On 29.04.20 18:07, Dave Hansen wrote: > On 4/28/20 3:50 PM, Claudio Imbrenda wrote: >> If a page is inaccesible and it is used for things like sendfile, then >> the content of the page is not always touched, and can be passed >> directly to a driver, causing issues. >> >> This patch fixes the issue by adding a call to arch_make_page_accessible >> in page_cache_pipe_buf_confirm; this fixes the issue. > > I spent about 5 minutes putting together a patch: > > https://sr71.net/~dave/intel/accessible.patch > > It adds a page flag ("daccess") which starts out set. It clears the > flag it when the page is added to the page cache or mapped as anonymous. And that of course does not work. Pages are not made unaccessible at a random point in time. We do check for several page flags and page count before doing so and we also do this while with paqe_ref_freeze to avoid several races. I guess you just hit one of those.
