The patch titled Subject: mm/swap_state: fix a data race in swapin_nr_pages has been added to the -mm tree. Its filename is mm-swap_state-fix-a-data-race-in-swapin_nr_pages.patch This patch should soon appear at http://ozlabs.org/~akpm/mmots/broken-out/mm-swap_state-fix-a-data-race-in-swapin_nr_pages.patch and later at http://ozlabs.org/~akpm/mmotm/broken-out/mm-swap_state-fix-a-data-race-in-swapin_nr_pages.patch Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next and is updated there every 3-4 working days ------------------------------------------------------ From: Qian Cai <cai@xxxxxx> Subject: mm/swap_state: fix a data race in swapin_nr_pages "prev_offset" is a static variable in swapin_nr_pages() that can be accessed concurrently with only mmap_sem held in read mode as noticed by KCSAN, BUG: KCSAN: data-race in swap_cluster_readahead / swap_cluster_readahead write to 0xffffffff92763830 of 8 bytes by task 14795 on cpu 17: swap_cluster_readahead+0x2a6/0x5e0 swapin_readahead+0x92/0x8dc do_swap_page+0x49b/0xf20 __handle_mm_fault+0xcfb/0xd70 handle_mm_fault+0xfc/0x2f0 do_page_fault+0x263/0x715 page_fault+0x34/0x40 1 lock held by (dnf)/14795: #0: ffff897bd2e98858 (&mm->mmap_sem#2){++++}-{3:3}, at: do_page_fault+0x143/0x715 do_user_addr_fault at arch/x86/mm/fault.c:1405 (inlined by) do_page_fault at arch/x86/mm/fault.c:1535 irq event stamp: 83493 count_memcg_event_mm+0x1a6/0x270 count_memcg_event_mm+0x119/0x270 __do_softirq+0x365/0x589 irq_exit+0xa2/0xc0 read to 0xffffffff92763830 of 8 bytes by task 1 on cpu 22: swap_cluster_readahead+0xfd/0x5e0 swapin_readahead+0x92/0x8dc do_swap_page+0x49b/0xf20 __handle_mm_fault+0xcfb/0xd70 handle_mm_fault+0xfc/0x2f0 do_page_fault+0x263/0x715 page_fault+0x34/0x40 1 lock held by systemd/1: #0: ffff897c38f14858 (&mm->mmap_sem#2){++++}-{3:3}, at: do_page_fault+0x143/0x715 irq event stamp: 43530289 count_memcg_event_mm+0x1a6/0x270 count_memcg_event_mm+0x119/0x270 __do_softirq+0x365/0x589 irq_exit+0xa2/0xc0 Link: http://lkml.kernel.org/r/20200402213748.2237-1-cai@xxxxxx Signed-off-by: Qian Cai <cai@xxxxxx> Cc: Marco Elver <elver@xxxxxxxxxx> Cc: Hugh Dickins <hughd@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/swap_state.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) --- a/mm/swap_state.c~mm-swap_state-fix-a-data-race-in-swapin_nr_pages +++ a/mm/swap_state.c @@ -509,10 +509,11 @@ static unsigned long swapin_nr_pages(uns return 1; hits = atomic_xchg(&swapin_readahead_hits, 0); - pages = __swapin_nr_pages(prev_offset, offset, hits, max_pages, + pages = __swapin_nr_pages(READ_ONCE(prev_offset), offset, hits, + max_pages, atomic_read(&last_readahead_pages)); if (!hits) - prev_offset = offset; + WRITE_ONCE(prev_offset, offset); atomic_set(&last_readahead_pages, pages); return pages; _ Patches currently in -mm which might be from cai@xxxxxx are mm-swap_state-fix-a-data-race-in-swapin_nr_pages.patch mm-kmemleak-silence-kcsan-splats-in-checksum.patch mm-frontswap-mark-various-intentional-data-races.patch mm-page_io-mark-various-intentional-data-races.patch mm-page_io-mark-various-intentional-data-races-v2.patch mm-swap_state-mark-various-intentional-data-races.patch mm-swapfile-fix-and-annotate-various-data-races.patch mm-swapfile-fix-and-annotate-various-data-races-v2.patch mm-page_counter-fix-various-data-races-at-memsw.patch mm-memcontrol-fix-a-data-race-in-scan-count.patch mm-list_lru-fix-a-data-race-in-list_lru_count_one.patch mm-mempool-fix-a-data-race-in-mempool_free.patch mm-util-annotate-an-data-race-at-vm_committed_as.patch mm-rmap-annotate-a-data-race-at-tlb_flush_batched.patch mm-annotate-a-data-race-in-page_zonenum.patch mm-swap-annotate-data-races-for-lru_rotate_pvecs.patch