mainline inclusion from mainline-v6.7-rc8 commit e2c27b803bb664748e090d99042ac128b3f88d92 category: bugfix bugzilla: https://gitee.com/src-openeuler/kernel/issues/I8RRAT Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i... -------------------------------- The following concurrency may cause the data read to be inconsistent with the data on disk: cpu1 cpu2 ------------------------------|------------------------------ // Buffered write 2048 from 0 ext4_buffered_write_iter generic_perform_write copy_page_from_iter_atomic ext4_da_write_end ext4_da_do_write_end block_write_end __block_commit_write folio_mark_uptodate // Buffered read 4096 from 0 smp_wmb() ext4_file_read_iter set_bit(PG_uptodate, folio_flags) generic_file_read_iter i_size_write // 2048 filemap_read unlock_page(page) filemap_get_pages filemap_get_read_batch folio_test_uptodate(folio) ret = test_bit(PG_uptodate, folio_flags) if (ret) smp_rmb(); // Ensure that the data in page 0-2048 is up-to-date. // New buffered write 2048 from 2048 ext4_buffered_write_iter generic_perform_write copy_page_from_iter_atomic ext4_da_write_end ext4_da_do_write_end block_write_end __block_commit_write folio_mark_uptodate smp_wmb() set_bit(PG_uptodate, folio_flags) i_size_write // 4096 unlock_page(page) isize = i_size_read(inode) // 4096 // Read the latest isize 4096, but without smp_rmb(), there may be // Load-Load disorder resulting in the data in the 2048-4096 range // in the page is not up-to-date. copy_page_to_iter // copyout 4096 In the concurrency above, we read the updated i_size, but there is no read barrier to ensure that the data in the page is the same as the i_size at this point, so we may copy the unsynchronized page out. Hence adding the missing read memory barrier to fix this. This is a Load-Load reordering issue, which only occurs on some weak mem-ordering architectures (e.g. ARM64, ALPHA), but not on strong mem-ordering architectures (e.g. X86). And theoretically the problem doesn't only happen on ext4, filesystems that call filemap_read() but don't hold inode lock (e.g. btrfs, f2fs, ubifs ...) will have this problem, while filesystems with inode lock (e.g. xfs, nfs) won't have this problem. Link: https://lkml.kernel.org/r/20231213062324.739009-1-libaokun1@huawei.com Signed-off-by: Baokun Li <libaokun1@huawei.com> Reviewed-by: Jan Kara <jack@suse.cz> Cc: Andreas Dilger <adilger.kernel@dilger.ca> Cc: Christoph Hellwig <hch@infradead.org> Cc: Dave Chinner <david@fromorbit.com> Cc: Matthew Wilcox (Oracle) <willy@infradead.org> Cc: Ritesh Harjani (IBM) <ritesh.list@gmail.com> Cc: Theodore Ts'o <tytso@mit.edu> Cc: yangerkun <yangerkun@huawei.com> Cc: Yu Kuai <yukuai3@huawei.com> Cc: Zhang Yi <yi.zhang@huawei.com> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Conflicts: mm/filemap.c Signed-off-by: Baokun Li <libaokun1@huawei.com> --- mm/filemap.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/mm/filemap.c b/mm/filemap.c index 04e4aad7ed67..c40eb1707cfb 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -2616,6 +2616,15 @@ ssize_t generic_file_buffered_read(struct kiocb *iocb, end_offset = min_t(loff_t, isize, iocb->ki_pos + iter->count); + /* + * Pairs with a barrier in + * block_write_end()->mark_buffer_dirty() or other page + * dirtying routines like iomap_write_end() to ensure + * changes to page contents are visible before we see + * increased inode size. + */ + smp_rmb(); + while ((iocb->ki_pos >> PAGE_SHIFT) + pg_nr > (end_offset + PAGE_SIZE - 1) >> PAGE_SHIFT) put_page(pages[--pg_nr]); -- 2.31.1