On Mon, Feb 10, 2020 at 10:01:34PM -0500, Qian Cai wrote: > struct file_ra_state ra.mmap_miss could be accessed concurrently during > page faults as noticed by KCSAN, > > BUG: KCSAN: data-race in filemap_fault / filemap_map_pages > > write to 0xffff9b1700a2c1b4 of 4 bytes by task 3292 on cpu 30: > filemap_fault+0x920/0xfc0 > do_sync_mmap_readahead at mm/filemap.c:2384 > (inlined by) filemap_fault at mm/filemap.c:2486 > __xfs_filemap_fault+0x112/0x3e0 [xfs] > xfs_filemap_fault+0x74/0x90 [xfs] > __do_fault+0x9e/0x220 > do_fault+0x4a0/0x920 > __handle_mm_fault+0xc69/0xd00 > handle_mm_fault+0xfc/0x2f0 > do_page_fault+0x263/0x6f9 > page_fault+0x34/0x40 > > read to 0xffff9b1700a2c1b4 of 4 bytes by task 3313 on cpu 32: > filemap_map_pages+0xc2e/0xd80 > filemap_map_pages at mm/filemap.c:2625 > do_fault+0x3da/0x920 > __handle_mm_fault+0xc69/0xd00 > handle_mm_fault+0xfc/0x2f0 > do_page_fault+0x263/0x6f9 > page_fault+0x34/0x40 > > Reported by Kernel Concurrency Sanitizer on: > CPU: 32 PID: 3313 Comm: systemd-udevd Tainted: G W L 5.5.0-next-20200210+ #1 > Hardware name: HPE ProLiant DL385 Gen10/ProLiant DL385 Gen10, BIOS A40 07/10/2019 > > ra.mmap_miss is used to contribute the readahead decisions, a data race > could be undesirable. Both the read and write is only under > non-exclusive mmap_sem, two concurrent writers could even overflow the > counter. Fixing the underflow by writing to a local variable before > committing a final store to ra.mmap_miss given a small inaccuracy of the > counter should be acceptable. > > Suggested-by: Kirill A. Shutemov <kirill@xxxxxxxxxxxxx> > Signed-off-by: Qian Cai <cai@xxxxxx> That's more than Suggested-by. The correct way to submit this patch is: From: Kirill A. Shutemov <kirill@xxxxxxxxxxxxx> (at the top of the patch, so it gets credited to Kirill) then in this section: Signed-off-by: Kirill A. Shutemov <kirill@xxxxxxxxxxxxx> Tested-by: Qian Cai <cai@xxxxxx> And now you can add: Reviewed-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
