From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 97B3438F62F; Wed, 29 Jul 2026 04:13:24 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785298405; cv=none; b=ea7x+1asmW0PtgJwJABflCGSkFuDXUTQ9bBS795OtWIxrWAxkFA/P52dmnwLCnKZtVHGUoqg6dSawV3b6rpJMIHYdMvo/U2Tybc9K3clwiaUgZaogfVeSTfiRIQOAs6dENFVymVoeRMuAsFivTr4ipSnSeO0pFqGbYgmtgYG1Oo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785298405; c=relaxed/simple; bh=llUZbqJSB0JbDZBg8VZC44vyriZEB6RFt7g4X8jyap4=; h=Date:To:From:Subject:Message-Id; b=gk6rl17QfrB/xt2fdADUdwjAglXcJPRzswvZ8L1P2E1pvFyKD1JQY8X+VzymDk7o6kO3JuRzsYQ9pnbwn+JAX1u/mKYc2Lh+TbVBP+/heePqJbjiJqFs6XrsIJ54g98Gtr5QcqFAfEZIC687RkwhTFp/Kbj6aZF6qMeLcWXMTBc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b=puxDdfs7; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="puxDdfs7" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5B5291F00A3A; Wed, 29 Jul 2026 04:13:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=korg; t=1785298404; bh=8Pw/Oeujj/Yuqg8vXUQpauKLXUeFvwG4J67tq4IjDeU=; h=Date:To:From:Subject; b=puxDdfs7O7FH3voBMnfjLA5Lkr4C6JCFu3AQbf8EOjpcSmXyHBp/irveHTOG0Ud0Y UquuxLCAsl4EMhCBOJI/hwqMyzwJUtNbE/0sQevtpOyuAisLWxMiUDaw1Fk/IOIaVw GfqxH4KJciZGDkE6ac1d25xpayZb2GvzgakS1UZY= Date: Tue, 28 Jul 2026 21:13:23 -0700 To: mm-commits@vger.kernel.org,stable@vger.kernel.org,sj@kernel.org,oleg@redhat.com,lance.yang@linux.dev,dave@stgolabs.net,catalin.marinas@arm.com,cai@lca.pw,leitao@debian.org,akpm@linux-foundation.org From: Andrew Morton Subject: [merged mm-stable] mm-kmemleak-avoid-soft-lockup-when-scanning-task-stacks.patch removed from -mm tree Message-Id: <20260729041324.5B5291F00A3A@smtp.kernel.org> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: The quilt patch titled Subject: mm/kmemleak: avoid soft lockup when scanning task stacks has been removed from the -mm tree. Its filename was mm-kmemleak-avoid-soft-lockup-when-scanning-task-stacks.patch This patch was dropped because it was merged into the mm-stable branch of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm ------------------------------------------------------ From: Breno Leitao Subject: mm/kmemleak: avoid soft lockup when scanning task stacks Date: Mon, 15 Jun 2026 10:49:06 -0700 Patch series "mm/kmemleak: avoid soft lockup when scanning task", v3. kmemleak_scan() scans every task stack under one rcu_read_lock() with no reschedule point, which can trip the soft lockup watchdog on hosts with very many threads. That prints the following message, depending on the workload+host configuration: watchdog: BUG: soft lockup - CPU#35 stuck for 22s! [kmemleak:537] scan_block kmemleak_scan kmemleak_scan_thread kthread Patch 1 walks the tasks with find_ge_pid() so the scan reschedules between tasks Patches 2-3 let the scan loops stop early once a scan is interrupted. This patch (of 3): kmemleak_scan() walks every thread and scans its kernel stack under a single rcu_read_lock() with no reschedule point. On a host with very many threads -- amplified by KASAN/lockdep in debug builds -- this loop can hog a CPU long enough to trip the soft lockup watchdog: watchdog: BUG: soft lockup - CPU#35 stuck for 22s! [kmemleak:537] scan_block kmemleak_scan kmemleak_scan_thread kthread A cond_resched() cannot be added directly: the loop runs inside an RCU read-side critical section. Walk the tasks one PID at a time with find_ge_pid(), taking the RCU read lock only to look up and pin each task. The stack is then scanned with no lock held, so cond_resched() runs between tasks and the scan stops early on scan_should_stop(). This follows the next_tgid()/task_seq_get_next() iteration pattern and keeps each RCU critical section short. Link: https://lore.kernel.org/20260615-kmemleak-stack-resched-v3-0-acecd7d7fd92@debian.org Link: https://lore.kernel.org/20260615-kmemleak-stack-resched-v3-1-acecd7d7fd92@debian.org Fixes: c4b28963fd79 ("mm/kmemleak: rely on rcu for task stack scanning") Signed-off-by: Breno Leitao Reviewed-by: Catalin Marinas Reviewed-by: Davidlohr Bueso Reviewed-by: Lance Yang Reviewed-by: Oleg Nesterov Cc: Qian Cai Cc: SeongJae Park Cc: Signed-off-by: Andrew Morton --- mm/kmemleak.c | 51 +++++++++++++++++++++++++++++++++++------------- 1 file changed, 38 insertions(+), 13 deletions(-) --- a/mm/kmemleak.c~mm-kmemleak-avoid-soft-lockup-when-scanning-task-stacks +++ a/mm/kmemleak.c @@ -1697,6 +1697,42 @@ unlock_put: } /* + * Scan all task kernel stacks, rescheduling between tasks. Each task is looked + * up and pinned within its own RCU read-side section, so no lock is held across + * the scan and the walk cannot trip the soft lockup watchdog. + */ +static void kmemleak_scan_task_stacks(void) +{ + struct pid *pid; + int nr = 1; + + do { + struct task_struct *p = NULL; + + rcu_read_lock(); + pid = find_ge_pid(nr, &init_pid_ns); + if (pid) { + nr = pid_nr(pid) + 1; + p = pid_task(pid, PIDTYPE_PID); + if (p) + get_task_struct(p); + } + rcu_read_unlock(); + + if (p) { + void *stack = try_get_task_stack(p); + + if (stack) { + scan_block(stack, stack + THREAD_SIZE, NULL); + put_task_stack(p); + } + put_task_struct(p); + } + cond_resched(); + } while (pid && !scan_should_stop()); +} + +/* * Print one leak inline. The hex dump is gated on OBJECT_ALLOCATED so it * does not touch user memory that was freed concurrently; the rest of the * report (backtrace, comm, pid) is always emitted since the kmemleak_object @@ -1885,19 +1921,8 @@ static void kmemleak_scan(void) /* * Scanning the task stacks (may introduce false negatives). */ - if (kmemleak_stack_scan) { - struct task_struct *p, *g; - - rcu_read_lock(); - for_each_process_thread(g, p) { - void *stack = try_get_task_stack(p); - if (stack) { - scan_block(stack, stack + THREAD_SIZE, NULL); - put_task_stack(p); - } - } - rcu_read_unlock(); - } + if (kmemleak_stack_scan) + kmemleak_scan_task_stacks(); /* * Scan the objects already referenced from the sections scanned _ Patches currently in -mm which might be from leitao@debian.org are mm-memory-failure-drop-dead-error_states-entry-for-reserved-pages.patch mm-memory-failure-surface-unhandlable-kernel-pages-as-enotrecoverable.patch mm-memory-failure-report-mf_msg_kernel-for-unrecoverable-kernel-pages.patch mm-memory-failure-add-panic-option-for-unrecoverable-pages.patch documentation-document-panic_on_unrecoverable_memory_failure-sysctl.patch radix-tree-fix-kmemleak-false-positives-on-tree-head-reassignment.patch mm-kmemleak-report-leaks-only-after-n-consecutive-unreferenced-scans.patch mm-kmemleak-factor-leak-confirmation-into-a-helper.patch selftests-mm-test-kmemleaks-n-consecutive-scan-leak-confirmation.patch mm-kmemleak-report-rcu-tasks-quiescent-states-during-the-scan.patch mm-migrate-report-rcu-tasks-quiescent-states-in-migrate_pages_batch.patch