linux-kernel - Re: [PATCH v3] xen/gntdev: Ignore failure to unmap INVALID_GRANT

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Message-ID: <bba1f8da-37c0-2d23-f529-8b2d866e69cf@suse.com>
Date:   Mon, 11 Jul 2022 08:56:25 +0200
From:   Juergen Gross <jgross@...e.com>
To:     Demi Marie Obenour <demi@...isiblethingslab.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>
Cc:     xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org
Subject: Re: [PATCH v3] xen/gntdev: Ignore failure to unmap
 INVALID_GRANT_HANDLE

On 11.07.22 01:05, Demi Marie Obenour wrote:
> The error paths of gntdev_mmap() can call unmap_grant_pages() even
> though not all of the pages have been successfully mapped.  This will
> trigger the WARN_ON()s in __unmap_grant_pages_done().  The number of
> warnings can be very large; I have observed thousands of lines of
> warnings in the systemd journal.
> 
> Avoid this problem by only warning on unmapping failure if the handle
> being unmapped is not INVALID_GRANT_HANDLE.  The handle field of any
> page that was not successfully mapped will be INVALID_GRANT_HANDLE, so
> this catches all cases where unmapping can legitimately fail.
> 
> Suggested-by: Juergen Gross <jgross@...e.com>
> Cc: stable@...r.kernel.org
> Signed-off-by: Demi Marie Obenour <demi@...isiblethingslab.com>
> Fixes: dbe97cff7dd9 ("xen/gntdev: Avoid blocking in unmap_grant_pages()")

Reviewed-by: Juergen Gross <jgross@...e.com>


Juergen

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