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From: Hao Ge To: Suren Baghdasaryan Cc: Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Abhishek Bapat , stable@vger.kernel.org References: <20260804122038.190270-1-hao.ge@linux.dev> Content-Language: en-US In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Rspamd-Queue-Id: 05DD2180008 X-Stat-Signature: wa4wtccqgds3gxoohquzburu1stbnj1r X-Rspam-User: X-Rspamd-Server: rspam04 X-HE-Tag: 1785898284-533970 X-HE-Meta: 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 1tF+nhlg sDhs47lVYioaeCfxeNYFfHetbQhKw7sC6+gnbgZUbuKvxMpBPQVO3vkJCfy7P0y+nwqiDS4ajLiwhWC4kwheFF8suqDw/3EDCy13TbJxbZzsjPawnc4YxS1J4Tt22E+M3CjaDPErarj9MIhHV04D4bt/qIQUC5UmBzh0EOTXDgF6SpJ9IS6HMQIge8m+134cw7CGwdu8JZinM6X7pez8euazA7JcILwqRx1Ao9V+d9I5MEitbrTSuDrGH7U1h0cnG+zC3BwCG7XfOgsytLWzFmD7Q1aFvkGf6PypZ6rXVZZcWIWud1ONxgFR7xqXN8RZUXjbkNPIRRvE4W6Ibq9O/bh3zmdQqTcUS4a5psvt6nieeBb/uegCTluyU4xQ01pvAbwCZ Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 2026/8/5 10:26, Hao Ge wrote: > Hi Suren > > > Thanks a lot for your review. > > > On 2026/8/5 04:08, Suren Baghdasaryan wrote: >> On Tue, Aug 4, 2026 at 5:21 AM Hao Ge wrote: >>> In reserve_module_tags(), the tag overflow check is gated on >>> mem_alloc_profiling_enabled(): >>> >>>      if (mem_alloc_profiling_enabled() && !tags_addressable()) >>> >>> If profiling is toggled off at runtime and a module is loaded whose >>> tags exceed the compressed-mode limit, shutdown_mem_profiling() is >>> skipped. vm_module_tags_populate() still maps memory for the tags and >>> the module loads successfully, but the total tag count now exceeds what >>> NR_UNUSED_PAGEFLAG_BITS can address. >>> >>> Once profiling is re-enabled, ref_to_idx() computes each tag's index >>> as its position in the alloc_tag array. update_page_tag_ref() masks >>> it to alloc_tag_ref_mask before storing in page->flags. Indices >>> beyond the mask are truncated and idx_to_ref() resolves them to wrong >>> tags. >>> >>> mem_alloc_profiling_enabled() and mem_profiling_compressed are >>> independent. Once compressed mode is established at boot, it stays >>> active regardless of runtime toggles of mem_profiling. >>> >>> Remove the mem_alloc_profiling_enabled() guard. Also return an error >>> after shutdown_mem_profiling() to skip vm_module_tags_populate(), as >>> the mapped pages would never be reused - shutdown_mem_profiling() sets >>> mem_profiling_support to false, so no future module load enters the >>> codetag path. >>> >>> Fixes: 4835f747d3ed ("alloc_tag: support for page allocation tag >>> compression") >>> Cc: stable@vger.kernel.org >>> Signed-off-by: Hao Ge >> Thanks for the fix, Hao! >> >>> --- >>> Changes in v2: >>> - Return error after shutdown_mem_profiling() to skip unnecessary >>>    vm_module_tags_populate() >>>    v1 link: >>> https://lore.kernel.org/all/20260804064408.105033-1-hao.ge@linux.dev/ >>> --- >>>   mm/alloc_tag.c | 3 ++- >>>   1 file changed, 2 insertions(+), 1 deletion(-) >>> >>> diff --git a/mm/alloc_tag.c b/mm/alloc_tag.c >>> index 52aece27b00e..d8c36430f1c0 100644 >>> --- a/mm/alloc_tag.c >>> +++ b/mm/alloc_tag.c >>> @@ -904,10 +904,11 @@ static void *reserve_module_tags(struct module >>> *mod, unsigned long size, >>>                  int grow_res; >>> >>>                  module_tags.size = offset + size; >>> -               if (mem_alloc_profiling_enabled() && >>> !tags_addressable()) { >> Makes sense but how about replacing mem_alloc_profiling_enabled() with >> mem_profiling_support? Otherwise this warning will be issued multiple >> times if we are loading multiple modules. > > > That's a really good point, this duplicate warning issue will indeed > happen. > > When I thought over your point, I realized using mem_profiling_support > creates a small race window. > > > Thread A（insmod A）                      Thread B (insmod B) > > --------- --------- > > needs_section_mem() -> true > >     needs_section_mem() -> true > >     (profiling still supported) > > reserve_module_tags() > >     overflow -> shutdown > >     mem_profiling_support=false > >     return -ENOSPC > >     reserve_module_tags() > >         mem_profiling_support==false > >         -> overflow check skipped > >         -> vm_module_tags_populate() > >             maps unused tag pages Sorry, my mail client messed up the race diagram, resend it. Thread A (insmod A)                   Thread B (insmod B) ---------------------                 --------------------- needs_section_mem() -> true                                       needs_section_mem() -> true                                       (profiling still supported) reserve_module_tags()   overflow -> shutdown_mem_profiling()   mem_profiling_support = false   return -ENOMEM                                       reserve_module_tags()                                         mem_profiling_support == false                                         -> overflow check skipped                                         -> vm_module_tags_populate()                                            maps unused tag pages > > So I'd rather go with pr_warn_once here. > > >>> +               if (!tags_addressable()) { >>>                          shutdown_mem_profiling(true); >>>                          pr_warn("With module %s there are too many >>> tags to fit in %d page flag bits. Memory allocation profiling is >>> disabled!\n", >>>                                  mod->name, NR_UNUSED_PAGEFLAG_BITS); >>> +                       return ERR_PTR(-ENOSPC); >> This ENOSPC error will be propagated all the way up to the init_module >> syscall and it's not among the error codes currently expected (see: >> https://man7.org/linux/man-pages/man2/init_module.2.html). I suggest >> returning ENOMEM instead. > > > Agree, will change > > > Thanks > > Best Regards > > Hao > >>>                  } >>> >>>                  grow_res = vm_module_tags_populate(); >>> -- >>> 2.25.1 >>>