_del is missed
> 
> I don't see that if device_add_disk() fail, device_del() for
> 'sdkp->disk_dev'is called from anywhere. Do I missing anything?

Ah then the fix is still incorrect and the commit log should
describe that this is for another device.

How about this instead?

>From c3f6e03f4a82aa253b6c487a293dcd576393b606 Mon Sep 17 00:00:00 2001
From: Luis Chamberlain <mcgrof@...nel.org>
Date: Mon, 29 Jan 2024 09:25:18 -0800
Subject: [PATCH] sd: remove extra put_device() for extra scsi device

The sd driver first device_add() its own device, and later use
device_add_disk() with another device. When we added error handling
for device_add_disk() we now call put_disk() and that will trigger
disk_release() when the refcount is 0. That will end up calling
the block driver's disk->fops->free_disk() if one is defined. The
sd driver has scsi_disk_free_disk() as its free_disk() and that
does the proper put_device(&sdkp->disk_dev) for us so we should not
need to call it, however we are left still missing the device_del()
for it.

While at it, unwind with scsi_autopm_put_device(sdp) *prior* to
putting to device as we do in sd_remove().

Reported-by: Li Nan <linan122@...wei.com>
Reported-by: Yu Kuai <yukuai1@...weicloud.com>
Fixes: 2a7a891f4c40 ("scsi: sd: Add error handling support for add_disk()")
Signed-off-by: Luis Chamberlain <mcgrof@...nel.org>
---
 drivers/scsi/sd.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
index 7f949adbadfd..6475a3c947f8 100644
--- a/drivers/scsi/sd.c
+++ b/drivers/scsi/sd.c
@@ -3693,8 +3693,9 @@ static int sd_probe(struct device *dev)
 
 	error = device_add(&sdkp->disk_dev);
 	if (error) {
+		scsi_autopm_put_device(sdp);
 		put_device(&sdkp->disk_dev);
-		goto out;
+		return error;
 	}
 
 	dev_set_drvdata(dev, sdkp);
@@ -3734,9 +3735,10 @@ static int sd_probe(struct device *dev)
 
 	error = device_add_disk(dev, gd, NULL);
 	if (error) {
-		put_device(&sdkp->disk_dev);
+		scsi_autopm_put_device(sdp);
+		device_del(&sdkp->disk_dev);
 		put_disk(gd);
-		goto out;
+		return error;
 	}
 
 	if (sdkp->security) {
-- 
2.42.0