* Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> [240626 16:59]: > On Tue, 25 Jun 2024 15:11:30 -0400 "Liam R. Howlett" <Liam.Howlett@xxxxxxxxxx> wrote: > > > It is now possible to walk the vma tree using the rcu read locks and is > > beneficial to do so to reduce lock contention. Doing so while a > > MAP_FIXED mapping is executing means that a reader may see a gap in the > > vma tree that should never logically exist - and does not when using the > > mmap lock in read mode. The temporal gap exists because mmap_region() > > calls munmap() prior to installing the new mapping. > > What are the consequences when this race hits? IOW, why do we need to > change anything? > If I understand this correctly the plan is to replace mmap_read_lock(mm) by rcu_read_lock(). So the consequences of a visible gap could be tested by replacing mmap_read_lock(mm) by rcu_read_lock() within the old code. If this is the case I'm willing to test it. Bert Karwatzki
