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Message-ID: <20200714034111.GD1696@sol.localdomain>
Date: Mon, 13 Jul 2020 20:41:11 -0700
From: Eric Biggers <ebiggers@...nel.org>
To: Hillf Danton <hdanton@...a.com>
Cc: syzbot <syzbot+7a0d9d0b26efefe61780@...kaller.appspotmail.com>,
akpm@...ux-foundation.org, arve@...roid.com, christian@...uner.io,
devel@...verdev.osuosl.org, gregkh@...uxfoundation.org,
hughd@...gle.com, joel@...lfernandes.org,
linux-kernel@...r.kernel.org, linux-mm@...ck.org, maco@...roid.com,
syzkaller-bugs@...glegroups.com, tkjos@...roid.com,
Markus Elfring <Markus.Elfring@....de>
Subject: Re: possible deadlock in shmem_fallocate (4)
On Tue, Jul 14, 2020 at 11:32:52AM +0800, Hillf Danton wrote:
>
> Add FALLOC_FL_NOBLOCK and on the shmem side try to lock inode upon the
> new flag. And the overall upside is to keep the current gfp either in
> the khugepaged context or not.
>
> --- a/include/uapi/linux/falloc.h
> +++ b/include/uapi/linux/falloc.h
> @@ -77,4 +77,6 @@
> */
> #define FALLOC_FL_UNSHARE_RANGE 0x40
>
> +#define FALLOC_FL_NOBLOCK 0x80
> +
You can't add a new UAPI flag to fix a kernel-internal problem like this.
- Eric
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