On Tue, 2024-11-26 at 15:52 +0100, Jan Kara wrote:
> This reverts commit 7c877586da3178974a8a94577b6045a48377ff25.
>
> Anders and Philippe have reported that recent kernels occasionally hang
> when used with NFS in readahead code. The problem has been bisected to
> 7c877586da3 ("readahead: properly shorten readahead when falling back to
> do_page_cache_ra()"). The cause of the problem is that ra->size can be
> shrunk by read_pages() call and subsequently we end up calling
> do_page_cache_ra() with negative (read huge positive) number of pages.
> Let's revert 7c877586da3 for now until we can find a proper way how the
> logic in read_pages() and page_cache_ra_order() can coexist. This can
> lead to reduced readahead throughput due to readahead window confusion
> but that's better than outright hangs.
>
> Reported-by: Anders Blomdell <anders.blomdell@xxxxxxxxx>
> Reported-by: Philippe Troin <phil@xxxxxxxx>
> CC: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Jan Kara <jack@xxxxxxx>
> ---
> mm/readahead.c | 5 ++---
> 1 file changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/mm/readahead.c b/mm/readahead.c
> index 8f1cf599b572..ea650b8b02fb 100644
> --- a/mm/readahead.c
> +++ b/mm/readahead.c
> @@ -458,8 +458,7 @@ void page_cache_ra_order(struct readahead_control *ractl,
> struct file_ra_state *ra, unsigned int new_order)
> {
> struct address_space *mapping = ractl->mapping;
> - pgoff_t start = readahead_index(ractl);
> - pgoff_t index = start;
> + pgoff_t index = readahead_index(ractl);
> unsigned int min_order = mapping_min_folio_order(mapping);
> pgoff_t limit = (i_size_read(mapping->host) - 1) >> PAGE_SHIFT;
> pgoff_t mark = index + ra->size - ra->async_size;
> @@ -522,7 +521,7 @@ void page_cache_ra_order(struct readahead_control *ractl,
> if (!err)
> return;
> fallback:
> - do_page_cache_ra(ractl, ra->size - (index - start), ra->async_size);
> + do_page_cache_ra(ractl, ra->size, ra->async_size);
> }
>
> static unsigned long ractl_max_pages(struct readahead_control *ractl,
You can add a
Tested-by: Philippe Troin <phil@xxxxxxxx>
tag as I did experiment and validate the fix with that revert on top of 6.11.10.
Phil.
