Re: [PATCH] Don't block writes to swap-files with ETXTBSY.

[Wang Yugui <wangyugui@e16-tech.com>]

Hi,

# drop  torvalds@linux-foundation.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org

A Question about ETXTBSY of nfs.
# I tried google/bing, but yet no good info is found.

test case:
/ssd is a  nfs directory
kernel: 5.10.61, 5.4.106 and more

1, on Node1:
[root@T630 ~]# echo -e '#!/bin/bash\necho hello' >/ssd/a.sh
[root@T630 ~]# chmod a+x /ssd/a.sh

2, on Node2:
[root@T640 ~]# /ssd/a.sh
-bash: /ssd/a.sh: /bin/bash: bad interpreter: Text file busy
[root@T640 ~]# bash /ssd/a.sh
hello
[root@T640 ~]# /ssd/a.sh
-bash: /ssd/a.sh: /bin/bash: bad interpreter: Text file busy

Is there any way(flush, sync)  to avoid this ETXTBSY error(Text file busy)?

Best Regards
Wang Yugui (wangyugui@e16-tech.com)
2021/09/02

> On Thu, Aug 26, 2021 at 09:57:39AM +1000, NeilBrown wrote:
> > 
> > Commit dc617f29dbe5 ("vfs: don't allow writes to swap files")
> > broke swap-over-NFS as it introduced an ETXTBSY error when NFS tries to
> > swap-out using ->direct_IO().
> > 
> > There is no sound justification for this error.  File permissions are
> > sufficient to stop non-root users from writing to a swap file, and root
> > must always be cautious not to do anything dangerous.
> > 
> > These checks effectively provide a mandatory write lock on swap, and
> > mandatory locks are not supported in Linux.
> > 
> > So remove all the checks that return ETXTBSY when attempts are made to
> > write to swap.
> 
> Swap files are not just any files and do need a mandatory write lock
> as they are part of the kernel VM and writing to them will mess up
> the kernel badly.  David Howells actually has sent various patches
> to fix swap over NFS in the last weeks.