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Fri, 06 Feb 2026 04:17:07 -0800 (PST) MIME-Version: 1.0 References: In-Reply-To: From: Zw Tang Date: Fri, 6 Feb 2026 20:16:55 +0800 X-Gm-Features: AZwV_QjejJSCC1v7jUQprGWkxeFN35WAUicWGf_C1T0bQ5M7jfVAg14PzKRDigk Message-ID: Subject: =?UTF-8?B?5Zue5aSNOiBbQlVHXSByY3UgZGV0ZWN0ZWQgc3RhbGwgaW4gc2htZW1fZmlsZV93cml0ZQ==?= =?UTF-8?B?X2l0ZXI=?= To: Kunwu Chan , "linux-mm@kvack.org" , "rcu@vger.kernel.org" Cc: "hughd@google.com" , "akpm@linux-foundation.org" , "david@kernel.org" , "chrisl@kernel.org" , "kasong@tencent.com" , "paulmck@kernel.org" , "frederic@kernel.org" , "linux-kernel@vger.kernel.org" Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Stat-Signature: xpp7qqkfguhr9eoguu3s9emt9icx4n6w X-Rspamd-Queue-Id: 8C3D0160005 X-Rspam-User: X-Rspamd-Server: rspam04 X-HE-Tag: 1770380228-956018 X-HE-Meta: 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 9XLsOZgI 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 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: Hi David, hi Kunwu, thanks a lot for the suggestions. I reran the reproducer with CONFIG_PROVE_LOCKING=3Dy, CONFIG_LOCKDEP=3Dy, CONFIG_DEBUG_LOCK_ALLOC=3Dy e= nabled. Based on the lockdep-enabled run, here is what I can clarify: Lockdep does not report any lock inversion, recursive locking, or circular dependency. The samples showing __mod_zone_page_state() do not appear to indicate a blocking point; this frame indeed seems to be just where the task was sampled. >From the timeline of the reports, the earliest problematic behavior appears before the MM/LRU-heavy paths. In the first hung-task report, multiple repro1 threads are already blocked = in: down_write() =E2=94=94=E2=94=80 rwbase_write_lock() =E2=94=94=E2=94=80 __rt_mutex_slowlock_locked() =E2=94=94=E2=94=80 rt_mutex_schedule() via the do_vfs_ioctl() =E2=86=92 perf_fasync() path, and are in D state for more than 143 seconds at that point. After several threads are stuck there, the system degrades further: other threads remain in R state, spending long, uninterrupted time in MM allocation / LRU paths (alloc_pages(), get_page_from_freelist(), __handle_mm_fault()), without hitting reschedule points. This then leads to RCU preempt stalls, and eventually workqueue lockups (e.g. vmstat_shepherd, do_cache_clean, wb_workfn). Lockdep=E2=80=99s =E2=80=9Cshow all locks held=E2=80=9D output does not sho= w the blocked repro1 threads holding any MM/LRU/zone locks themselves; they typically only hold the filesystem mutex at that point, which suggests the contended RT rwsem is held elsewhere. Overall, this currently looks less like a single blocking bug in __mod_zone_page_state(), and more like a PREEMPT_RT-specific starvation scenario, where long-held RT rwsems in the ioctl/perf path combined with long CPU-bou= nd MM/LRU execution amplify into RCU starvation and workqueue lockups. Below is the earliest hung-task report from the lockdep-enabled run for reference: [386.499937] INFO: task repro1:2066 blocked for more than 143 seconds. [386.499956] Not tainted 6.19.0-rc7 #4 [386.499964] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. [386.499970] task:repro1 state:D stack:28400 pid:2066 tgid:2066 ppid:293 2 [386.500022] Call Trace: [386.500027] [386.500037] __schedule+0x1198/0x3f00 [386.500069] ? io_schedule_timeout+0x80/0x80 [386.500088] ? kvm_sched_clock_read+0x16/0x20 [386.500111] ? local_clock_noinstr+0xf/0xc0 [386.500125] ? __rt_mutex_slowlock_locked.constprop.0+0xecd/0x30c0 [386.500148] rt_mutex_schedule+0x9f/0xe0 [386.500171] __rt_mutex_slowlock_locked.constprop.0+0xedc/0x30c0 [386.500197] ? down_write_trylock+0x1a0/0x1a0 [386.500222] ? lock_acquired+0xbd/0x340 [386.500245] rwbase_write_lock+0x744/0xa80 [386.500266] ? perf_fasync+0xc0/0x130 [386.500284] ? rt_mutex_adjust_prio_chain.isra.0+0x3240/0x3240 [386.500304] ? kvm_sched_clock_read+0x16/0x20 [386.500329] ? perf_fasync+0xc0/0x130 [386.500344] ? local_clock+0x10/0x20 [386.500364] ? lock_contended+0x189/0x420 [386.500385] down_write+0x6e/0x1e0 [386.500405] perf_fasync+0xc0/0x130 [386.500421] ? perf_cgroup_css_free+0x50/0x50 [386.500440] do_vfs_ioctl+0x9b9/0x1480 [386.500457] ? lock_vma_under_rcu+0x7ee/0xd90 [386.500475] ? ioctl_file_clone+0xf0/0xf0 [386.500490] ? lock_is_held_type+0xa0/0x110 [386.500506] ? handle_mm_fault+0x5a6/0x9d0 [386.500526] ? kvm_sched_clock_read+0x16/0x20 [386.502053] ? local_clock_noinstr+0xf/0xc0 [386.502073] ? handle_mm_fault+0x5a6/0x9d0 [386.502092] ? exc_page_fault+0xb0/0x180 [386.502106] ? kvm_sched_clock_read+0x16/0x20 [386.502129] ? local_clock_noinstr+0xf/0xc0 [386.502142] ? exc_page_fault+0xb0/0x180 [386.502154] ? local_clock+0x10/0x20 [386.502174] ? lock_release+0x258/0x3c0 [386.502196] ? irqentry_exit+0xf0/0x6d0 [386.502213] __x64_sys_ioctl+0x112/0x220 [386.502232] do_syscall_64+0xc3/0x430 [386.502253] entry_SYSCALL_64_after_hwframe+0x4b/0x53 [386.502269] RIP: 0033:0x7f62f7922fc9 [386.502351] [386.502357] INFO: task repro1:2072 blocked for more than 143 seconds. [386.502366] Not tainted 6.19.0-rc7 #4 [386.502373] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. [386.502378] task:repro1 state:D stack:28400 pid:2072 tgid:2072 ppid:294 2 [386.502427] Call Trace: [386.502431] [386.502439] __schedule+0x1198/0x3f00 [386.502463] ? io_schedule_timeout+0x80/0x80 [386.502483] ? mark_held_locks+0x50/0x80 [386.502505] rt_mutex_schedule+0x9f/0xe0 [386.502527] __rt_mutex_slowlock_locked.constprop.0+0xedc/0x30c0 [386.503218] ? down_write_trylock+0x1a0/0x1a0 [386.503246] ? lock_acquired+0xbd/0x340 [386.503269] rwbase_write_lock+0x744/0xa80 [386.503290] ? perf_fasync+0xc0/0x130 [386.503306] ? rt_mutex_adjust_prio_chain.isra.0+0x3240/0x3240 [386.503327] ? kvm_sched_clock_read+0x16/0x20 [386.503351] ? perf_fasync+0xc0/0x130 [386.503366] ? local_clock+0x10/0x20 [386.503386] ? lock_contended+0x189/0x420 [386.503407] down_write+0x6e/0x1e0 [386.503427] perf_fasync+0xc0/0x130 [386.503442] ? perf_cgroup_css_free+0x50/0x50 [386.503461] do_vfs_ioctl+0x9b9/0x1480 [386.503476] ? lock_vma_under_rcu+0x7ee/0xd90 [386.503493] ? ioctl_file_clone+0xf0/0xf0 [386.503508] ? lock_is_held_type+0xa0/0x110 [386.503524] ? handle_mm_fault+0x5a6/0x9d0 [386.503543] ? kvm_sched_clock_read+0x16/0x20 [386.504012] ? local_clock_noinstr+0xf/0xc0 [386.504049] ? exc_page_fault+0xb0/0x180 [386.504312] ? irqentry_exit+0xf0/0x6d0 [386.504330] __x64_sys_ioctl+0x112/0x220 [386.504369] entry_SYSCALL_64_after_hwframe+0x4b/0x53 [386.504464] [386.504470] INFO: task repro1:2073 blocked for more than 143 seconds. [386.504491] task:repro1 state:D stack:28400 pid:2073 tgid:2073 ppid:292 2 [386.504540] Call Trace: [386.504544] [386.505300] __schedule+0x1198/0x3f00 [386.505347] ? mark_held_locks+0x50/0x80 [386.505369] rt_mutex_schedule+0x9f/0xe0 [386.505391] __rt_mutex_slowlock_locked.constprop.0+0xedc/0x30c0 [386.505464] rwbase_write_lock+0x744/0xa80 [386.505988] down_write+0x6e/0x1e0 [386.506042] do_vfs_ioctl+0x9b9/0x1480 [386.506301] __x64_sys_ioctl+0x112/0x220 [386.506340] entry_SYSCALL_64_after_hwframe+0x4b/0x53 [386.506434] [386.506442] Showing all locks held in the system: [386.506447] 4 locks held by pr/legacy/16: [386.506456] 1 lock held by khungtaskd/37: [386.506464] #0: ffffffff85041540 (rcu_read_lock){....}-{1:3} [386.506503] 1 lock held by in:imklog/196: [386.506513] 1 lock held by repro1/2040: [386.506522] 1 lock held by repro1/2066: [386.506532] #0: ffff88800784bc50 (&sb->s_type->i_mutex_key#17) [386.507276] 1 lock held by repro1/2072: [386.507284] #0: ffff88800784bc50 (&sb->s_type->i_mutex_key#17) [386.507321] 1 lock held by repro1/2073: [386.507328] #0: ffff88800784bc50 (&sb->s_type->i_mutex_key#17) [427.459692] BUG: workqueue lockup - pool cpus=3D0 node=3D0 flags=3D0x0 nice=3D0 stuck for 40s! [427.459779] workqueue events: [427.459809] pending: vmstat_shepherd, e1000_watchdog [427.460020] workqueue events_freezable_pwr_efficient: [427.460020] in-flight: disk_events_workfn [427.460052] workqueue writeback: [427.460084] in-flight: wb_workfn [427.460231] Showing backtraces of running workers in stalled CPU-bound worker pools Message from syslogd@syzkaller at Feb 6 10:27:59 ... kernel:[ 427.459692] BUG: workqueue lockup - pool cpus=3D0 node=3D0 flags=3D0x0 nice=3D0 stuc! Thanks Zw Tang