On Thu, Aug 12, 2021 at 7:48 AM Eric W. Biederman <ebiederm@xxxxxxxxxxxx> wrote: > > Given that MAP_PRIVATE for shared libraries is our strategy for handling > writes to shared libraries perhaps we just need to use MAP_POPULATE or a > new related flag (perhaps MAP_PRIVATE_NOW) No. That would be horrible for the usual bloated GUI libraries. It might help some (dynamic page faults are not cheap either), but it would hurt a lot. This is definitely a "if you overwrite a system library while it's being used, you get to keep both pieces" situation. The kernel ETXTBUSY thing is purely a courtesy feature, and as people have noticed it only really works for the main executable because of various reasons. It's not something user space should even rely on, it's more of a "ok, you're doing something incredibly stupid, and we'll help you avoid shooting yourself in the foot when we notice". Any distro should make sure their upgrade tools don't just truncate/write to random libraries executables. And if they do, it's really not a kernel issue. This patch series basically takes this very historical error return, and simplifies and clarifies the implementation, and in the process might change some very subtle corner case (unmapping the original executable entirely?). I hope (and think) it wouldn't matter exactly because this is a "courtesy error" rather than anything that a sane setup would _depend_ on, but hey, insane setups clearly exist. Linus