Re: [syzbot] [mm?] WARNING in ep_write_iter

[Alan Stern]

On Mon, Aug 17, 2026 at 02:45:19PM -0400, Zi Yan wrote:
> On 17 Aug 2026, at 11:37, Alan Stern wrote:
> >>> Regardless, if it is important to let kernel developers know that their
> >>> code is doing something wrong, why not make the WARN conditional on
> >>> CONFIG_EXPERT or something similar?  In other words, prevent it from
> >>> crashing production systems.
> >
> > You didn't respond to this.
> 
> I do not get your argument here. Why does this WARN need to be conditional
> on CONFIG_EXPERT? What makes it special? Or you mean you want all WARNs
> to be conditional CONFIG_EXPERT?

This may be a moot point now, but I'll answer the questions anyway.

This WARN should be conditional on something indicating that the kernel 
is meant for testing rather than production (not necessarily 
CONFIG_EXPERT but something like it) because it does not indicate that 
an operation has failed badly enough to leave the kernel in a 
dangerously unstable state.  Rather, it indicates that a programmer has 
tried to do something that can't possibly succeed.  The result should 
not be dangerous because the caller should always check kmalloc()'s 
return value.  If the caller is unable to recover from a memory 
allocation failure then it is the caller's responsibility to WARN, not 
kmalloc()'s.

The same is true for all other WARN statements.  If they merely indicate 
a programming infelicity and not a dangerous failure then they should 
not fire in production kernels.

Alan Stern