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From: Pavel Shilovsky <piastryyy@gmail.com>
To: ronnie sahlberg <ronniesahlberg@gmail.com>
Cc: Steve French <smfrench@gmail.com>,
	Ronnie Sahlberg <lsahlber@redhat.com>,
	linux-cifs <linux-cifs@vger.kernel.org>
Subject: Re: [PATCH] cifs: add support for fallocate mode 0 for non-sparse files
Date: Thu, 16 Jan 2020 16:27:16 -0800
Message-ID: <CAKywueTB28BQDdBPo=RDHxjPydrKcniRJmbHGaJ3jOD0KKTzVA@mail.gmail.com> (raw)
In-Reply-To: <CAN05THRbNrd=ZmSMO4yE8oHD3Xn93zNTMBRXnJBuf7J3C5Cmow@mail.gmail.com>

чт, 16 янв. 2020 г. в 01:05, ronnie sahlberg <ronniesahlberg@gmail.com>:
>
> The bug is basically that if we extend a file by fallocate mode==0
> and immediately afterwards mmap() the file we will only mmap() as much
> as end-of-file was
> prior to the truncate  and then if we try to touch any
> address in this extended region userspace dies with bus error.
>
> The patch added "extend a file with fallocate mode==0 for NON-Sparse
> files" and caused xfstest to fail.
> The fix is to force us to revalidate the file attributes (the size is
> the important one) when we extend the file so
> mmap() will work properly.
> I have fixed this in the patch and will resend tomorrow after some more testing.
>
> Looking for other SMB2_set_eof() callsites I see we already had the
> same bug for the case of extending a SPARSE

I agree that regardless of file being sparse or not, we should somehow
update a size in the VFS after calling SMB2_set_eof().

> file using fallocate mode==0. I fixed that too and will audit all
> other plases where we use SMB2_set_eof()
> to see if they are safe or not before resending.

One of those places where SMB2_set_eof() is called is
cifs_set_file_size() which does call the following after getting a
successful response from the server:

2250 >-------if (rc == 0) {
2251 >------->-------cifsInode->server_eof = attrs->ia_size;
2252 >------->-------cifs_setsize(inode, attrs->ia_size);
2253 >------->-------cifs_truncate_page(inode->i_mapping, inode->i_size);
2254 >-------}

This is called by cifs_setattr_[no]unix() which does the following afterwards:

2569 >-------if ((attrs->ia_valid & ATTR_SIZE) &&
2570 >-------    attrs->ia_size != i_size_read(inode))
2571 >------->-------truncate_setsize(inode, attrs->ia_size);

truncate_setsize() does  similar things as cifs_setsize() besides
setting cinode->time to 0. This code path probably needs to be
refactored. But putting this aside, for the current fallocate fix I
think we should use the same existing mechanism to update a file size
in the VFS without revalidating the inode.

--
Best regards,
Pavel Shilovsky

  reply index

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-15  1:23 [PATCH 0/1] add support for fallocate mode 0 Ronnie Sahlberg
2020-01-15  1:23 ` [PATCH] cifs: add support for fallocate mode 0 for non-sparse files Ronnie Sahlberg
2020-01-15  1:25   ` Steve French
2020-01-15  2:25     ` ronnie sahlberg
2020-01-15 20:14       ` Steve French
2020-01-16  2:03         ` Steve French
2020-01-16  8:42           ` ronnie sahlberg
2020-01-17  0:27             ` Pavel Shilovsky [this message]
2020-01-17  0:56               ` ronnie sahlberg
2020-01-17  0:04 Ronnie Sahlberg
2020-01-17  1:15 Ronnie Sahlberg

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