From 939325bbad27dc99b8f8cea2791192e5f81b76de Mon Sep 17 00:00:00 2001 From: "Matthew Wilcox (Oracle)" Date: Tue, 19 Jul 2022 16:51:12 +0800 Subject: [PATCH] filemap: Correct the conditions for marking a folio as accessed mainline inclusion from mainline-5.19-rc4 commit 5ccc944dce3df5fd2fd683a7df4fd49d1068eba2 category: bugfix bugzilla: 186896, https://gitee.com/src-openeuler/kernel/issues/I5GZC8 CVE: NA Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5ccc944dce3df5fd2fd683a7df4fd49d1068eba2 ------------------------------------------------- We had an off-by-one error which meant that we never marked the first page in a read as accessed. This was visible as a slowdown when re-reading a file as pages were being evicted from cache too soon. In reviewing this code, we noticed a second bug where a multi-page folio would be marked as accessed multiple times when doing reads that were less than the size of the folio. Abstract the comparison of whether two file positions are in the same folio into a new function, fixing both of these bugs. Reported-by: Yu Kuai Reviewed-by: Kent Overstreet Signed-off-by: Matthew Wilcox (Oracle) Conflict: folios is not supported yet Signed-off-by: Yu Kuai Reviewed-by: Kefeng Wang Signed-off-by: Zheng Zengkai --- mm/filemap.c | 12 +++++++++--- 1 file changed, 9 insertions(+), 3 deletions(-) diff --git a/mm/filemap.c b/mm/filemap.c index 9e209e8a3b0d..edb94663c5df 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -2437,6 +2437,13 @@ static int generic_file_buffered_read_get_pages(struct kiocb *iocb, goto find_page; } +static inline bool pos_same_page(loff_t pos1, loff_t pos2, struct page *page) +{ + unsigned int shift = page_shift(page); + + return (pos1 >> shift == pos2 >> shift); +} + /** * generic_file_buffered_read - generic file read routine * @iocb: the iocb to read @@ -2527,11 +2534,10 @@ ssize_t generic_file_buffered_read(struct kiocb *iocb, writably_mapped = mapping_writably_mapped(mapping); /* - * When a sequential read accesses a page several times, only + * When a read accesses a page several times, only * mark it as accessed the first time. */ - if (iocb->ki_pos >> PAGE_SHIFT != - ra->prev_pos >> PAGE_SHIFT) + if (pos_same_page(iocb->ki_pos, ra->prev_pos -1, pages[0])) mark_page_accessed(pages[0]); for (i = 1; i < pg_nr; i++) mark_page_accessed(pages[i]); -- GitLab