From: Steve French <smfrench@gmail.com>
To: Shyam Prasad N <nspmangalore@gmail.com>
Cc: Bharath SM <bharathsm.hsk@gmail.com>,
pc@cjr.nz, sfrench@samba.org, tom@talpey.com,
linux-cifs@vger.kernel.org, bharathsm@microsoft.com,
ronnie sahlberg <ronniesahlberg@gmail.com>
Subject: Re: [PATCH] cifs: prevent updating file size from server if we have a read/write lease
Date: Sun, 10 Mar 2024 19:32:18 -0500 [thread overview]
Message-ID: <CAH2r5mtvkekMB61pbVu8fmnOrAoY5MrHS_5cU=MYQCOdpBniBQ@mail.gmail.com> (raw)
In-Reply-To: <CANT5p=od_C0TLHN5yURa+baQzj4H1AscX0jDs+weWMH4mSYp0Q@mail.gmail.com>
On Tue, Mar 5, 2024 at 3:41 AM Shyam Prasad N <nspmangalore@gmail.com> wrote:
>
> On Thu, Feb 29, 2024 at 11:23 PM Bharath SM <bharathsm.hsk@gmail.com> wrote:
> >
> > Attached updated patch.
> >
> > On Thu, Feb 29, 2024 at 11:22 PM Bharath SM <bharathsm.hsk@gmail.com> wrote:
> > >
> > > minor update to resolve conflicts.
> > > And Cc: stable@vger.kernel.org
> > >
> > > On Wed, Feb 28, 2024 at 3:57 PM Bharath SM <bharathsm.hsk@gmail.com> wrote:
> > > >
> > > > Attached updated patch to have this fix only for calls from readdir
> > > > i.e cifs_prime_dcache.
> > > >
> > > > On Mon, Feb 26, 2024 at 10:44 AM Steve French <smfrench@gmail.com> wrote:
> > > > >
> > > > > My only worry is that perhaps we should make it more narrow (ie only
> > > > > when called from readdir ie cifs_prime_dcache() rather than also
> > > > > never updating it on query_info calls)
> > > > >
> > > > > On Sun, Feb 25, 2024 at 10:50 PM Bharath SM <bharathsm.hsk@gmail.com> wrote:
> > > > > >
> > > > > > In cases of large directories, the readdir operation may span multiple
> > > > > > round trips to retrieve contents. This introduces a potential race
> > > > > > condition in case of concurrent write and readdir operations. If the
> > > > > > readdir operation initiates before a write has been processed by the
> > > > > > server, it may update the file size attribute to an older value.
> > > > > > Address this issue by avoiding file size updates from server when a
> > > > > > read/write lease.
> > > > > >
> > > > > > Scenario:
> > > > > > 1) process1: open dir xyz
> > > > > > 2) process1: readdir instance 1 on xyz
> > > > > > 3) process2: create file.txt for write
> > > > > > 4) process2: write x bytes to file.txt
> > > > > > 5) process2: close file.txt
> > > > > > 6) process2: open file.txt for read
> > > > > > 7) process1: readdir 2 - overwrites file.txt inode size to 0
> > > > > > 8) process2: read contents of file.txt - bug, short read with 0 bytes
> > > > > >
> > > > > > Signed-off-by: Bharath SM <bharathsm@microsoft.com>
> > > > > > ---
> > > > > > fs/smb/client/file.c | 3 ++-
> > > > > > 1 file changed, 2 insertions(+), 1 deletion(-)
> > > > > >
> > > > > > diff --git a/fs/smb/client/file.c b/fs/smb/client/file.c
> > > > > > index f2db4a1f81ad..e742d0d0e579 100644
> > > > > > --- a/fs/smb/client/file.c
> > > > > > +++ b/fs/smb/client/file.c
> > > > > > @@ -2952,7 +2952,8 @@ bool is_size_safe_to_change(struct cifsInodeInfo *cifsInode, __u64 end_of_file)
> > > > > > if (!cifsInode)
> > > > > > return true;
> > > > > >
> > > > > > - if (is_inode_writable(cifsInode)) {
> > > > > > + if (is_inode_writable(cifsInode) ||
> > > > > > + ((cifsInode->oplock & CIFS_CACHE_RW_FLG) != 0)) {
> > > > > > /* This inode is open for write at least once */
> > > > > > struct cifs_sb_info *cifs_sb;
> > > > > >
> > > > > > --
> > > > > > 2.34.1
> > > > > >
> > > > >
> > > > >
> > > > > --
> > > > > Thanks,
> > > > >
> > > > > Steve
>
> Changes look mostly good.
>
> >> return true;
> >>
> >>- if (is_inode_writable(cifsInode)) {
> >>+ if (is_inode_writable(cifsInode) ||
> >>+ ((cifsInode->oplock & CIFS_CACHE_RW_FLG) != 0 && from_readdir)) {
> >> /* This inode is open for write at least once */
> >> struct cifs_sb_info *cifs_sb;
>
> Why not use CIFS_CACHE_READ(cifsInode) || CIFS_CACHE_WRITE(cifsInode)
> instead of just checking the flag?
> That will cover other cache modes where attrs cannot change outside the client.
I think Bharath's version is safer since if you did CIFS_CACHE_READ
check you would be adding a case where you mounted read-only (and in
that case it looks confusing to allow write size to be updated
locally). It may also be a little risky to allow this when no you
were not able to get a lease from the server and are mounting in
"singleclient" mode.
--
Thanks,
Steve
prev parent reply other threads:[~2024-03-11 0:32 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-02-26 4:50 [PATCH] cifs: prevent updating file size from server if we have a read/write lease Bharath SM
2024-02-26 5:13 ` Steve French
2024-02-28 10:27 ` Bharath SM
2024-02-29 17:52 ` Bharath SM
2024-02-29 17:53 ` Bharath SM
2024-03-05 9:40 ` Shyam Prasad N
2024-03-11 0:32 ` Steve French [this message]
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