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X-Authority-Analysis: v=2.4 cv=eqbfzppX c=1 sm=1 tr=0 ts=6880a9d8 b=1 cx=c_pps a=qoll8+KPOyaMroiJ2sR5sw==:117 a=qoll8+KPOyaMroiJ2sR5sw==:17 a=6eWqkTHjU83fiwn7nKZWdM+Sl24=:19 a=lCpzRmAYbLLaTzLvsPZ7Mbvzbb8=:19 a=wKuvFiaSGQ0qltdbU6+NXLB8nM8=:19 a=Ol13hO9ccFRV9qXi2t6ftBPywas=:19 a=xqWC_Br6kY4A:10 a=IkcTkHD0fZMA:10 a=Wb1JkmetP80A:10 a=GoEa3M9JfhUA:10 a=xH-5eg9lCkU4znwj824A:9 a=3ZKOabzyN94A:10 a=QEXdDO2ut3YA:10 cc=ntf awl=host:12062 X-Proofpoint-GUID: M6JrRtijGckARKkEvXwBLnk_LVxu_TFj X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUwNzIzMDA3NyBTYWx0ZWRfX7Yn7QnQwZVMc pa6d+4MRNB2NgkamPxb+An1bHpedoqDlzONoj3WRfup+GTnT9fuPPaVVxM3sElh2ogxp757/Rbt AwZ2dKTcUjU/3zxggt/ub16BBtxs1ZXdQOXs9wTq/LPBKiqgfdphIpzNigcaHIMGdyjtMofay5d /f3g/R8IfpzrFpyS/SDXZQEMsrAxYn7qQ1Pz5TBI3cQCpBz4/EAFXcfgxQen282NC2eg6AR3++/ Pe57wc/Bj/ybZJK54LwbBbGxZX2YyT1pEwEtqUWqI1IXYWJ+G9WgMWL2PzxI+Hn+V1o62JC73p8 4Og5NceJfWmImEJ78doxLpc8kFt3AU4dqNuigVKmixlf9c0dcM0OfBU3Ex4MycRT0aNwkSNP+2i DhOEOEn7Itg5eFVUV+eO1+UP2UnVxjTZM/1I+pLnoCYPPorgXgoTdChTwkCGqR43mDuz/D6u X-Proofpoint-ORIG-GUID: M6JrRtijGckARKkEvXwBLnk_LVxu_TFj On Wed, Jul 23, 2025 at 05:14:19PM +0800, Xuanye Liu wrote: > > 在 2025/7/23 17:10, Xuanye Liu 写道: > > 在 2025/7/23 16:42, David Hildenbrand 写道: > >> On 23.07.25 10:05, David Hildenbrand wrote: > >>> On 23.07.25 09:45, Xuanye Liu wrote: > >>>> 在 2025/7/23 15:31, Kees Cook 写道: > >>>>> On Wed, Jul 23, 2025 at 03:23:49PM +0800, Xuanye Liu wrote: > >>>>>> The check_mm() function verifies the correctness of rss counters in > >>>>>> struct mm_struct. Currently, it only prints an alert when a bad > >>>>>> rss-counter state is detected, but lacks sufficient context for > >>>>>> debugging. > >>>>>> > >>>>>> This patch adds a dump_stack() call to provide a stack trace when > >>>>>> the rss-counter state is invalid. This helps developers identify > >>>>>> where the corrupted mm_struct is being checked and trace the > >>>>>> underlying cause of the inconsistency. > >>>>> Why not just convert the pr_alert to a WARN? > >>>> Good idea! I'll gather more feedback from others and then update to v2. > >>> Makes sense to me. > >> After discussion this with Lorenzo off-list, isn't the stack completely misleading/useless in that case? > >> > >> Whatever caused the RSS counter mismatch (e.g., unmapped the wrong pages, missed to unmap pages) quite possibly happened in different context, way way earlier. > >> > >> Why would you think the stack trace would be of any value when destroying an MM (__mmdrop)? > >> > >> Having that said, I really hate these "pr_*("BUG: ...") with passion. Probably we'd want to invoke the panic_on_warn machinery, because something unexpected happened. > >> > > The stack trace dumped here may indeed not reflect the root cause —— > > the actual error could have occurred much earlier, for example during a > > failed or missing page map/unmap operation. > > The current stack (e.g., in __mmdrop() or exit_mmap()) is merely part > > of the cleanup phase. > > Dumping the stack still has some chance of helping identify the issue — at the very least, it > shows which task triggered the check. The stack will be actively misleading because it's highly likely to be totally unrelated. if you want to know the task, just output current->comm :) I think it's not only of no value, it's _ACTIVELY_ misleading. So it's definitely a no to a dump_stack(). I am also not in favour of a WARN_ON() for the same reason. Really we should be catching these elsewhere. If you want to send the patch just outputting thet ask then all good. > > > > > Given that, how should we go about identifying the root cause when such an issue occurs? > > > > Is there any existing way to trace it more effectively, or could we introduce a new mechanism > > to monitor and detect these inconsistencies earlier? > > > > Let’s brainstorm possible solutions together. > > > -- > Thanks, > Xuanye >