It was found that the following lockdep splat happened when the control
files of the debug controller are being read.
[ 1732.553607] =====================================================
[ 1732.560413] WARNING: SOFTIRQ-safe -> SOFTIRQ-unsafe lock order detected
[ 1732.567801] 4.18.0-345.el8.x86_64+debug #1 Not tainted
[ 1732.573536] -----------------------------------------------------
[ 1732.580344] read_all/7798 [HC0[0]:SC0[0]:HE0:SE1] is trying to acquire:
[ 1732.587729] ffffffffa8844630 (&selinux_ss.policy_rwlock){.+.?}-{2:2}, at: security_compute_av+0x6c/0xfe0
[ 1732.598335]
and this task is already holding:
[ 1732.604848] ffffffffa5d9c878 (css_set_lock){..-.}-{2:2}, at: current_css_set_read+0x84/0x540
[ 1732.614283] which would create a new lock dependency:
[ 1732.619922] (css_set_lock){..-.}-{2:2} -> (&selinux_ss.policy_rwlock){.+.?}-{2:2}
[ 1732.628383]
but this new dependency connects a SOFTIRQ-irq-safe lock:
[ 1732.637221] (css_set_lock){..-.}-{2:2}
[ 1732.637226]
... which became SOFTIRQ-irq-safe at:
[ 1732.648416] lock_acquire+0x1b1/0x890
[ 1732.652607] _raw_spin_lock_irqsave+0x4c/0x8c
[ 1732.657573] cgroup_free+0x74/0x140
[ 1732.661573] __put_task_struct+0xb4/0x2e0
[ 1732.666151] rcu_do_batch+0x3d4/0xba0
[ 1732.670338] rcu_core+0x5ab/0x8e0
[ 1732.674138] __do_softirq+0x1cb/0xa4f
[ 1732.678325] run_ksoftirqd+0x3a/0x70
[ 1732.682419] smpboot_thread_fn+0x30f/0x770
[ 1732.687094] kthread+0x344/0x410
[ 1732.690797] ret_from_fork+0x3a/0x50
[ 1732.694885]
to a SOFTIRQ-irq-unsafe lock:
[ 1732.701007] (&selinux_ss.policy_rwlock){.+.?}-{2:2}
[ 1732.701011]
... which became SOFTIRQ-irq-unsafe at:
[ 1732.713641] ...
[ 1732.713647] lock_acquire+0x1b1/0x890
[ 1732.719784] _raw_read_lock+0x3c/0x90
[ 1732.723970] security_compute_av+0x6c/0xfe0
[ 1732.728739] avc_compute_av+0xd3/0x620
[ 1732.733021] avc_has_perm+0x330/0x4b0
[ 1732.737201] security_task_alloc+0x8d/0x140
[ 1732.741971] copy_process+0x1d6d/0x6410
[ 1732.746353] _do_fork+0x107/0xbc0
[ 1732.750152] kernel_thread+0x25/0x30
[ 1732.754243] rest_init+0x26/0x200
[ 1732.758045] start_kernel+0x77c/0x7ba
[ 1732.762236] secondary_startup_64_no_verify+0xc2/0xcb
[ 1732.767971]
other info that might help us debug this:
[ 1732.776898] Possible interrupt unsafe locking scenario:
[ 1732.784469] CPU0 CPU1
[ 1732.789517] ---- ----
[ 1732.794565] lock(&selinux_ss.policy_rwlock);
[ 1732.799528] local_irq_disable();
[ 1732.806137] lock(css_set_lock);
[ 1732.812648] lock(&selinux_ss.policy_rwlock);
[ 1732.820413] <Interrupt>
[ 1732.823335] lock(css_set_lock);
[ 1732.827222]
*** DEADLOCK ***
[ 1732.833831] 6 locks held by read_all/7798:
[ 1732.838393] #0: ffff88811b46daf0 (&p->lock){+.+.}-{3:3}, at: seq_read+0x6b/0x1020
[ 1732.846857] #1: ffff888132826490 (&of->mutex){+.+.}-{3:3}, at: kernfs_seq_start+0x49/0x170
[ 1732.856192] #2: ffffffffa5d9c950 (cgroup_mutex){+.+.}-{3:3}, at: cgroup_kn_lock_live+0x14a/0x430
[ 1732.866105] #3: ffffffffa5d9c878 (css_set_lock){..-.}-{2:2}, at: current_css_set_read+0x84/0x540
[ 1732.876020] #4: ffffffffa5c819a0 (rcu_read_lock){....}-{1:2}, at: current_css_set_read+0x78/0x540
[ 1732.886032] #5: ffffffffa5c819a0 (rcu_read_lock){....}-{1:2}, at: has_ns_capability_noaudit+0x5/0x1c0
[ 1732.896435]
the dependencies between SOFTIRQ-irq-safe lock and the holding lock:
[ 1732.906361] -> (css_set_lock){..-.}-{2:2} {
[ 1732.911037] IN-SOFTIRQ-W at:
[ 1732.914548] lock_acquire+0x1b1/0x890
[ 1732.920482] _raw_spin_lock_irqsave+0x4c/0x8c
[ 1732.927190] cgroup_free+0x74/0x140
[ 1732.932929] __put_task_struct+0xb4/0x2e0
[ 1732.939250] rcu_do_batch+0x3d4/0xba0
[ 1732.945184] rcu_core+0x5ab/0x8e0
[ 1732.950727] __do_softirq+0x1cb/0xa4f
[ 1732.956660] run_ksoftirqd+0x3a/0x70
[ 1732.962495] smpboot_thread_fn+0x30f/0x770
[ 1732.968912] kthread+0x344/0x410
[ 1732.974359] ret_from_fork+0x3a/0x50
[ 1732.980191] INITIAL USE at:
[ 1732.983605] lock_acquire+0x1b1/0x890
[ 1732.989439] _raw_spin_lock_irq+0x46/0x90
[ 1732.995663] cgroup_setup_root+0x49d/0x920
[ 1733.001984] cgroup_init+0x20e/0xbb7
[ 1733.007721] start_kernel+0x754/0x7ba
[ 1733.013555] secondary_startup_64_no_verify+0xc2/0xcb
[ 1733.020939] }
[ 1733.022803] ... key at: [<ffffffffa5d9c878>] css_set_lock+0x18/0x80
[ 1733.030382] ... acquired at:
[ 1733.033696] __lock_acquire+0x21d1/0x2c60
[ 1733.038369] lock_acquire+0x1b1/0x890
[ 1733.042651] _raw_read_lock+0x3c/0x90
[ 1733.046934] security_compute_av+0x6c/0xfe0
[ 1733.051798] avc_compute_av+0xd3/0x620
[ 1733.056170] avc_has_perm_noaudit+0x2eb/0x490
[ 1733.061230] cred_has_capability+0x139/0x260
[ 1733.066193] security_capable+0x58/0x90
[ 1733.070670] has_ns_capability_noaudit+0xc7/0x1c0
[ 1733.076120] restricted_pointer+0x18a/0x410
[ 1733.080984] pointer+0x1de/0x700
[ 1733.084783] vsnprintf+0x7bd/0x1250
[ 1733.088873] seq_vprintf+0xbd/0x1a0
[ 1733.092963] seq_printf+0x9b/0xd0
[ 1733.096859] current_css_set_read+0x179/0x540
[ 1733.101918] seq_read+0x408/0x1020
[ 1733.105916] vfs_read+0xff/0x300
[ 1733.109715] ksys_read+0xb8/0x170
[ 1733.113614] do_syscall_64+0xa5/0x430
[ 1733.117899] entry_SYSCALL_64_after_hwframe+0x6a/0xdf
[ 1733.125392]
the dependencies between the lock to be acquired
[ 1733.125394] and SOFTIRQ-irq-unsafe lock:
[ 1733.137843] -> (&selinux_ss.policy_rwlock){.+.?}-{2:2} {
[ 1733.143779] HARDIRQ-ON-R at:
[ 1733.147289] lock_acquire+0x1b1/0x890
[ 1733.153223] _raw_read_lock+0x3c/0x90
[ 1733.159156] security_compute_av+0x6c/0xfe0
[ 1733.165670] avc_compute_av+0xd3/0x620
[ 1733.171699] avc_has_perm+0x330/0x4b0
[ 1733.177632] security_task_alloc+0x8d/0x140
[ 1733.184148] copy_process+0x1d6d/0x6410
[ 1733.190274] _do_fork+0x107/0xbc0
[ 1733.195820] kernel_thread+0x25/0x30
[ 1733.201654] rest_init+0x26/0x200
[ 1733.207198] start_kernel+0x77c/0x7ba
[ 1733.213131] secondary_startup_64_no_verify+0xc2/0xcb
[ 1733.220613] IN-SOFTIRQ-R at:
[ 1733.224123] lock_acquire+0x1b1/0x890
[ 1733.230057] _raw_read_lock+0x3c/0x90
[ 1733.235991] security_netlbl_sid_to_secattr+0xc3/0x330
[ 1733.243572] selinux_netlbl_inet_conn_request+0xf4/0x210
[ 1733.251348] selinux_inet_conn_request+0x1ad/0x270
[ 1733.258539] security_inet_conn_request+0x4f/0x90
[ 1733.265635] tcp_v6_route_req+0x2db/0x510
[ 1733.271958] tcp_conn_request+0xb06/0x2e40
[ 1733.278375] tcp_rcv_state_process+0x9d2/0x4971
[ 1733.285278] tcp_v6_do_rcv+0x6f5/0x1220
[ 1733.291403] tcp_v6_rcv+0x2c9d/0x3290
[ 1733.297337] ip6_protocol_deliver_rcu+0x27b/0x1560
[ 1733.304530] ip6_input_finish+0x6c/0x110
[ 1733.310753] ip6_input+0xd5/0x310
[ 1733.316298] ipv6_rcv+0x11c6/0x2400
[ 1733.322038] __netif_receive_skb_core+0x194a/0x3330
[ 1733.329328] process_backlog+0x21e/0x6b0
[ 1733.335551] __napi_poll+0x9f/0x520
[ 1733.341288] net_rx_action+0x36e/0x980
[ 1733.347317] __do_softirq+0x1cb/0xa4f
[ 1733.353250] do_softirq_own_stack+0x2a/0x40
[ 1733.359763] do_softirq.part.9+0x9b/0xb0
[ 1733.365988] __local_bh_enable_ip+0xef/0x110
[ 1733.372599] ip6_finish_output2+0x984/0x2340
[ 1733.379207] ip6_output+0x205/0x730
[ 1733.384940] ip6_xmit+0xc3c/0x1f60
[ 1733.390579] inet6_csk_xmit+0x2d0/0x4d3
[ 1733.396703] __tcp_transmit_skb+0x1704/0x38e0
[ 1733.403408] tcp_connect+0x28c5/0x3c80
[ 1733.409433] tcp_v6_connect+0x15ff/0x1f40
[ 1733.415752] __inet_stream_connect+0x64a/0xbf0
[ 1733.422554] inet_stream_connect+0x53/0xa0
[ 1733.428972] __sys_connect+0xfe/0x130
[ 1733.434900] __x64_sys_connect+0x6f/0xb0
[ 1733.441120] do_syscall_64+0xa5/0x430
[ 1733.447049] entry_SYSCALL_64_after_hwframe+0x6a/0xdf
[ 1733.454529] SOFTIRQ-ON-R at:
[ 1733.458034] lock_acquire+0x1b1/0x890
[ 1733.463962] _raw_read_lock+0x3c/0x90
[ 1733.469890] security_compute_av+0x6c/0xfe0
[ 1733.476401] avc_compute_av+0xd3/0x620
[ 1733.482425] avc_has_perm+0x330/0x4b0
[ 1733.488353] security_task_alloc+0x8d/0x140
[ 1733.494865] copy_process+0x1d6d/0x6410
[ 1733.500987] _do_fork+0x107/0xbc0
[ 1733.506527] kernel_thread+0x25/0x30
[ 1733.512358] rest_init+0x26/0x200
[ 1733.517898] start_kernel+0x77c/0x7ba
[ 1733.523826] secondary_startup_64_no_verify+0xc2/0xcb
[ 1733.531305] INITIAL READ USE at:
[ 1733.535199] lock_acquire+0x1b1/0x890
[ 1733.541516] _raw_read_lock+0x3c/0x90
[ 1733.547833] security_compute_av+0x6c/0xfe0
[ 1733.554731] avc_compute_av+0xd3/0x620
[ 1733.561144] avc_has_perm+0x330/0x4b0
[ 1733.567461] security_task_alloc+0x8d/0x140
[ 1733.574360] copy_process+0x1d6d/0x6410
[ 1733.580863] _do_fork+0x107/0xbc0
[ 1733.586784] kernel_thread+0x25/0x30
[ 1733.593003] rest_init+0x26/0x200
[ 1733.598931] start_kernel+0x77c/0x7ba
[ 1733.605247] secondary_startup_64_no_verify+0xc2/0xcb
[ 1733.613113] }
[ 1733.614971] ... key at: [<ffffffffa8844380>] __key.89897+0x0/0x40
[ 1733.622354] ... acquired at:
[ 1733.625664] __lock_acquire+0x21d1/0x2c60
[ 1733.630333] lock_acquire+0x1b1/0x890
[ 1733.634613] _raw_read_lock+0x3c/0x90
[ 1733.638894] security_compute_av+0x6c/0xfe0
[ 1733.643756] avc_compute_av+0xd3/0x620
[ 1733.648133] avc_has_perm_noaudit+0x2eb/0x490
[ 1733.653190] cred_has_capability+0x139/0x260
[ 1733.658139] security_capable+0x58/0x90
[ 1733.662614] has_ns_capability_noaudit+0xc7/0x1c0
[ 1733.668059] restricted_pointer+0x18a/0x410
[ 1733.672911] pointer+0x1de/0x700
[ 1733.676706] vsnprintf+0x7bd/0x1250
[ 1733.680792] seq_vprintf+0xbd/0x1a0
[ 1733.684878] seq_printf+0x9b/0xd0
[ 1733.688771] current_css_set_read+0x179/0x540
[ 1733.693828] seq_read+0x408/0x1020
[ 1733.697817] vfs_read+0xff/0x300
[ 1733.701612] ksys_read+0xb8/0x170
[ 1733.705504] do_syscall_64+0xa5/0x430
[ 1733.709785] entry_SYSCALL_64_after_hwframe+0x6a/0xdf
[ 1733.717274]
stack backtrace:
[ 1733.722140] CPU: 4 PID: 7798 Comm: read_all Kdump: loaded Not tainted 4.18.0-345.el8.x86_64+debug #1
[ 1733.732333] Hardware name: Dell Inc. PowerEdge R720/0X6FFV, BIOS 2.1.2 09/19/2013
[ 1733.740686] Call Trace:
[ 1733.743423] dump_stack+0x8e/0xd0
[ 1733.747124] check_irq_usage.cold.57+0x566/0x7b6
[ 1733.805114] check_prevs_add+0x409/0x21d0
[ 1733.835277] __lock_acquire+0x21d1/0x2c60
[ 1733.839761] lock_acquire+0x1b1/0x890
[ 1733.865825] _raw_read_lock+0x3c/0x90
[ 1733.874779] security_compute_av+0x6c/0xfe0
[ 1733.888306] avc_compute_av+0xd3/0x620
[ 1733.892494] avc_has_perm_noaudit+0x2eb/0x490
[ 1733.907384] cred_has_capability+0x139/0x260
[ 1733.926460] security_capable+0x58/0x90
[ 1733.930743] has_ns_capability_noaudit+0xc7/0x1c0
[ 1733.935997] restricted_pointer+0x18a/0x410
[ 1733.950203] pointer+0x1de/0x700
[ 1733.966360] vsnprintf+0x7bd/0x1250
[ 1733.979006] seq_vprintf+0xbd/0x1a0
[ 1733.982901] seq_printf+0x9b/0xd0
[ 1733.990790] current_css_set_read+0x179/0x540
[ 1733.995657] seq_read+0x408/0x1020
[ 1733.999461] vfs_read+0xff/0x300
[ 1734.003065] ksys_read+0xb8/0x170
[ 1734.021070] do_syscall_64+0xa5/0x430
[ 1734.025159] entry_SYSCALL_64_after_hwframe+0x6a/0xdf
The lockdep splat is caused by the fact that the debug controller use the
"%pK" format specifier to print out address of cset's with css_set_lock
held. Under some circumstances, the use of "%pK" format specifier may
acquire the selinux_ss.policy_rwlock.
To avoid this possible deadlock scenario, we have to abandon the use of
the "%pK" format specifier and just use "%p" to always hash the cset
addresses. The actual cset addresses aren't that important as long as
they are unique for matching purpose.
Signed-off-by: Waiman Long <longman@xxxxxxxxxx>
---
kernel/cgroup/debug.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/kernel/cgroup/debug.c b/kernel/cgroup/debug.c
index 80aa3f027ac3..fbf7bdbae1a2 100644
--- a/kernel/cgroup/debug.c
+++ b/kernel/cgroup/debug.c
@@ -52,7 +52,7 @@ static int current_css_set_read(struct seq_file *seq, void *v)
rcu_read_lock();
cset = task_css_set(current);
refcnt = refcount_read(&cset->refcount);
- seq_printf(seq, "css_set %pK %d", cset, refcnt);
+ seq_printf(seq, "css_set %p %d", cset, refcnt);
if (refcnt > cset->nr_tasks)
seq_printf(seq, " +%d", refcnt - cset->nr_tasks);
seq_puts(seq, "\n");
@@ -129,10 +129,10 @@ static int cgroup_css_links_read(struct seq_file *seq, void *v)
* Print out the proc_cset and threaded_cset relationship
* and highlight difference between refcount and task_count.
*/
- seq_printf(seq, "css_set %pK", cset);
+ seq_printf(seq, "css_set %p", cset);
if (rcu_dereference_protected(cset->dom_cset, 1) != cset) {
threaded_csets++;
- seq_printf(seq, "=>%pK", cset->dom_cset);
+ seq_printf(seq, "=>%p", cset->dom_cset);
}
if (!list_empty(&cset->threaded_csets)) {
struct css_set *tcset;
@@ -141,7 +141,7 @@ static int cgroup_css_links_read(struct seq_file *seq, void *v)
list_for_each_entry(tcset, &cset->threaded_csets,
threaded_csets_node) {
seq_puts(seq, idx ? "," : "<=");
- seq_printf(seq, "%pK", tcset);
+ seq_printf(seq, "%p", tcset);
idx++;
}
} else {
--
2.18.1
