Re: [PATCH] Revert "mm/vunmap: add cond_resched() in vunmap_pmd_range"

[Matthew Wilcox]

On Thu, Nov 05, 2020 at 09:02:49AM -0800, Minchan Kim wrote:
> This reverts commit e47110e90584a22e9980510b00d0dfad3a83354e.
> 
> While I was doing zram testing, I found sometimes decompression failed
> since the compression buffer was corrupted. With investigation,
> I found below commit calls cond_resched unconditionally so it could
> make a problem in atomic context if the task is reschedule.

I don't think you're supposed to call unmap_kernel_range() from
atomic context.  At least vfree() punts to __vfree_deferred() if
in_interrupt() is true.  I forget the original reason for why that is.