Re: [PATCH v3 2/2] ARM: mm: protect show_pte() in do_DataAbort() fallback path

[Russell King <linux@armlinux.org.uk>]

On Fri, Jun 26, 2026 at 06:16:15PM +0800, Xie Yuanbin wrote:
> On Fri, 26 Jun 2026 15:30:48 +0800, Qi Xi wrote:
> > @@ -638,7 +638,10 @@ do_DataAbort(unsigned long addr, unsigned int fsr, struct pt_regs *regs)
> > 	pr_alert("8<--- cut here ---\n");
> > 	pr_alert("Unhandled fault: %s (0x%03x) at 0x%08lx\n",
> > 		inf->name, fsr, addr);
> > -	show_pte(KERN_ALERT, current->mm, addr);
> > +	if (mmap_read_trylock(current->mm)) {
> > +		show_pte(KERN_ALERT, current->mm, addr);
> > +		mmap_read_unlock(current->mm);
> > +	}
> 
> For kernel faults, `current->mm` maybe NULL, and
> `mmap_read_trylock(current->mm)` may cause a panic.
> Also, interrupts may be disabled here.
> 
> I suggest that waiting for this patch to be merged first:
> https://lore.kernel.org/20260625122612.43501-1-xieyuanbin1@huawei.com
> which make sure that interrupts are enabled here.

No, it doesn't ensure that.

show_pte() is also called from die_kernel_fault() and
__do_kernel_fault(), which can be from a path that has interrupts
disabled. See the comments in do_kernel_address_page_fault().

We are not "fixing" show_pte(), which is a diagnostic function when
things go wrong in the kernel, and is there to *try* to give us
information to diagnose what happened. It is *not* a function that
is used routinely in the kernel.

The fact it is racy with other CPUs may be a problem, but it isn't
a big problem because when it's called, the system is practically
dead anyway.

-- 
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