On Thu, Mar 10, 2022 at 11:47 AM David Howells <dhowells@xxxxxxxxxx> wrote:
>
> In afs_writepages_region(), if the dirty page we find is undergoing
> writeback or write to cache, but the sync_mode is WB_SYNC_NONE, we go round
> the loop trying the same page again and again with no pausing or waiting
> unless and until another thread manages to clear the writeback and fscache
> flags.
>
> Fix this with three measures:
>
> (1) Advance the start to after the page we found.
>
> (2) Break out of the loop and return if rescheduling is requested.
>
> (3) Arbitrarily give up after a maximum of 5 skips.
>
> Fixes: 31143d5d515e ("AFS: implement basic file write support")
> Reported-by: Marc Dionne <marc.dionne@xxxxxxxxxxxx>
> Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
> ---
>
> fs/afs/write.c | 9 ++++++++-
> 1 file changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/fs/afs/write.c b/fs/afs/write.c
> index 85c9056ba9fb..bd0201f4939a 100644
> --- a/fs/afs/write.c
> +++ b/fs/afs/write.c
> @@ -701,7 +701,7 @@ static int afs_writepages_region(struct address_space *mapping,
> struct folio *folio;
> struct page *head_page;
> ssize_t ret;
> - int n;
> + int n, skips = 0;
>
> _enter("%llx,%llx,", start, end);
>
> @@ -752,8 +752,15 @@ static int afs_writepages_region(struct address_space *mapping,
> #ifdef CONFIG_AFS_FSCACHE
> folio_wait_fscache(folio);
> #endif
> + } else {
> + start += folio_size(folio);
> }
> folio_put(folio);
> + if (wbc->sync_mode == WB_SYNC_NONE) {
> + if (skips >= 5 || need_resched())
> + break;
> + skips++;
> + }
> continue;
> }
Looks good in testing, the problem would show up in xfstests generic/285.
Tested-by: Marc Dionne <marc.dionne@xxxxxxxxxxxx>
Acked-by: Marc Dionne <marc.dionne@xxxxxxxxxxxx>
Marc
