6.12-stable review patch. If anyone has any objections, please let me know.
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From: Jan Kara jack@suse.cz
commit a220d6b95b1ae12c7626283d7609f0a1438e6437 upstream.
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.
Link: https://lkml.kernel.org/r/20241126145208.985-1-jack@suse.cz Fixes: 7c877586da31 ("readahead: properly shorten readahead when falling back to do_page_cache_ra()") Reported-by: Anders Blomdell anders.blomdell@gmail.com Reported-by: Philippe Troin phil@fifi.org Signed-off-by: Jan Kara jack@suse.cz Tested-by: Philippe Troin phil@fifi.org Cc: Matthew Wilcox willy@infradead.org Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- mm/readahead.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-)
--- a/mm/readahead.c +++ b/mm/readahead.c @@ -453,8 +453,7 @@ void page_cache_ra_order(struct readahea 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; @@ -517,7 +516,7 @@ void page_cache_ra_order(struct readahea 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,