commit 994f706872e6 ("srcu: Make Tree SRCU able to operate without
snp_node array") assumes that cpu 0 is always online, but that is not
the truth when using maxcpus=1 in the command line for the kdump kernel.
On a PowerPC, the following kdump kernel hanging is observed:
...
[ 1.740036] systemd[1]: Hostname set to <xyz.com>
[ 243.686240] INFO: task systemd:1 blocked for more than 122 seconds.
[ 243.686264] Not tainted 6.1.0-rc1 #1
[ 243.686272] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[ 243.686281] task:systemd state:D stack:0 pid:1 ppid:0 flags:0x00042000
[ 243.686296] Call Trace:
[ 243.686301] [c000000016657640] [c000000016657670] 0xc000000016657670 (unreliable)
[ 243.686317] [c000000016657830] [c00000001001dec0] __switch_to+0x130/0x220
[ 243.686333] [c000000016657890] [c000000010f607b8] __schedule+0x1f8/0x580
[ 243.686347] [c000000016657940] [c000000010f60bb4] schedule+0x74/0x140
[ 243.686361] [c0000000166579b0] [c000000010f699b8] schedule_timeout+0x168/0x1c0
[ 243.686374] [c000000016657a80] [c000000010f61de8] __wait_for_common+0x148/0x360
[ 243.686387] [c000000016657b20] [c000000010176bb0] __flush_work.isra.0+0x1c0/0x3d0
[ 243.686401] [c000000016657bb0] [c0000000105f2768] fsnotify_wait_marks_destroyed+0x28/0x40
[ 243.686415] [c000000016657bd0] [c0000000105f21b8] fsnotify_destroy_group+0x68/0x160
[ 243.686428] [c000000016657c40] [c0000000105f6500] inotify_release+0x30/0xa0
[ 243.686440] [c000000016657cb0] [c0000000105751a8] __fput+0xc8/0x350
[ 243.686452] [c000000016657d00] [c00000001017d524] task_work_run+0xe4/0x170
[ 243.686464] [c000000016657d50] [c000000010020e94] do_notify_resume+0x134/0x140
[ 243.686478] [c000000016657d80] [c00000001002eb18] interrupt_exit_user_prepare_main+0x198/0x270
[ 243.686493] [c000000016657de0] [c00000001002ec60] syscall_exit_prepare+0x70/0x180
[ 243.686505] [c000000016657e10] [c00000001000bf7c] system_call_vectored_common+0xfc/0x280
[ 243.686520] --- interrupt: 3000 at 0x7fffa47d5ba4
[ 243.686528] NIP: 00007fffa47d5ba4 LR: 0000000000000000 CTR: 0000000000000000
[ 243.686538] REGS: c000000016657e80 TRAP: 3000 Not tainted (6.1.0-rc1)
[ 243.686548] MSR: 800000000000d033 <SF,EE,PR,ME,IR,DR,RI,LE> CR: 42044440 XER: 00000000
[ 243.686572] IRQMASK: 0
[ 243.686572] GPR00: 0000000000000006 00007ffffa606710 00007fffa48e7200 0000000000000000
[ 243.686572] GPR04: 0000000000000002 000000000000000a 0000000000000000 0000000000000001
[ 243.686572] GPR08: 000001000c172dd0 0000000000000000 0000000000000000 0000000000000000
[ 243.686572] GPR12: 0000000000000000 00007fffa4ff4bc0 0000000000000000 0000000000000000
[ 243.686572] GPR16: 0000000000000000 0000000000000000 0000000000000000 0000000000000000
[ 243.686572] GPR20: 0000000132dfdc50 000000000000000e 0000000000189375 0000000000000000
[ 243.686572] GPR24: 00007ffffa606ae0 0000000000000005 000001000c185490 000001000c172570
[ 243.686572] GPR28: 000001000c172990 000001000c184850 000001000c172e00 00007fffa4fedd98
[ 243.686683] NIP [00007fffa47d5ba4] 0x7fffa47d5ba4
[ 243.686691] LR [0000000000000000] 0x0
[ 243.686698] --- interrupt: 3000
[ 243.686708] INFO: task kworker/u16:1:24 blocked for more than 122 seconds.
[ 243.686717] Not tainted 6.1.0-rc1 #1
[ 243.686724] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[ 243.686733] task:kworker/u16:1 state:D stack:0 pid:24 ppid:2 flags:0x00000800
[ 243.686747] Workqueue: events_unbound fsnotify_mark_destroy_workfn
[ 243.686758] Call Trace:
[ 243.686762] [c0000000166736e0] [c00000004fd91000] 0xc00000004fd91000 (unreliable)
[ 243.686775] [c0000000166738d0] [c00000001001dec0] __switch_to+0x130/0x220
[ 243.686788] [c000000016673930] [c000000010f607b8] __schedule+0x1f8/0x580
[ 243.686801] [c0000000166739e0] [c000000010f60bb4] schedule+0x74/0x140
[ 243.686814] [c000000016673a50] [c000000010f699b8] schedule_timeout+0x168/0x1c0
[ 243.686827] [c000000016673b20] [c000000010f61de8] __wait_for_common+0x148/0x360
[ 243.686840] [c000000016673bc0] [c000000010210840] __synchronize_srcu.part.0+0xa0/0xe0
[ 243.686855] [c000000016673c30] [c0000000105f2c64] fsnotify_mark_destroy_workfn+0xc4/0x1a0
[ 243.686868] [c000000016673ca0] [c000000010174ea8] process_one_work+0x2a8/0x570
[ 243.686882] [c000000016673d40] [c000000010175208] worker_thread+0x98/0x5e0
[ 243.686895] [c000000016673dc0] [c0000000101828d4] kthread+0x124/0x130
[ 243.686908] [c000000016673e10] [c00000001000cd40] ret_from_kernel_thread+0x5c/0x64
[ 366.566274] INFO: task systemd:1 blocked for more than 245 seconds.
[ 366.566298] Not tainted 6.1.0-rc1 #1
[ 366.566305] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[ 366.566314] task:systemd state:D stack:0 pid:1 ppid:0 flags:0x00042000
[ 366.566329] Call Trace:
...
In that case, note that maxcpus=1 instead of nr_cpus=1 is used in the
kernel command line on the PowerPC platform. Consequently, the crash cpu
is the only onlined cpu in the kdump kernel, but with its logical id not
necessary 0. While SRCU queues a sdp->work on cpu 0, on which no worker
thread is created, so sdp->work will be never executed and
__synchronize_srcu() can not be completed.
Tackle this issue by replacing the cpu logic id 0 with
get_boot_cpu_id(). Since get_boot_cpu_id() guarantees the cpu to be once
online, based on the fact experienced by the running code.
Signed-off-by: Pingfan Liu <kernelfans@xxxxxxxxx>
Cc: "Paul E. McKenney" <paulmck@xxxxxxxxxx>
Cc: Lai Jiangshan <jiangshanlai@xxxxxxxxx>
Cc: Josh Triplett <josh@xxxxxxxxxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
To: rcu@xxxxxxxxxxxxxxx
---
kernel/rcu/srcutree.c | 9 +++++----
1 file changed, 5 insertions(+), 4 deletions(-)
diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
index 1c304fec89c0..4db36d543be3 100644
--- a/kernel/rcu/srcutree.c
+++ b/kernel/rcu/srcutree.c
@@ -663,7 +663,7 @@ static void srcu_gp_start(struct srcu_struct *ssp)
int state;
if (smp_load_acquire(&ssp->srcu_size_state) < SRCU_SIZE_WAIT_BARRIER)
- sdp = per_cpu_ptr(ssp->sda, 0);
+ sdp = per_cpu_ptr(ssp->sda, get_boot_cpu_id());
else
sdp = this_cpu_ptr(ssp->sda);
lockdep_assert_held(&ACCESS_PRIVATE(ssp, lock));
@@ -774,7 +774,8 @@ static void srcu_gp_end(struct srcu_struct *ssp)
/* Initiate callback invocation as needed. */
ss_state = smp_load_acquire(&ssp->srcu_size_state);
if (ss_state < SRCU_SIZE_WAIT_BARRIER) {
- srcu_schedule_cbs_sdp(per_cpu_ptr(ssp->sda, 0), cbdelay);
+ srcu_schedule_cbs_sdp(per_cpu_ptr(ssp->sda, get_boot_cpu_id()),
+ cbdelay);
} else {
idx = rcu_seq_ctr(gpseq) % ARRAY_SIZE(snp->srcu_have_cbs);
srcu_for_each_node_breadth_first(ssp, snp) {
@@ -1093,7 +1094,7 @@ static unsigned long srcu_gp_start_if_needed(struct srcu_struct *ssp,
idx = srcu_read_lock(ssp);
ss_state = smp_load_acquire(&ssp->srcu_size_state);
if (ss_state < SRCU_SIZE_WAIT_CALL)
- sdp = per_cpu_ptr(ssp->sda, 0);
+ sdp = per_cpu_ptr(ssp->sda, get_boot_cpu_id());
else
sdp = raw_cpu_ptr(ssp->sda);
spin_lock_irqsave_sdp_contention(sdp, &flags);
@@ -1429,7 +1430,7 @@ void srcu_barrier(struct srcu_struct *ssp)
idx = srcu_read_lock(ssp);
if (smp_load_acquire(&ssp->srcu_size_state) < SRCU_SIZE_WAIT_BARRIER)
- srcu_barrier_one_cpu(ssp, per_cpu_ptr(ssp->sda, 0));
+ srcu_barrier_one_cpu(ssp, per_cpu_ptr(ssp->sda, get_boot_cpu_id()));
else
for_each_possible_cpu(cpu)
srcu_barrier_one_cpu(ssp, per_cpu_ptr(ssp->sda, cpu));
--
2.31.1
