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X-MS-Exchange-CrossTenant-AuthSource: CO1PR11MB4820.namprd11.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 08 Mar 2024 01:06:07.9537 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 46c98d88-e344-4ed4-8496-4ed7712e255d X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: 0ZwUvmuPbRGJ78yQ+IAIk+I6r9wOzqmy8fc5OxMl34c/rdg9XK82oQ+6RUMdwEO2uZ01Wwbr19Ix/gqsHj22Gg== X-MS-Exchange-Transport-CrossTenantHeadersStamped: IA0PR11MB7815 X-OriginatorOrg: intel.com X-Rspam-User: X-Stat-Signature: sbf4cakgi4uhqjjzx6nbijd16ftxssd8 X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 8151D1A0022 X-HE-Tag: 1709859975-694350 X-HE-Meta: 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 8b/5IWgK X6hUaqjV9pRrPcnJ55513+fvYhHEgAFNgTSocYBdYphPuvbttb8YMYIsj/V8jgoZqnquniwjzvPPgUNxqgqSIME7A3/lNsGzSu/dA6dd7mdFCQQv1luGCXzLpW3uT33q7LMWTUajBMQUd+cAi3t8dde6OVUE7Kc47wGLTT7Oe3rRSt86RNC5dQtZ84EVad5F5eBbc/nsRI5qq7e4UfhS2DxNap7TJ/uhDRx93Y4iPWXS2i59CYvZvwltdm4Uwoor5BVhw1hqIoIjL0c/8dAbL1TeZMWnaBHmpkUCgxky5Y9cx6d2HoXz9S3dXurp9r2eEosNr X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 3/7/2024 10:05 PM, Matthew Wilcox wrote: > On Thu, Mar 07, 2024 at 09:50:09PM +0800, Yin, Fengwei wrote: >> >> >> On 3/7/2024 4:56 PM, wrote: >>> I just want to make sure I've understood correctly: CPU1's folio_put() >>> is not the last reference, and it keeps iterating through the local >>> list. Then CPU2 does the final folio_put() which causes list_del_init() >>> to modify the local list concurrently with CPU1's iteration, so CPU1 >>> probably goes into the weeds? >> >> My understanding is this can not corrupt the folio->deferred_list as >> this folio was iterated already. > > I am not convinced about that at all. It's possible this isn't the only > problem, but deleting something from a list without holding (the correct) > lock is something you have to think incredibly hard about to get right. > I didn't bother going any deeper into the analysis once I spotted the > locking problem, but the proof is very much on you that this is not a bug! Removing folio from deferred_list in folio_put() also needs require split_queue_lock. So my understanding is no deleting without hold correct lock. local list iteration is impacted. But that's not the issue Ryan hit here. > >> But I did see other strange thing: >> [ 76.269942] page: refcount:0 mapcount:1 mapping:0000000000000000 >> index:0xffffbd0a0 pfn:0x2554a0 >> [ 76.270483] note: kcompactd0[62] exited with preempt_count 1 >> [ 76.271344] head: order:0 entire_mapcount:1 nr_pages_mapped:0 pincount:0 >> >> This large folio has order 0? Maybe folio->_flags_1 was screwed? >> >> In free_unref_folios(), there is code like following: >> if (order > 0 && folio_test_large_rmappable(folio)) >> folio_undo_large_rmappable(folio); >> >> But with destroy_large_folio(): >> if (folio_test_large_rmappable(folio)) >> >> folio_undo_large_rmappable(folio); >> >> Can it connect to the folio has zero refcount still in deferred list >> with Matthew's patch? >> >> >> Looks like folio order was cleared unexpected somewhere. > > No, we intentionally clear it: > > free_unref_folios -> free_unref_page_prepare -> free_pages_prepare -> > page[1].flags &= ~PAGE_FLAGS_SECOND; > > PAGE_FLAGS_SECOND includes the order, which is why we have to save it > away in folio->private so that we know what it is in the second loop. > So it's always been cleared by the time we call free_page_is_bad(). Oh. That's the key. Thanks a lot for detail explanation. I thought there was a bug in other place, covered by destroy_large_folio() but exposed by free_unref_folios()... Regards Yin, Fengwei