Re: [PATCH v3] Fix race condition in ext2fs when remounting

[Justus Winter]

Hi James :)

Quoting James Clarke (2015-07-23 19:33:42)
> On some systems, ext2fs.static would regularly hang at startup, as a
> race condition meant it would process paging requests while remounting.
> To fix this, libpager has been altered to allow inhibiting and resuming
> its worker threads, and ext2fs uses this to inhibit paging while
> remounting.

I believe this is the correct solution.  It's nicely written, and well
documented.  Good work :)

I'm merely wondering...

> diff --git a/ext2fs/ext2fs.c b/ext2fs/ext2fs.c
> index d0fdfe7..03c9eed 100644
> --- a/ext2fs/ext2fs.c
> +++ b/ext2fs/ext2fs.c
> @@ -207,10 +207,20 @@ main (int argc, char **argv)
>  error_t
>  diskfs_reload_global_state ()
>  {

... whether we shouldn't protect this function with a lock.  I'm not
sure if concurrent remounts are a problem, but they could very well
be.

Justus

> +  error_t err;
> +
>    pokel_flush (&global_pokel);
>    pager_flush (diskfs_disk_pager, 1);
> -  sblock = NULL;
> +
> +  /* libdiskfs is not responsible for inhibiting paging.  */
> +  err = inhibit_ext2_pager ();
> +  if (err)
> +    return err;
> +
>    get_hypermetadata ();
>    map_hypermetadata ();
> +
> +  resume_ext2_pager ();
> +
>    return 0;
>  }