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From: Miklos Szeredi <miklos@szeredi.hu>
To: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Colin Walters <walters@verbum.org>,
	syzbot <syzbot+d6ec23007e951dadf3de@syzkaller.appspotmail.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-mm <linux-mm@kvack.org>,
	Miklos Szeredi <mszeredi@redhat.com>,
	syzkaller-bugs <syzkaller-bugs@googlegroups.com>,
	Al Viro <viro@zeniv.linux.org.uk>,
	linux-unionfs@vger.kernel.org
Subject: Re: kernel BUG at mm/hugetlb.c:LINE!
Date: Fri, 22 May 2020 12:05:53 +0200	[thread overview]
Message-ID: <20200522100553.GE13131@miu.piliscsaba.redhat.com> (raw)
In-Reply-To: <78313ae9-8596-9cbe-f648-3152660be9b3@oracle.com>

On Wed, May 20, 2020 at 10:27:15AM -0700, Mike Kravetz wrote:

> I am fairly confident it is all about checking limits and alignment.  The
> filesystem knows if it can/should align to base or huge page size. DAX has
> some interesting additional restrictions, and several 'traditional' filesystems
> check if they are 'on DAX'.


Okay, I haven't looked at DAX vs. overlay.  I'm sure it's going to come up at
some point, if it hasn't already.

> 
> In a previous e-mail, you suggested hugetlb_get_unmapped_area could do the
> length adjustment in hugetlb_get_unmapped_area (generic and arch specific).
> I agree, although there may be the need to add length overflow checks in
> these routines (after round up) as this is done in core code now.  However,
> this can be done as a separate cleanup patch.
> 
> In any case, we need to get the core mmap code to call filesystem specific
> get_unmapped_area if on a union/overlay.  The patch I suggested does this
> by simply calling real_file to determine if there is a filesystem specific
> get_unmapped_area.  The other approach would be to provide an overlayfs
> get_unmapped_area that calls the underlying filesystem get_unmapped_area.

That latter is what's done for all other stacked operations in overlayfs.

Untested patch below.

Thanks,
Miklos

---
 fs/overlayfs/file.c |   12 ++++++++++++
 1 file changed, 12 insertions(+)

--- a/fs/overlayfs/file.c
+++ b/fs/overlayfs/file.c
@@ -757,6 +757,17 @@ static loff_t ovl_remap_file_range(struc
 			    remap_flags, op);
 }
 
+static unsigned long ovl_get_unmapped_area(struct file *file,
+				unsigned long uaddr, unsigned long len,
+				unsigned long pgoff, unsigned long flags)
+{
+	struct file *realfile = file->private_data;
+
+	return (realfile->f_op->get_unmapped_area ?:
+		current->mm->get_unmapped_area)(realfile,
+						uaddr, len, pgoff, flags);
+}
+
 const struct file_operations ovl_file_operations = {
 	.open		= ovl_open,
 	.release	= ovl_release,
@@ -774,6 +785,7 @@ const struct file_operations ovl_file_op
 
 	.copy_file_range	= ovl_copy_file_range,
 	.remap_file_range	= ovl_remap_file_range,
+	.get_unmapped_area	= ovl_get_unmapped_area,
 };
 
 int __init ovl_aio_request_cache_init(void)

  reply	other threads:[~2020-05-22 10:06 UTC|newest]

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-04-06  3:06 syzbot
2020-04-06 22:05 ` Mike Kravetz
2020-05-12 15:04   ` Miklos Szeredi
2020-05-12 18:11     ` Mike Kravetz
2020-05-15 22:15       ` Mike Kravetz
2020-05-18 11:12         ` Miklos Szeredi
2020-05-18 23:22           ` Mike Kravetz
2020-05-18 23:41     ` Colin Walters
2020-05-19  0:35       ` Mike Kravetz
2020-05-20 11:20         ` Miklos Szeredi
2020-05-20 17:27           ` Mike Kravetz
2020-05-22 10:05             ` Miklos Szeredi [this message]
2020-05-28  0:01               ` Mike Kravetz
2020-05-28  8:37                 ` [PATCH v2] ovl: provide real_file() and overlayfs get_unmapped_area() kbuild test robot
2020-05-28 21:01                   ` Mike Kravetz
2020-06-04  9:16                     ` Miklos Szeredi
2020-06-11  0:13                       ` Mike Kravetz
2020-06-11  0:37                         ` Al Viro
2020-06-11  1:36                           ` Matthew Wilcox
2020-06-11  2:17                             ` Al Viro
2020-06-11  2:31                               ` Mike Kravetz

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