"Kirill A. Shutemov" <kirill@xxxxxxxxxxxxx> writes: > On Tue, Feb 11, 2020 at 11:44:06AM -0500, Jeff Moyer wrote: >> Hi, Justin, >> >> Justin He <Justin.He@xxxxxxx> writes: >> >> Thanks for the report. But this commit 83d116c53058 doesn't add the >> >> new clear_page code path. Besides the pte_mkyoung part, It just refines >> >> the codes(no functional change) and add a WARN_ON_ONCE to indicate >> >> there is any obscure case before. >> > >> > I can't reproduce it with your provided test file on my arm64 qemu with >> > a pmem device. >> > Could you do me a favor that just revert 83d116c53058 but keep that >> > WARN_ON_ONCE after clear_page()? Is there any difference? >> > Thanks for your help >> >> Below is the patch I used to put the WARN_ON_ONCE after the clear_page, >> just to be sure that's what you intended. So with 83d116c53058 >> reverted, and the below patch applied, the WARN_ON_ONCE does not >> trigger. > > I cannot explain this. There is no locking to prevent the same scenario > before. It might be an timing difference. > > Could try to put a delay before the copy to make race window larger? I reverted my change to the reproducer, and now it triggers the warning. -Jeff
