Hi Stephen
On Fri, Aug 09, 2024 at 12:23:21PM +1000, Stephen Rothwell wrote:
> Hi all,
>
> Today's linux-next merge of the rcu tree got a conflict in:
>
> kernel/rcu/tree_exp.h
>
> between commit:
>
> 9a30ceb4d93e ("rcu: Mark emergency sections in rcu stalls")
>
> from the printk tree and commits:
>
> 34863005f96e ("rcu: Extract synchronize_rcu_expedited_stall() from synchronize_rcu_expedited_wait()")
> c925e2f61399 ("rcu: Let dump_cpu_task() be used without preemption disabled")
>
> from the rcu tree.
>
> I fixed it up (I think - see below) and can carry the fix as
> necessary. This is now fixed as far as linux-next is concerned, but any
> non trivial conflicts should be mentioned to your upstream maintainer
> when your tree is submitted for merging. You may also want to consider
> cooperating with the maintainer of the conflicting tree to minimise any
> particularly complex conflicts.
>
Thank you! The resolution looks good to me. I will mention this conflict
during PR submission and coordinate with the maintainer of the printk
tree.
- Neeraj
> --
> Cheers,
> Stephen Rothwell
>
> diff --cc kernel/rcu/tree_exp.h
> index be2d251e84f8,c3266bf709d5..000000000000
> --- a/kernel/rcu/tree_exp.h
> +++ b/kernel/rcu/tree_exp.h
> @@@ -543,6 -542,67 +543,68 @@@ static bool synchronize_rcu_expedited_w
> return false;
> }
>
> + /*
> + * Print out an expedited RCU CPU stall warning message.
> + */
> + static void synchronize_rcu_expedited_stall(unsigned long jiffies_start, unsigned long j)
> + {
> + int cpu;
> + unsigned long mask;
> + int ndetected;
> + struct rcu_node *rnp;
> + struct rcu_node *rnp_root = rcu_get_root();
> +
> + if (READ_ONCE(csd_lock_suppress_rcu_stall) && csd_lock_is_stuck()) {
> + pr_err("INFO: %s detected expedited stalls, but suppressed full report due to a stuck CSD-lock.\n", rcu_state.name);
> + return;
> + }
> + pr_err("INFO: %s detected expedited stalls on CPUs/tasks: {", rcu_state.name);
> + ndetected = 0;
> + rcu_for_each_leaf_node(rnp) {
> + ndetected += rcu_print_task_exp_stall(rnp);
> + for_each_leaf_node_possible_cpu(rnp, cpu) {
> + struct rcu_data *rdp;
> +
> + mask = leaf_node_cpu_bit(rnp, cpu);
> + if (!(READ_ONCE(rnp->expmask) & mask))
> + continue;
> + ndetected++;
> + rdp = per_cpu_ptr(&rcu_data, cpu);
> + pr_cont(" %d-%c%c%c%c", cpu,
> + "O."[!!cpu_online(cpu)],
> + "o."[!!(rdp->grpmask & rnp->expmaskinit)],
> + "N."[!!(rdp->grpmask & rnp->expmaskinitnext)],
> + "D."[!!data_race(rdp->cpu_no_qs.b.exp)]);
> + }
> + }
> + pr_cont(" } %lu jiffies s: %lu root: %#lx/%c\n",
> + j - jiffies_start, rcu_state.expedited_sequence, data_race(rnp_root->expmask),
> + ".T"[!!data_race(rnp_root->exp_tasks)]);
> + if (ndetected) {
> + pr_err("blocking rcu_node structures (internal RCU debug):");
> + rcu_for_each_node_breadth_first(rnp) {
> + if (rnp == rnp_root)
> + continue; /* printed unconditionally */
> + if (sync_rcu_exp_done_unlocked(rnp))
> + continue;
> + pr_cont(" l=%u:%d-%d:%#lx/%c",
> + rnp->level, rnp->grplo, rnp->grphi, data_race(rnp->expmask),
> + ".T"[!!data_race(rnp->exp_tasks)]);
> + }
> + pr_cont("\n");
> + }
> + rcu_for_each_leaf_node(rnp) {
> + for_each_leaf_node_possible_cpu(rnp, cpu) {
> + mask = leaf_node_cpu_bit(rnp, cpu);
> + if (!(READ_ONCE(rnp->expmask) & mask))
> + continue;
> + dump_cpu_task(cpu);
> ++ nbcon_cpu_emergency_flush();
> + }
> + rcu_exp_print_detail_task_stall_rnp(rnp);
> + }
> + }
> +
> /*
> * Wait for the expedited grace period to elapse, issuing any needed
> * RCU CPU stall warnings along the way.
> @@@ -597,60 -652,8 +657,11 @@@ static void synchronize_rcu_expedited_w
> j = jiffies;
> rcu_stall_notifier_call_chain(RCU_STALL_NOTIFY_EXP, (void *)(j - jiffies_start));
> trace_rcu_stall_warning(rcu_state.name, TPS("ExpeditedStall"));
> - pr_err("INFO: %s detected expedited stalls on CPUs/tasks: {",
> - rcu_state.name);
> - ndetected = 0;
> - rcu_for_each_leaf_node(rnp) {
> - ndetected += rcu_print_task_exp_stall(rnp);
> - for_each_leaf_node_possible_cpu(rnp, cpu) {
> - struct rcu_data *rdp;
> -
> - mask = leaf_node_cpu_bit(rnp, cpu);
> - if (!(READ_ONCE(rnp->expmask) & mask))
> - continue;
> - ndetected++;
> - rdp = per_cpu_ptr(&rcu_data, cpu);
> - pr_cont(" %d-%c%c%c%c", cpu,
> - "O."[!!cpu_online(cpu)],
> - "o."[!!(rdp->grpmask & rnp->expmaskinit)],
> - "N."[!!(rdp->grpmask & rnp->expmaskinitnext)],
> - "D."[!!data_race(rdp->cpu_no_qs.b.exp)]);
> - }
> - }
> - pr_cont(" } %lu jiffies s: %lu root: %#lx/%c\n",
> - j - jiffies_start, rcu_state.expedited_sequence,
> - data_race(rnp_root->expmask),
> - ".T"[!!data_race(rnp_root->exp_tasks)]);
> - if (ndetected) {
> - pr_err("blocking rcu_node structures (internal RCU debug):");
> - rcu_for_each_node_breadth_first(rnp) {
> - if (rnp == rnp_root)
> - continue; /* printed unconditionally */
> - if (sync_rcu_exp_done_unlocked(rnp))
> - continue;
> - pr_cont(" l=%u:%d-%d:%#lx/%c",
> - rnp->level, rnp->grplo, rnp->grphi,
> - data_race(rnp->expmask),
> - ".T"[!!data_race(rnp->exp_tasks)]);
> - }
> - pr_cont("\n");
> - }
> - rcu_for_each_leaf_node(rnp) {
> - for_each_leaf_node_possible_cpu(rnp, cpu) {
> - mask = leaf_node_cpu_bit(rnp, cpu);
> - if (!(READ_ONCE(rnp->expmask) & mask))
> - continue;
> - preempt_disable(); // For smp_processor_id() in dump_cpu_task().
> - dump_cpu_task(cpu);
> - preempt_enable();
> - nbcon_cpu_emergency_flush();
> - }
> - rcu_exp_print_detail_task_stall_rnp(rnp);
> - }
> + synchronize_rcu_expedited_stall(jiffies_start, j);
> jiffies_stall = 3 * rcu_exp_jiffies_till_stall_check() + 3;
> +
> + nbcon_cpu_emergency_exit();
> +
> panic_on_rcu_stall();
> }
> }
