[PATCH v2 1/3] nvme-hwmon: Return error on kzalloc failure

[Keith Busch]

On Fri, Sep 30, 2022 at 12:52:47PM +0300, Serge Semin wrote:
> On Thu, Sep 29, 2022 at 05:53:43PM -0600, Keith Busch wrote:
> > On Fri, Sep 30, 2022 at 01:46:46AM +0300, Serge Semin wrote:
> > > Inability to allocate a buffer is a critical error which shouldn't be
> > > tolerated since most likely the rest of the driver won't work correctly.
> > > Thus instead of returning the zero status let's return the -ENOMEM error
> > > if the nvme_hwmon_data structure instance couldn't be created.
> > 
> 
> > Nak for this one. The hwmon is not necessary for the rest of the driver to
> > function, so having the driver detach from the device seems a bit harsh.
> 
> Even if it is as you say, neither the method semantic nor the way it's
> called imply that. Any failures except the allocation one are
> perceived as erroneous.

This is called by nvme_init_ctrl_finish(), and returns the error to
nvme_reset_work() only if it's < 0, which indicates we can't go on and the
driver unbinds.

This particular condition for hwmon is not something that prevents us from
making forward progress.
 
> > The
> > driver can participate in memory reclaim, so failing on a low memory condition
> > can make matters worse.
> 
> Yes it can, so can many other places in the driver utilizing kmalloc
> with just GFP_KERNEL flag passed including on the same path as the
> nvme_hwmon_init() execution. Kmalloc will make sure the reclaim is
> either finished or executed in background anyway in all cases. 

This path is in the first initialization before we've set up a namespace that
can be used as a reclaim destination.

> Don't
> really see why memory allocation failure is less worse in this case
> than in many others in the same driver especially seeing as I said

The other initialization kmalloc's are required to make forward progress toward
setting up a namespace. This one is not required.