linux-kernel - Re: [PATCH] Revert "mm/vunmap: add cond_resched() in vunmap_pmd

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Date:   Thu, 5 Nov 2020 17:16:02 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     Minchan Kim <minchan@...nel.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, linux-mm <linux-mm@...ck.org>,
        "Aneesh Kumar K . V" <aneesh.kumar@...ux.ibm.com>,
        Harish Sriram <harish@...ux.ibm.com>, stable@...r.kernel.org
Subject: Re: [PATCH] Revert "mm/vunmap: add cond_resched() in
 vunmap_pmd_range"

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.