On Tue, Sep 15, 2026 at 11:00 PM Hao Ge <[email protected]> wrote: > > Hi Suren > > Thanks for you review. > > On 2026/9/16 05:09, Suren Baghdasaryan wrote: > > On Mon, Sep 14, 2026 at 11:59 PM Hao Ge <[email protected]> wrote: > >> > >> The reservation is already stored in the maple tree when > >> vm_module_tags_populate() fails. A failed load never unloads the > >> module, so nothing releases the entry. Release it and roll > >> module_tags.size back. Without the rollback a concurrent load that > >> already passed needs_section_mem() can reuse the freed gap, skip > >> vm_module_tags_populate() and write to unmapped memory. > >> > >> vmap_pages_range() may have installed some PTEs before failing. A > >> retry to populate the same range would BUG on them, so undo them, > >> but only if vmap actually ran. > >> > >> Fixes: 4835f747d3ed ("alloc_tag: support for page allocation tag > >> compression") > >> Fixes: 0f9b685626da ("alloc_tag: populate memory for module tags as > >> needed") > > > > If a patch fixes two other patches, it likely needs to be split so > > that each part fixes one patch only. But read on please. I'm not sure > > if one of the fixes is correct. > > > > Kept them in one patch because they only make sense together. > > After a failed populate the reservation is released and the > size rolled back, so the next load takes the same gap and calls > vm_module_tags_populate() again, and that retry would trip over > the PTEs the failed vmap left behind. > > Without the rollback a load that already passed needs_section_mem() > just reuses the gap, skips populate and writes to unmapped memory. > So splitting them leaves each half broken.
Yeah, that's why I think vmap_pages_range() cleanup should be a completely separate patch with vmap_pages_range() doing cleanup itself. > > >> Reported-by: Sashiko <[email protected]> > >> Cc: [email protected] > >> Signed-off-by: Hao Ge <[email protected]> > >> --- > >> mm/alloc_tag.c | 10 ++++++++++ > >> 1 file changed, 10 insertions(+) > >> > >> diff --git a/mm/alloc_tag.c b/mm/alloc_tag.c > >> index 2070e682fe10..95ddf5b743d0 100644 > >> --- a/mm/alloc_tag.c > >> +++ b/mm/alloc_tag.c > >> @@ -804,6 +804,13 @@ static int vm_module_tags_populate(void) > >> next_page, PAGE_SHIFT) < 0) { > >> release_pages_arg arg = { .pages = next_page }; > >> > >> + /* > >> + * vmap_pages_range() only runs once all pages were > >> + * allocated, and it may have installed some > >> mappings > >> + * before failing. Undo them. > > > > If vmap_pages_range() failed to map the range, why should we need to > > undo it? If it indeed leaves some partial mapping when failing then I > > would argue that vmap_pages_range() should be undoing these partial > > mappings itself before returning the error. > > > Yeah it does - none of the paths under vmap_pages_range() undo themselves on > error. Hmm. I wonder if this behavior is intentional or requires a fix. The only possible reason I can think of is performance but I can't imagine a failure to map is a performance-critical case. +David Hildenbrand (Red Hat), +Lorenzo Stoakes (Oracle) what do you guys think? Shouldn't vmap_pages_range() undo its possible partial mapping when it fails? > pcpu_map_pages does perform cleanup on its own as well. There may be other > similar sites. > https://elixir.bootlin.com/linux/v7.3-rc3/source/mm/percpu-vm.c#L255 > so I did the same here. > > If we really want vmap_pages_range() to handle this cleanup internally, I > believe that would > be a relatively large change, and we would need to consider many more cases. > So I think we keep > the current behaviour for now. Yeah, I understand it would require a deeper cut but if that's the right way to handle this we might as well do that. Let's see what MM folks think. > > Thanks > Best Regards > Hao > > >> + */ > >> + if (nr == more_pages) > >> + vunmap_range(phys_end, phys_end + (nr << > >> PAGE_SHIFT)); > >> /* Clean up and error out */ > >> release_pages(arg, nr); > >> return -ENOMEM; > >> @@ -947,6 +954,7 @@ static void *reserve_module_tags(struct module *mod, > >> unsigned long size, > >> return ret; > >> > >> if (module_tags.size < offset + size) { > >> + unsigned long prev_size = module_tags.size; > >> int grow_res; > >> > >> module_tags.size = offset + size; > >> @@ -961,6 +969,8 @@ static void *reserve_module_tags(struct module *mod, > >> unsigned long size, > >> shutdown_mem_profiling(true); > >> pr_err("Failed to allocate memory for allocation > >> tags in the module %s. Memory allocation profiling is disabled!\n", > >> mod->name); > >> + release_module_tags(mod, false); > >> + module_tags.size = prev_size; > > > > Yes, this one is a valid fix. It fixes 0f9b685626da commit. > > > >> return ERR_PTR(grow_res); > >> } > >> } > >> -- > >> 2.25.1 > >>
