From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 121AA3446B0 for ; Sat, 28 Feb 2026 18:07:18 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772302038; cv=none; b=QqaFF9I8UVQBHd/iZzVagYvWDjVkC8y47Zt4y0AN4jbYIbmIN/HIM4pkPdL3rW+49BJBCapr5NliwzmKX+N3IVlAozduNseqXBLVYgMhEYn2djaI5eSyDkO9wHfQWYVh1vWy8wtdZ7/MnEGBQrqzkiwpXysWH2LSZf9YZZvT70c= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772302038; c=relaxed/simple; bh=gAbmGD033n4QaDbS640GbtA8BEWZy2zAHBqTWV524Z4=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=HGPX+hSk3PLC52v5n3gOZy+E0ZM+CRisG4ApNtZFaXTMOv99F+ZVXcsQ2n90yJYGT/fChcEV/MYUgNeKe6s5EcuEV+IjJQwNa3utVj3n1cglhNGHNCXyqvJ0KD8h4mRtavKa82aqUbgKiaa5lEUf+TQ59EC4lA/7LhUNYuCpmUA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=mSnq/H3j; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="mSnq/H3j" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 35765C19423; Sat, 28 Feb 2026 18:07:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1772302038; bh=gAbmGD033n4QaDbS640GbtA8BEWZy2zAHBqTWV524Z4=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=mSnq/H3j2YPAbxpfUDDRA0d5IiBvxkv6CNk3oeleZtYQeL/vteSMc0ly0Hc8vbKbK xyV0eSXouFvxRCh0i2B0poiHrjgqjmnbkckwN9I5UpPSbpqNsN5wCaQk81Wa+xXO+/ NT8aixWXu873y0XVN7XHmPJZJ+gkoQ5JsxVP2hr+WXBC4Cw/BF5SokK6boB4eIsm6t qMK2/HaYlPnskfA+Pw3lxb+Wj+xrhTQm1dGf8+PAVL53JDa7lqMp1Pz5WlRcOugNH9 H71pUygXnHzy4P1u0mgswV/l1AwUFNym++4TGobJXLd/GNNk5GTH2ZmYd61ohLPV40 bOST6nKO3nWsg== From: Sasha Levin To: patches@lists.linux.dev Cc: Yao Kai , Tengda Wu , Joel Fernandes , "Paul E. McKenney" , Boqun Feng , Sasha Levin Subject: [PATCH 6.6 009/283] rcu: Fix rcu_read_unlock() deadloop due to softirq Date: Sat, 28 Feb 2026 13:02:31 -0500 Message-ID: <20260228180709.1583486-9-sashal@kernel.org> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20260228180709.1583486-1-sashal@kernel.org> References: <20260228180709.1583486-1-sashal@kernel.org> Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore Content-Transfer-Encoding: 8bit From: Yao Kai [ Upstream commit d41e37f26b3157b3f1d10223863519a943aa239b ] Commit 5f5fa7ea89dc ("rcu: Don't use negative nesting depth in __rcu_read_unlock()") removes the recursion-protection code from __rcu_read_unlock(). Therefore, we could invoke the deadloop in raise_softirq_irqoff() with ftrace enabled as follows: WARNING: CPU: 0 PID: 0 at kernel/trace/trace.c:3021 __ftrace_trace_stack.constprop.0+0x172/0x180 Modules linked in: my_irq_work(O) CPU: 0 UID: 0 PID: 0 Comm: swapper/0 Tainted: G O 6.18.0-rc7-dirty #23 PREEMPT(full) Tainted: [O]=OOT_MODULE Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014 RIP: 0010:__ftrace_trace_stack.constprop.0+0x172/0x180 RSP: 0018:ffffc900000034a8 EFLAGS: 00010002 RAX: 0000000000000000 RBX: 0000000000000004 RCX: 0000000000000000 RDX: 0000000000000003 RSI: ffffffff826d7b87 RDI: ffffffff826e9329 RBP: 0000000000090009 R08: 0000000000000005 R09: ffffffff82afbc4c R10: 0000000000000008 R11: 0000000000011d7a R12: 0000000000000000 R13: ffff888003874100 R14: 0000000000000003 R15: ffff8880038c1054 FS: 0000000000000000(0000) GS:ffff8880fa8ea000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 000055b31fa7f540 CR3: 00000000078f4005 CR4: 0000000000770ef0 PKRU: 55555554 Call Trace: trace_buffer_unlock_commit_regs+0x6d/0x220 trace_event_buffer_commit+0x5c/0x260 trace_event_raw_event_softirq+0x47/0x80 raise_softirq_irqoff+0x6e/0xa0 rcu_read_unlock_special+0xb1/0x160 unwind_next_frame+0x203/0x9b0 __unwind_start+0x15d/0x1c0 arch_stack_walk+0x62/0xf0 stack_trace_save+0x48/0x70 __ftrace_trace_stack.constprop.0+0x144/0x180 trace_buffer_unlock_commit_regs+0x6d/0x220 trace_event_buffer_commit+0x5c/0x260 trace_event_raw_event_softirq+0x47/0x80 raise_softirq_irqoff+0x6e/0xa0 rcu_read_unlock_special+0xb1/0x160 unwind_next_frame+0x203/0x9b0 __unwind_start+0x15d/0x1c0 arch_stack_walk+0x62/0xf0 stack_trace_save+0x48/0x70 __ftrace_trace_stack.constprop.0+0x144/0x180 trace_buffer_unlock_commit_regs+0x6d/0x220 trace_event_buffer_commit+0x5c/0x260 trace_event_raw_event_softirq+0x47/0x80 raise_softirq_irqoff+0x6e/0xa0 rcu_read_unlock_special+0xb1/0x160 unwind_next_frame+0x203/0x9b0 __unwind_start+0x15d/0x1c0 arch_stack_walk+0x62/0xf0 stack_trace_save+0x48/0x70 __ftrace_trace_stack.constprop.0+0x144/0x180 trace_buffer_unlock_commit_regs+0x6d/0x220 trace_event_buffer_commit+0x5c/0x260 trace_event_raw_event_softirq+0x47/0x80 raise_softirq_irqoff+0x6e/0xa0 rcu_read_unlock_special+0xb1/0x160 __is_insn_slot_addr+0x54/0x70 kernel_text_address+0x48/0xc0 __kernel_text_address+0xd/0x40 unwind_get_return_address+0x1e/0x40 arch_stack_walk+0x9c/0xf0 stack_trace_save+0x48/0x70 __ftrace_trace_stack.constprop.0+0x144/0x180 trace_buffer_unlock_commit_regs+0x6d/0x220 trace_event_buffer_commit+0x5c/0x260 trace_event_raw_event_softirq+0x47/0x80 __raise_softirq_irqoff+0x61/0x80 __flush_smp_call_function_queue+0x115/0x420 __sysvec_call_function_single+0x17/0xb0 sysvec_call_function_single+0x8c/0xc0 Commit b41642c87716 ("rcu: Fix rcu_read_unlock() deadloop due to IRQ work") fixed the infinite loop in rcu_read_unlock_special() for IRQ work by setting a flag before calling irq_work_queue_on(). We fix this issue by setting the same flag before calling raise_softirq_irqoff() and rename the flag to defer_qs_pending for more common. Fixes: 5f5fa7ea89dc ("rcu: Don't use negative nesting depth in __rcu_read_unlock()") Reported-by: Tengda Wu Signed-off-by: Yao Kai Reviewed-by: Joel Fernandes Tested-by: Paul E. McKenney Signed-off-by: Joel Fernandes Signed-off-by: Boqun Feng Signed-off-by: Sasha Levin --- kernel/rcu/tree.h | 2 +- kernel/rcu/tree_plugin.h | 15 +++++++++------ 2 files changed, 10 insertions(+), 7 deletions(-) diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h index f8408e7a5f824..b79599b2059cc 100644 --- a/kernel/rcu/tree.h +++ b/kernel/rcu/tree.h @@ -203,7 +203,7 @@ struct rcu_data { /* during and after the last grace */ /* period it is aware of. */ struct irq_work defer_qs_iw; /* Obtain later scheduler attention. */ - int defer_qs_iw_pending; /* Scheduler attention pending? */ + int defer_qs_pending; /* irqwork or softirq pending? */ struct work_struct strict_work; /* Schedule readers for strict GPs. */ /* 2) batch handling */ diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index 04044b492cc31..8cf1adcd259ba 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -475,8 +475,8 @@ rcu_preempt_deferred_qs_irqrestore(struct task_struct *t, unsigned long flags) union rcu_special special; rdp = this_cpu_ptr(&rcu_data); - if (rdp->defer_qs_iw_pending == DEFER_QS_PENDING) - rdp->defer_qs_iw_pending = DEFER_QS_IDLE; + if (rdp->defer_qs_pending == DEFER_QS_PENDING) + rdp->defer_qs_pending = DEFER_QS_IDLE; /* * If RCU core is waiting for this CPU to exit its critical section, @@ -634,7 +634,7 @@ static void rcu_preempt_deferred_qs_handler(struct irq_work *iwp) * 5. Deferred QS reporting does not happen. */ if (rcu_preempt_depth() > 0) - WRITE_ONCE(rdp->defer_qs_iw_pending, DEFER_QS_IDLE); + WRITE_ONCE(rdp->defer_qs_pending, DEFER_QS_IDLE); } /* @@ -736,7 +736,10 @@ static void rcu_read_unlock_special(struct task_struct *t) // Using softirq, safe to awaken, and either the // wakeup is free or there is either an expedited // GP in flight or a potential need to deboost. - raise_softirq_irqoff(RCU_SOFTIRQ); + if (rdp->defer_qs_pending != DEFER_QS_PENDING) { + rdp->defer_qs_pending = DEFER_QS_PENDING; + raise_softirq_irqoff(RCU_SOFTIRQ); + } } else { // Enabling BH or preempt does reschedule, so... // Also if no expediting and no possible deboosting, @@ -745,11 +748,11 @@ static void rcu_read_unlock_special(struct task_struct *t) set_tsk_need_resched(current); set_preempt_need_resched(); if (IS_ENABLED(CONFIG_IRQ_WORK) && irqs_were_disabled && - needs_exp && rdp->defer_qs_iw_pending != DEFER_QS_PENDING && + needs_exp && rdp->defer_qs_pending != DEFER_QS_PENDING && cpu_online(rdp->cpu)) { // Get scheduler to re-evaluate and call hooks. // If !IRQ_WORK, FQS scan will eventually IPI. - rdp->defer_qs_iw_pending = DEFER_QS_PENDING; + rdp->defer_qs_pending = DEFER_QS_PENDING; irq_work_queue_on(&rdp->defer_qs_iw, rdp->cpu); } } -- 2.51.0