On Mon, Dec 19, 2022 at 04:01:00PM +0800, Baoquan He wrote: > On 12/17/22 at 11:44am, Lorenzo Stoakes wrote: > > On Sat, Dec 17, 2022 at 09:54:30AM +0800, Baoquan He wrote: > > > @@ -2229,8 +2236,12 @@ void vm_unmap_ram(const void *mem, unsigned int count) > > > return; > > > } > > > > > > - va = find_vmap_area(addr); > > > + spin_lock(&vmap_area_lock); > > > + va = __find_vmap_area((unsigned long)addr, &vmap_area_root); > > > BUG_ON(!va); > > > + if (va) > > > + va->flags &= ~VMAP_RAM; > > > + spin_unlock(&vmap_area_lock); > > > debug_check_no_locks_freed((void *)va->va_start, > > > (va->va_end - va->va_start)); > > > free_unmap_vmap_area(va); > > > > Would it be better to perform the BUG_ON() after the lock is released? You > > already check if va exists before unmasking so it's safe. > > It's a little unclear to me why we care BUG_ON() is performed before or > after the lock released. We won't have a stable kernel after BUG_ON()(), > right? BUG_ON()'s can be recoverable in user context and it would be a very simple change that would not fundamentally alter anything to simply place the added lines prior to the BUG_ON(). The code as-is doesn't really make sense anyway, you BUG_ON(!va) then check if va is non-null, then immediately the function afterwards passes va around as if it were not null, so I think it'd also be an aesthetic and logical improvement :) > > > > Also, do we want to clear VMAP_BLOCK here? > > I do, but I don't find a good place to clear VMAP_BLOCK. > > In v1, I tried to clear it in free_vmap_area_noflush() as below, > Uladzislau dislikes it. So I remove it. My thinking is when we unmap and > free the vmap area, the vmap_area is moved from vmap_area_root into > &free_vmap_area_root. When we allocate a new vmap_area via > alloc_vmap_area(), we will allocate a new va by kmem_cache_alloc_node(), > the va->flags must be 0. Seems not initializing it to 0 won't impact > thing. > You are at this point clearing the VMAP_RAM flag though, so if it is unimportant what the flags are after this call, why are you clearing this one? It is just a little confusing, I wonder whether the VMAP_BLOCK flag is necessary at all, is it possible to just treat a non-VMAP_BLOCK VMAP_RAM area as if it were simply a fully occupied block? Do we gain much by the distinction? > diff --git a/mm/vmalloc.c b/mm/vmalloc.c > index 5d3fd3e6fe09..d6f376060d83 100644 > --- a/mm/vmalloc.c > +++ b/mm/vmalloc.c > @@ -1815,6 +1815,7 @@ static void free_vmap_area_noflush(struct vmap_area *va) > > spin_lock(&vmap_area_lock); > unlink_va(va, &vmap_area_root); > + va->flags = 0; > spin_unlock(&vmap_area_lock); > > nr_lazy = atomic_long_add_return((va->va_end - va->va_start) >> > > > >
