From nobody Wed Nov 27 12:35:53 2024 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 90DC51A76D5; Wed, 9 Oct 2024 18:05:11 +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=1728497111; cv=none; b=eFzrkOpCmKrlNbkqVYhWNbMtWfausUd/zzT8RO6O7teV7EkeW/YiyHG31ott0+ppOZCFsKRYkllIXU1nCbgTYge0dp0ryn9KMzKjSfFf+szoTT0Qa97gN/qR5TlqGn/sCl2ELCZgSebayogvPQ3tLnMcVSTuGrLelSVaSrv/VmY= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1728497111; c=relaxed/simple; bh=7pa17iJCiaC6VrtPo21ztViCSaaHz8p6/8C7mQB27KI=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=ayd8s5HvmFCpThNWpSC58HY9ibTvuJdA6/GlkFY6dfsquUjH+xxDJHG0sI6hhqw9VxKVPy9QovG0VPA5YSJdmNIZHzWaiIRGRr40IAwU2NwmGmTGGD0xsUHdVsqJPCJhhEd37EnglHzb2kOYmqGkyZgwvsQOEU0F2/cpdbL4/9Q= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=EhO9iWqK; 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="EhO9iWqK" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3B71BC4CEC3; Wed, 9 Oct 2024 18:05:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1728497111; bh=7pa17iJCiaC6VrtPo21ztViCSaaHz8p6/8C7mQB27KI=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=EhO9iWqKYnQMV7d6GZR+LRUgHvwv/OQKi/SavZMii/Q7HjXAfkQSvk4xt/9wx6e6w u5DZrJOHUB8gS7cNIQM9r9Jr4A5NnZ6IHQ7Ab3oGS+g2V/Ij+0cUfCFELngn1oWrMv S9bnk+Dd1to7BfD7qCSD9+lNNYKykh5F42VJHJlBNRPyrtws7qiFnLuIr0Qnr3+YHt QKzmKlWIvGEzS9tpt580Iv/CQ6Ka0r1O+C0sN5GolQxeAhijpvFAOxF2OPsQumP1dZ 91zIiHej22Vvz7w5q68BsJDOTQr0KqzNNC/ROl6P91ad1Ezbs5Dm07CnHqWpv43SuA o5S99WKK2PXLw== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id EC9D3CE08E5; Wed, 9 Oct 2024 11:05:10 -0700 (PDT) From: "Paul E. McKenney" To: frederic@kernel.org, rcu@vger.kernel.org Cc: linux-kernel@vger.kernel.org, kernel-team@meta.com, rostedt@goodmis.org, "Paul E. McKenney" Subject: [PATCH rcu 1/3] rcu: Delete unused rcu_gp_might_be_stalled() function Date: Wed, 9 Oct 2024 11:05:07 -0700 Message-Id: <20241009180509.778133-1-paulmck@kernel.org> X-Mailer: git-send-email 2.40.1 In-Reply-To: References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" The rcu_gp_might_be_stalled() function is no longer used, so this commit removes it. Signed-off-by: Paul E. McKenney Reviewed-by: Joel Fernandes (Google) --- include/linux/rcutiny.h | 1 - include/linux/rcutree.h | 1 - kernel/rcu/tree_stall.h | 30 ------------------------------ 3 files changed, 32 deletions(-) diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h index 0ee270b3f5ed2..fe42315f667fc 100644 --- a/include/linux/rcutiny.h +++ b/include/linux/rcutiny.h @@ -165,7 +165,6 @@ static inline bool rcu_inkernel_boot_has_ended(void) { = return true; } static inline bool rcu_is_watching(void) { return true; } static inline void rcu_momentary_eqs(void) { } static inline void kfree_rcu_scheduler_running(void) { } -static inline bool rcu_gp_might_be_stalled(void) { return false; } =20 /* Avoid RCU read-side critical sections leaking across. */ static inline void rcu_all_qs(void) { barrier(); } diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h index 90a684f94776e..27d86d9127817 100644 --- a/include/linux/rcutree.h +++ b/include/linux/rcutree.h @@ -40,7 +40,6 @@ void kvfree_rcu_barrier(void); void rcu_barrier(void); void rcu_momentary_eqs(void); void kfree_rcu_scheduler_running(void); -bool rcu_gp_might_be_stalled(void); =20 struct rcu_gp_oldstate { unsigned long rgos_norm; diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h index 4432db6d0b99b..d7cdd535e50b1 100644 --- a/kernel/rcu/tree_stall.h +++ b/kernel/rcu/tree_stall.h @@ -76,36 +76,6 @@ int rcu_jiffies_till_stall_check(void) } EXPORT_SYMBOL_GPL(rcu_jiffies_till_stall_check); =20 -/** - * rcu_gp_might_be_stalled - Is it likely that the grace period is stalled? - * - * Returns @true if the current grace period is sufficiently old that - * it is reasonable to assume that it might be stalled. This can be - * useful when deciding whether to allocate memory to enable RCU-mediated - * freeing on the one hand or just invoking synchronize_rcu() on the other. - * The latter is preferable when the grace period is stalled. - * - * Note that sampling of the .gp_start and .gp_seq fields must be done - * carefully to avoid false positives at the beginnings and ends of - * grace periods. - */ -bool rcu_gp_might_be_stalled(void) -{ - unsigned long d =3D rcu_jiffies_till_stall_check() / RCU_STALL_MIGHT_DIV; - unsigned long j =3D jiffies; - - if (d < RCU_STALL_MIGHT_MIN) - d =3D RCU_STALL_MIGHT_MIN; - smp_mb(); // jiffies before .gp_seq to avoid false positives. - if (!rcu_gp_in_progress()) - return false; - // Long delays at this point avoids false positive, but a delay - // of ULONG_MAX/4 jiffies voids your no-false-positive warranty. - smp_mb(); // .gp_seq before second .gp_start - // And ditto here. - return !time_before(j, READ_ONCE(rcu_state.gp_start) + d); -} - /* Don't do RCU CPU stall warnings during long sysrq printouts. */ void rcu_sysrq_start(void) { --=20 2.40.1 From nobody Wed Nov 27 12:35:53 2024 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 90E1A1DEFCE; Wed, 9 Oct 2024 18:05:11 +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=1728497111; cv=none; b=TEmoAgrQE1sRCr9dHy+yVChJofxetndKihZJafVvqXZVdamp9EBovGV8YDyVCr6cmMmnTGcNg6Cp+xmS995Fyjnh1UhIKk2Zbxd0s/VHiEouOBYfZbksfeVUqPq42eZlabuS1QsCtaFSS3KWBpOghYcnS0X0/DZDUaP/YRjJAN4= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1728497111; c=relaxed/simple; bh=36w1sLkGTystT8QKSFmDo6WwK0sm86D4acqxrcVO96I=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=Eo+Asd/B90H5eotMTmZZPegxlV3QnnAv1VuMPdQLdRzhd3xAnYbVtz6U0lkDSohCzoNlCz/UUjNE2CYiJsUgfBEkPBBOU8+JuQx9cy7eroM3js2laGhRIHVxvkB11W3GKN30DbHv7MiVMsHXvnl573WMVud7nuUYiNpQzfiJymU= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=tpuY5n88; 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="tpuY5n88" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4F7CEC4CECC; Wed, 9 Oct 2024 18:05:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1728497111; bh=36w1sLkGTystT8QKSFmDo6WwK0sm86D4acqxrcVO96I=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=tpuY5n889I+dtV8LsUtX7+9lDFdvqD47WRXhGQ0kgXn1lz39zCKJ0TYBM1yUA0DGN Sub6OjB9pPxLFy9vCZfbv9DOZ6M/nuqnnz3j3WkrS/y+1M8CIpfMIFsRv0sKXxGQkh icD2eXMdQ4gCyow/XLzAecX8ChX+araKkFPmFJR1mbmoDLV8hQi0m0kFUn+1acTxox Fcs73xOVvxsagW1NIm6/3unVKEQtPXX/OUUGPqfZhJXLIrMg/Vla+IG1Y6qvfjGWxH oMpd0B1R0NtcKffJh2XfC8ELNxTk5wSjQds7LdNEAP9ACf8wv9yw1TrYWXqUPH+WsW fAxb8VSQWHhDQ== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id EFC3ECE0B68; Wed, 9 Oct 2024 11:05:10 -0700 (PDT) From: "Paul E. McKenney" To: frederic@kernel.org, rcu@vger.kernel.org Cc: linux-kernel@vger.kernel.org, kernel-team@meta.com, rostedt@goodmis.org, "Paul E. McKenney" Subject: [PATCH rcu 2/3] rcu: Stop stall warning from dumping stacks if grace period ends Date: Wed, 9 Oct 2024 11:05:08 -0700 Message-Id: <20241009180509.778133-2-paulmck@kernel.org> X-Mailer: git-send-email 2.40.1 In-Reply-To: References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Currently, once an RCU CPU stall warning decides to dump the stalling CPUs' stacks, the rcu_dump_cpu_stacks() function persists until it has gone through the full list. Unfortunately, if the stalled grace periods ends midway through, this function will be dumping stacks of innocent-bystander CPUs that happen to be blocking not the old grace period, but instead the new one. This can cause serious confusion. This commit therefore stops dumping stacks if and when the stalled grace period ends. Signed-off-by: Paul E. McKenney Reviewed-by: Joel Fernandes (Google) --- kernel/rcu/tree_stall.h | 17 +++++++++++------ 1 file changed, 11 insertions(+), 6 deletions(-) diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h index d7cdd535e50b1..9d79133377ff6 100644 --- a/kernel/rcu/tree_stall.h +++ b/kernel/rcu/tree_stall.h @@ -335,13 +335,17 @@ static int rcu_print_task_stall(struct rcu_node *rnp,= unsigned long flags) * that don't support NMI-based stack dumps. The NMI-triggered stack * traces are more accurate because they are printed by the target CPU. */ -static void rcu_dump_cpu_stacks(void) +static void rcu_dump_cpu_stacks(unsigned long gp_seq) { int cpu; unsigned long flags; struct rcu_node *rnp; =20 rcu_for_each_leaf_node(rnp) { + if (gp_seq !=3D rcu_state.gp_seq) { + pr_err("INFO: Stall ended during stack backtracing.\n"); + return; + } printk_deferred_enter(); raw_spin_lock_irqsave_rcu_node(rnp, flags); for_each_leaf_node_possible_cpu(rnp, cpu) @@ -608,7 +612,7 @@ static void print_other_cpu_stall(unsigned long gp_seq,= unsigned long gps) (long)rcu_seq_current(&rcu_state.gp_seq), totqlen, data_race(rcu_state.n_online_cpus)); // Diagnostic read if (ndetected) { - rcu_dump_cpu_stacks(); + rcu_dump_cpu_stacks(gp_seq); =20 /* Complain about tasks blocking the grace period. */ rcu_for_each_leaf_node(rnp) @@ -640,7 +644,7 @@ static void print_other_cpu_stall(unsigned long gp_seq,= unsigned long gps) rcu_force_quiescent_state(); /* Kick them all. */ } =20 -static void print_cpu_stall(unsigned long gps) +static void print_cpu_stall(unsigned long gp_seq, unsigned long gps) { int cpu; unsigned long flags; @@ -677,7 +681,7 @@ static void print_cpu_stall(unsigned long gps) rcu_check_gp_kthread_expired_fqs_timer(); rcu_check_gp_kthread_starvation(); =20 - rcu_dump_cpu_stacks(); + rcu_dump_cpu_stacks(gp_seq); =20 raw_spin_lock_irqsave_rcu_node(rnp, flags); /* Rewrite if needed in case of slow consoles. */ @@ -759,7 +763,8 @@ static void check_cpu_stall(struct rcu_data *rdp) gs2 =3D READ_ONCE(rcu_state.gp_seq); if (gs1 !=3D gs2 || ULONG_CMP_LT(j, js) || - ULONG_CMP_GE(gps, js)) + ULONG_CMP_GE(gps, js) || + !rcu_seq_state(gs2)) return; /* No stall or GP completed since entering function. */ rnp =3D rdp->mynode; jn =3D jiffies + ULONG_MAX / 2; @@ -780,7 +785,7 @@ static void check_cpu_stall(struct rcu_data *rdp) pr_err("INFO: %s detected stall, but suppressed full report due to a st= uck CSD-lock.\n", rcu_state.name); } else if (self_detected) { /* We haven't checked in, so go dump stack. */ - print_cpu_stall(gps); + print_cpu_stall(gs2, gps); } else { /* They had a few time units to dump stack, so complain. */ print_other_cpu_stall(gs2, gps); --=20 2.40.1 From nobody Wed Nov 27 12:35:53 2024 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 C18FF19DF66; Wed, 9 Oct 2024 18:05:11 +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=1728497111; cv=none; b=Qw6KwTB+gux4dGwFYMMUZYYoLPl1hk8iVtQAAP1QQIz2VmJHKQUbuxmL8+rbrFpZF+mVh/QglLtTQ6u5KuZlD83RixYkxwdiUEy56RqOi8i0q5TtUN19tb6R2t4mbdMOTVo4Lehw/+j5cDtkvnNmWSuPuoiqzqH+sOFfQ1a7T/g= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1728497111; c=relaxed/simple; bh=LXGw5NZfIRWF05WERyYwMt48zLZsjeoEitaRbfqAzcI=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=gu25mGNqOv5eqhctsXWHsd5oA603TUSQKIO16FP1oMk5vBFqnpJ1Zpz+f3vsGT+APhxofPTaGVbSSJ/nlSzof1nPNa9e9VuWMAfUMvrORudWtN6W42PO6bJVJqzFZfuHkB1FO1BGlwhXKF4tQ/1ksU37oYva/fD9G/4rRvuBl0c= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=c2H09bcq; 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="c2H09bcq" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5A051C4CECF; Wed, 9 Oct 2024 18:05:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1728497111; bh=LXGw5NZfIRWF05WERyYwMt48zLZsjeoEitaRbfqAzcI=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=c2H09bcquVszeNTbbwLGvSRoTwW5NnJAkcpb8ZXUJA0IHbjvKgY3310QyyONKr+dq 4WYyZQIjbN/yq23dNmfr4lRC/XTojre+vsa37/zMN8MSI97UHczXq21VmwdU4u4DTb j8RXIb3mBQAxONX2px8eIoYSt35K17bWjsaRMFHx+4ttZ/kG6rnsV7XCggtcgEgO5b 4j4ptCTvyhjIIzgUN6LNqnDyc4pnP7j/qVwRrBKpMAt6WHqcNgyBTs9Sr1J+IuJAUY aoiNv9n9+pbyWM0lLyjq5TY7Xd27FirsABBFmgWpRu57Y1ZXXA0qcKqFoqjHJcZI7h sP1nIQEr/8sOw== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id F2DC8CE0BB1; Wed, 9 Oct 2024 11:05:10 -0700 (PDT) From: "Paul E. McKenney" To: frederic@kernel.org, rcu@vger.kernel.org Cc: linux-kernel@vger.kernel.org, kernel-team@meta.com, rostedt@goodmis.org, "Paul E. McKenney" Subject: [PATCH rcu 3/3] rcu: Finer-grained grace-period-end checks in rcu_dump_cpu_stacks() Date: Wed, 9 Oct 2024 11:05:09 -0700 Message-Id: <20241009180509.778133-3-paulmck@kernel.org> X-Mailer: git-send-email 2.40.1 In-Reply-To: References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" This commit pushes the grace-period-end checks further down into rcu_dump_cpu_stacks(), and also uses lockless checks coupled with finer-grained locking. The result is that the current leaf rcu_node structure's ->lock is acquired only if a stack backtrace might be needed from the current CPU, and is held across only that CPU's backtrace. As a result, if there are no stalled CPUs associated with a given rcu_node structure, then its ->lock will not be acquired at all. On large systems, it is usually (though not always) the case that a small number of CPUs are stalling the current grace period, which means that the ->lock need be acquired only for a small fraction of the rcu_node structures. Signed-off-by: Paul E. McKenney Reviewed-by: Joel Fernandes (Google) --- kernel/rcu/tree_stall.h | 18 +++++++++++------- 1 file changed, 11 insertions(+), 7 deletions(-) diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h index 9d79133377ff6..8994391b95c76 100644 --- a/kernel/rcu/tree_stall.h +++ b/kernel/rcu/tree_stall.h @@ -342,20 +342,24 @@ static void rcu_dump_cpu_stacks(unsigned long gp_seq) struct rcu_node *rnp; =20 rcu_for_each_leaf_node(rnp) { - if (gp_seq !=3D rcu_state.gp_seq) { - pr_err("INFO: Stall ended during stack backtracing.\n"); - return; - } printk_deferred_enter(); - raw_spin_lock_irqsave_rcu_node(rnp, flags); - for_each_leaf_node_possible_cpu(rnp, cpu) + for_each_leaf_node_possible_cpu(rnp, cpu) { + if (gp_seq !=3D data_race(rcu_state.gp_seq)) { + printk_deferred_exit(); + pr_err("INFO: Stall ended during stack backtracing.\n"); + return; + } + if (!(data_race(rnp->qsmask) & leaf_node_cpu_bit(rnp, cpu))) + continue; + raw_spin_lock_irqsave_rcu_node(rnp, flags); if (rnp->qsmask & leaf_node_cpu_bit(rnp, cpu)) { if (cpu_is_offline(cpu)) pr_err("Offline CPU %d blocking current GP.\n", cpu); else dump_cpu_task(cpu); + raw_spin_unlock_irqrestore_rcu_node(rnp, flags); } - raw_spin_unlock_irqrestore_rcu_node(rnp, flags); + } printk_deferred_exit(); } } --=20 2.40.1