On Thu, Sep 17, 2026 at 7:36 PM Hao Ge <[email protected]> wrote: > > Hi Suren > > On 2026/9/18 08:53, Suren Baghdasaryan wrote: > > On Mon, Sep 14, 2026 at 11:59 PM Hao Ge <[email protected]> wrote: > >> > >> After shutdown_mem_profiling() clears mem_profiling_support, > >> needs_section_mem() returns false, so later modules have their codetag > >> section placed as regular data and never enter the alloc_tag maple tree. > >> codetag_load_module() still called load_module(), which allocated a percpu > >> counter for every tag; release_module_tags() could not find these modules > >> on unload, so the counters leaked. > >> > >> Return -EOPNOTSUPP from load_module() when profiling is off: > >> codetag_module_init() drops the module's cmod, no counters are allocated > >> and the module loads without its tags. codetag_unload_module() now always > >> calls free_section_mem(), since a module whose module_load() returned > >> -EOPNOTSUPP is not in the idr but may still hold a reserved section. > >> > >> Reported-by: Sashiko <[email protected]> > >> Fixes: 4835f747d3ed ("alloc_tag: support for page allocation tag > >> compression") > >> Cc: [email protected] > >> Suggested-by: Suren Baghdasaryan <[email protected]> > >> Acked-by: Suren Baghdasaryan <[email protected]> > > > > Yeah, I guess I didn't think about alternatives... > > > > When mem_profiling_support=false, why can't load_module() skip > > allocating percpu counters, zero out the whole area between start_tag > > and stop_tag and return 0 as success (mem_profiling_support is not > > enabled, so we acted accordingly)? > > Module will be added into maple tree and later codetag_unload_module() > > will find the module, call release_module_tags() (which is a NOOP > > because tag->counter==NULL) and finally call free_section_mem(). This > > seems more natural than special-casing with EOPNOTSUPP. WDYT? > > > > I see, but the module would then sit in the idr with NULL-counter > tags that become visible to readers which today never expect that state. > > alloc_tag_top_users calls codetag_next_ct() to find the next codetag > and alloc_tag_read() would do per_cpu_ptr(NULL) for each cpu - plain > pointer arithmetic onto a wild address, an oops straight out of the > OOM report. > > https://elixir.bootlin.com/linux/v7.3-rc3/source/mm/alloc_tag.c#L503 > > So if the codetag section within this codetag_type ends up meaningless, > is there a reason we still return success? We will still maintain > cttype->count > and allocate a slot for this module inside mod_idr. > > I'd rather keep the -EOPNOTSUPP version (your original suggestion), > also because the comments in load_module() and codetag_module_init() > already document this scenario. > > WDYT?
Ok, fair enough. I think your current fix is the simplest way to resolve this issue, so let's keep it simple. Acked-by: Suren Baghdasaryan <[email protected]> > > Thanks > Best Regards > Hao > > >> Signed-off-by: Hao Ge <[email protected]> > >> --- > >> lib/codetag.c | 10 ++++++++-- > >> mm/alloc_tag.c | 4 ++++ > >> 2 files changed, 12 insertions(+), 2 deletions(-) > >> > >> diff --git a/lib/codetag.c b/lib/codetag.c > >> index a9cda4c962a3..a0b600720afc 100644 > >> --- a/lib/codetag.c > >> +++ b/lib/codetag.c > >> @@ -240,7 +240,9 @@ static int codetag_module_init(struct codetag_type > >> *cttype, struct module *mod) > >> > >> if (err < 0) { > >> kfree(cmod); > >> - return err; > >> + /* -EOPNOTSUPP means we can load the module without its > >> tag. */ > >> + if (err != -EOPNOTSUPP) > >> + return err; > >> } > >> > >> return 0; > >> @@ -388,7 +390,11 @@ void codetag_unload_module(struct module *mod) > >> ++cttype->content_id; > >> } > >> up_write(&cttype->mod_lock); > >> - if (found && cttype->desc.free_section_mem) > >> + /* > >> + * A module whose module_load() returned -EOPNOTSUPP is not > >> + * in the idr but may still hold reserved section memory. > >> + */ > >> + if (cttype->desc.free_section_mem) > >> cttype->desc.free_section_mem(mod, true); > >> } > >> mutex_unlock(&codetag_lock); > >> diff --git a/mm/alloc_tag.c b/mm/alloc_tag.c > >> index 5836803898ad..1ca0409b492b 100644 > >> --- a/mm/alloc_tag.c > >> +++ b/mm/alloc_tag.c > >> @@ -988,6 +988,10 @@ static int load_module(struct module *mod, struct > >> codetag *start, struct codetag > >> struct alloc_tag *stop_tag; > >> struct alloc_tag *tag; > >> > >> + /* Profiling disabled: load the module without its tags. */ > >> + if (!mem_profiling_support) > >> + return -EOPNOTSUPP; > >> + > >> /* percpu counters for core allocations are already statically > >> allocated */ > >> if (!mod) > >> return 0; > >> -- > >> 2.25.1 > >>
