From: Qian Cai <cai@xxxxxx> Subject: mm/page_io: mark various intentional data races struct swap_info_struct si.flags could be accessed concurrently as noticed by KCSAN, BUG: KCSAN: data-race in scan_swap_map_slots / swap_readpage write to 0xffff9c77b80ac400 of 8 bytes by task 91325 on cpu 16: scan_swap_map_slots+0x6fe/0xb50 scan_swap_map_slots at mm/swapfile.c:887 get_swap_pages+0x39d/0x5c0 get_swap_page+0x377/0x524 add_to_swap+0xe4/0x1c0 shrink_page_list+0x1740/0x2820 shrink_inactive_list+0x316/0x8b0 shrink_lruvec+0x8dc/0x1380 shrink_node+0x317/0xd80 do_try_to_free_pages+0x1f7/0xa10 try_to_free_pages+0x26c/0x5e0 __alloc_pages_slowpath+0x458/0x1290 __alloc_pages_nodemask+0x3bb/0x450 alloc_pages_vma+0x8a/0x2c0 do_anonymous_page+0x170/0x700 __handle_mm_fault+0xc9f/0xd00 handle_mm_fault+0xfc/0x2f0 do_page_fault+0x263/0x6f9 page_fault+0x34/0x40 read to 0xffff9c77b80ac400 of 8 bytes by task 5422 on cpu 7: swap_readpage+0x204/0x6a0 swap_readpage at mm/page_io.c:380 read_swap_cache_async+0xa2/0xb0 swapin_readahead+0x6a0/0x890 do_swap_page+0x465/0xeb0 __handle_mm_fault+0xc7a/0xd00 handle_mm_fault+0xfc/0x2f0 do_page_fault+0x263/0x6f9 page_fault+0x34/0x40 Reported by Kernel Concurrency Sanitizer on: CPU: 7 PID: 5422 Comm: gmain Tainted: G W O L 5.5.0-next-20200204+ #6 Hardware name: HPE ProLiant DL385 Gen10/ProLiant DL385 Gen10, BIOS A40 07/10/2019 Other reads, read to 0xffff91ea33eac400 of 8 bytes by task 11276 on cpu 120: __swap_writepage+0x140/0xc20 __swap_writepage at mm/page_io.c:289 read to 0xffff91ea33eac400 of 8 bytes by task 11264 on cpu 16: swap_set_page_dirty+0x44/0x1f4 swap_set_page_dirty at mm/page_io.c:442 The write is under &si->lock, but the reads are done as lockless. Since the reads only check for a specific bit in the flag, it is harmless even if load tearing happens. Thus, just mark them as intentional data races using the data_race() macro. [cai@xxxxxx: add a missing annotation] Link: http://lkml.kernel.org/r/1581612585-5812-1-git-send-email-cai@xxxxxx Link: http://lkml.kernel.org/r/20200207003601.1526-1-cai@xxxxxx Signed-off-by: Qian Cai <cai@xxxxxx> Cc: Marco Elver <elver@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/page_io.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) --- a/mm/page_io.c~mm-page_io-mark-various-intentional-data-races +++ a/mm/page_io.c @@ -85,7 +85,7 @@ static void swap_slot_free_notify(struct return; sis = page_swap_info(page); - if (!(sis->flags & SWP_BLKDEV)) + if (data_race(!(sis->flags & SWP_BLKDEV))) return; /* @@ -302,7 +302,7 @@ int __swap_writepage(struct page *page, struct swap_info_struct *sis = page_swap_info(page); VM_BUG_ON_PAGE(!PageSwapCache(page), page); - if (sis->flags & SWP_FS) { + if (data_race(sis->flags & SWP_FS)) { struct kiocb kiocb; struct file *swap_file = sis->swap_file; struct address_space *mapping = swap_file->f_mapping; @@ -393,7 +393,7 @@ int swap_readpage(struct page *page, boo goto out; } - if (sis->flags & SWP_FS) { + if (data_race(sis->flags & SWP_FS)) { struct file *swap_file = sis->swap_file; struct address_space *mapping = swap_file->f_mapping; @@ -455,7 +455,7 @@ int swap_set_page_dirty(struct page *pag { struct swap_info_struct *sis = page_swap_info(page); - if (sis->flags & SWP_FS) { + if (data_race(sis->flags & SWP_FS)) { struct address_space *mapping = sis->swap_file->f_mapping; VM_BUG_ON_PAGE(!PageSwapCache(page), page); _
