RE: [Virtio-fs] [PATCH] virtiofsd: Fix data corruption with O_APPEND wirte in writeback mode

[address@hidden]

> On Wed, Oct 23, 2019 at 04:07:52PM -0400, Vivek Goyal wrote:
> > On Wed, Oct 23, 2019 at 09:25:23PM +0900, Misono Tomohiro wrote:
> > > When writeback mode is enabled (-o writeback), O_APPEND handling is
> > > done in kernel. Therefore virtiofsd clears O_APPEND flag when open.
> > > Otherwise O_APPEND flag takes precedence over pwrite() and write
> > > data may corrupt.
> > >
> > > Currently clearing O_APPEND flag is done in lo_open(), but we also
> > > need the same operation in lo_create().
> >
> > > So, factor out the flag
> > > update operation in lo_open() to update_open_flags() and call it in
> > > both lo_open() and lo_create().
> > >
> > > This fixes the failure of xfstest generic/069 in writeback mode
> > > (which tests O_APPEND write data integrity).
> > >
> 
> Hi Misono,
> 
> Have you tried running pjdfstests. Looks like with the patch applied I see 
> following tests failing which were passing without
> the patch. Can you please have a look. I ran daemon with options "-o 
> cache=always -o writeback"

Sorry, I didn't run pjdfstests. I will run the test and check the results.

Thanks,
Misono

> 
> /root/git/pjdfstest/tests/chmod/00.t          (Wstat: 0 Tests: 119 Failed: 1)
>   Failed test:  64
> /root/git/pjdfstest/tests/chown/00.t          (Wstat: 0 Tests: 1323 Failed: 1)
>   Failed test:  946
>   TODO passed:   1107, 1112, 1116, 1122, 1127, 1131, 1137
>                 1142, 1146, 1152, 1157, 1161, 1167, 1172
>                 1176, 1182, 1187
> /root/git/pjdfstest/tests/link/00.t           (Wstat: 0 Tests: 202 Failed: 1)
>   Failed test:  134
> /root/git/pjdfstest/tests/utimensat/01.t      (Wstat: 0 Tests: 7 Failed: 1)
>   Failed test:  4
> Files=232, Tests=8789, 375 wallclock secs ( 4.00 usr  2.65 sys + 51.48 cusr 
> 262.19 csys = 320.32 CPU) Thanks Vivek
> 
> >
> > Hi,
> >
> > Consolidating updation of flags both for lo_create() and lo_open()
> > makes sense to me. I will test it tomorrow.
> >
> > Thanks
> > Vivek
> >
> > > Signed-off-by: Misono Tomohiro <address@hidden>
> > > ---
> > >  contrib/virtiofsd/passthrough_ll.c | 56
> > > +++++++++++++++---------------
> > >  1 file changed, 28 insertions(+), 28 deletions(-)
> > >
> > > diff --git a/contrib/virtiofsd/passthrough_ll.c
> > > b/contrib/virtiofsd/passthrough_ll.c
> > > index e8892c3c32..79fb78ecce 100644
> > > --- a/contrib/virtiofsd/passthrough_ll.c
> > > +++ b/contrib/virtiofsd/passthrough_ll.c
> > > @@ -1733,6 +1733,32 @@ static void lo_releasedir(fuse_req_t req, 
> > > fuse_ino_t ino, struct fuse_file_info
> > >   fuse_reply_err(req, 0);
> > >  }
> > >
> > > +static void update_open_flags(int writeback, struct fuse_file_info
> > > +*fi) {
> > > + /* With writeback cache, kernel may send read requests even
> > > +    when userspace opened write-only */
> > > + if (writeback && (fi->flags & O_ACCMODE) == O_WRONLY) {
> > > +         fi->flags &= ~O_ACCMODE;
> > > +         fi->flags |= O_RDWR;
> > > + }
> > > +
> > > + /* With writeback cache, O_APPEND is handled by the kernel.
> > > +    This breaks atomicity (since the file may change in the
> > > +    underlying filesystem, so that the kernel's idea of the
> > > +    end of the file isn't accurate anymore). In this example,
> > > +    we just accept that. A more rigorous filesystem may want
> > > +    to return an error here */
> > > + if (writeback && (fi->flags & O_APPEND))
> > > +         fi->flags &= ~O_APPEND;
> > > +
> > > + /*
> > > +  * O_DIRECT in guest should not necessarily mean bypassing page
> > > +  * cache on host as well. If somebody needs that behavior, it
> > > +  * probably should be a configuration knob in daemon.
> > > +  */
> > > + fi->flags &= ~O_DIRECT;
> > > +}
> > > +
> > >  static void lo_create(fuse_req_t req, fuse_ino_t parent, const char 
> > > *name,
> > >                 mode_t mode, struct fuse_file_info *fi)  { @@ -1760,12
> > > +1786,7 @@ static void lo_create(fuse_req_t req, fuse_ino_t parent, const 
> > > char *name,
> > >   if (err)
> > >           goto out;
> > >
> > > - /*
> > > -  * O_DIRECT in guest should not necessarily mean bypassing page
> > > -  * cache on host as well. If somebody needs that behavior, it
> > > -  * probably should be a configuration knob in daemon.
> > > -  */
> > > - fi->flags &= ~O_DIRECT;
> > > + update_open_flags(lo->writeback, fi);
> > >
> > >   fd = openat(parent_inode->fd, name,
> > >               (fi->flags | O_CREAT) & ~O_NOFOLLOW, mode); @@ -1966,28
> > > +1987,7 @@ static void lo_open(fuse_req_t req, fuse_ino_t ino,
> > > struct fuse_file_info *fi)
> > >
> > >   fuse_log(FUSE_LOG_DEBUG, "lo_open(ino=%" PRIu64 ", flags=%d)\n",
> > > ino, fi->flags);
> > >
> > > - /* With writeback cache, kernel may send read requests even
> > > -    when userspace opened write-only */
> > > - if (lo->writeback && (fi->flags & O_ACCMODE) == O_WRONLY) {
> > > -         fi->flags &= ~O_ACCMODE;
> > > -         fi->flags |= O_RDWR;
> > > - }
> > > -
> > > - /* With writeback cache, O_APPEND is handled by the kernel.
> > > -    This breaks atomicity (since the file may change in the
> > > -    underlying filesystem, so that the kernel's idea of the
> > > -    end of the file isn't accurate anymore). In this example,
> > > -    we just accept that. A more rigorous filesystem may want
> > > -    to return an error here */
> > > - if (lo->writeback && (fi->flags & O_APPEND))
> > > -         fi->flags &= ~O_APPEND;
> > > -
> > > - /*
> > > -  * O_DIRECT in guest should not necessarily mean bypassing page
> > > -  * cache on host as well. If somebody needs that behavior, it
> > > -  * probably should be a configuration knob in daemon.
> > > -  */
> > > - fi->flags &= ~O_DIRECT;
> > > + update_open_flags(lo->writeback, fi);
> > >
> > >   sprintf(buf, "%i", lo_fd(req, ino));
> > >   fd = openat(lo->proc_self_fd, buf, fi->flags & ~O_NOFOLLOW);
> > > --
> > > 2.21.0
> > >
> > > _______________________________________________
> > > Virtio-fs mailing list
> > > address@hidden
> > > https://www.redhat.com/mailman/listinfo/virtio-fs
> >
> > _______________________________________________
> > Virtio-fs mailing list
> > address@hidden
> > https://www.redhat.com/mailman/listinfo/virtio-fs