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? -- Kirill A. Shutemov
