4.18-stable review patch. If anyone has any objections, please let me know.
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From: Markus Stockhausen stockhausen@collogia.de
commit dc30b96ab6d569060741572cf30517d3179429a8 upstream.
ondemand_readahead() checks bdi->io_pages to cap the maximum pages that need to be processed. This works until the readit section. If we would do an async only readahead (async size = sync size) and target is at beginning of window we expand the pages by another get_next_ra_size() pages. Btrace for large reads shows that kernel always issues a doubled size read at the beginning of processing. Add an additional check for io_pages in the lower part of the func. The fix helps devices that hard limit bio pages and rely on proper handling of max_hw_read_sectors (e.g. older FusionIO cards). For that reason it could qualify for stable.
Fixes: 9491ae4a ("mm: don't cap request size based on read-ahead setting") Cc: stable@vger.kernel.org Signed-off-by: Markus Stockhausen stockhausen@collogia.de Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- mm/readahead.c | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-)
--- a/mm/readahead.c +++ b/mm/readahead.c @@ -385,6 +385,7 @@ ondemand_readahead(struct address_space { struct backing_dev_info *bdi = inode_to_bdi(mapping->host); unsigned long max_pages = ra->ra_pages; + unsigned long add_pages; pgoff_t prev_offset;
/* @@ -474,10 +475,17 @@ readit: * Will this read hit the readahead marker made by itself? * If so, trigger the readahead marker hit now, and merge * the resulted next readahead window into the current one. + * Take care of maximum IO pages as above. */ if (offset == ra->start && ra->size == ra->async_size) { - ra->async_size = get_next_ra_size(ra, max_pages); - ra->size += ra->async_size; + add_pages = get_next_ra_size(ra, max_pages); + if (ra->size + add_pages <= max_pages) { + ra->async_size = add_pages; + ra->size += add_pages; + } else { + ra->size = max_pages; + ra->async_size = max_pages >> 1; + } }
return ra_submit(ra, mapping, filp);