Re: [PATCH v8 -tip 20/26] sched: Release references to the per-task cookie on exit

From: chris hyser
Date: Wed Nov 04 2020 - 16:54:08 EST

On 10/19/20 9:43 PM, Joel Fernandes (Google) wrote:
During exit, we have to free the references to a cookie that might be shared by
many tasks. This commit therefore ensures when the task_struct is released, any
references to cookies that it holds are also released.

Tested-by: Julien Desfossez <jdesfossez@xxxxxxxxxxxxxxxx>
Signed-off-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx>
---
include/linux/sched.h | 2 ++
kernel/fork.c | 1 +
kernel/sched/core.c | 8 ++++++++
3 files changed, 11 insertions(+)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 4cb76575afa8..eabd96beff92 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -2079,12 +2079,14 @@ void sched_core_unsafe_exit(void);
bool sched_core_wait_till_safe(unsigned long ti_check);
bool sched_core_kernel_protected(void);
int sched_core_share_pid(pid_t pid);
+void sched_tsk_free(struct task_struct *tsk);
#else
#define sched_core_unsafe_enter(ignore) do { } while (0)
#define sched_core_unsafe_exit(ignore) do { } while (0)
#define sched_core_wait_till_safe(ignore) do { } while (0)
#define sched_core_kernel_protected(ignore) do { } while (0)
#define sched_core_share_pid(pid_t pid) do { } while (0)
+#define sched_tsk_free(tsk) do { } while (0)
#endif
#endif
diff --git a/kernel/fork.c b/kernel/fork.c
index b9c289d0f4ef..a39248a02fdd 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -736,6 +736,7 @@ void __put_task_struct(struct task_struct *tsk)
exit_creds(tsk);
delayacct_tsk_free(tsk);
put_signal_struct(tsk->signal);
+ sched_tsk_free(tsk);
if (!profile_handoff_task(tsk))
free_task(tsk);
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 42aa811eab14..61e1dcf11000 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -9631,6 +9631,14 @@ static int cpu_core_tag_color_write_u64(struct cgroup_subsys_state *css,
return 0;
}
+
+void sched_tsk_free(struct task_struct *tsk)
+{
+ if (!tsk->core_task_cookie)
+ return;
+ sched_core_put_task_cookie(tsk->core_task_cookie);
+ sched_core_put();


sched_tsk_free() can be called under softirq. sched_core_put() is riddled with things that may want to sleep.

[root@chyser-vm6 bin]# [ 135.349453] BUG: sleeping function called from invalid context at kernel/locking/mutex.c:281
[ 135.356381] in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 0, name: swapper/1
[ 135.364331] CPU: 1 PID: 0 Comm: swapper/1 Tainted: G E 5.9.0_ch_pick_task_v8_fix_4+ #15
[ 135.370178] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 0.0.0 02/06/2015
[ 135.372052] Call Trace:
[ 135.372733] <IRQ>
[ 135.373162] dump_stack+0x74/0x92
[ 135.375134] ___might_sleep.cold+0x94/0xa5
[ 135.379102] __might_sleep+0x4b/0x80
[ 135.382509] mutex_lock+0x21/0x50
[ 135.385616] sched_core_put+0x15/0x70
[ 135.388981] sched_tsk_free+0x20/0x30
[ 135.389753] __put_task_struct+0xbe/0x190
[ 135.390896] delayed_put_task_struct+0x88/0xa0
[ 135.391812] rcu_core+0x341/0x520
[ 135.392580] rcu_core_si+0xe/0x10
[ 135.393281] __do_softirq+0xe8/0x2cd
[ 135.394030] asm_call_irq_on_stack+0x12/0x20
[ 135.395060] </IRQ>
[ 135.395519] do_softirq_own_stack+0x3d/0x50
[ 135.396379] irq_exit_rcu+0xb2/0xc0
[ 135.397203] sysvec_apic_timer_interrupt+0x3d/0x90
[ 135.398188] asm_sysvec_apic_timer_interrupt+0x12/0x20
[ 135.399395] RIP: 0010:native_safe_halt+0xe/0x10
[ 135.400314] Code: 7b ff ff ff eb bd cc cc cc cc cc cc e9 07 00 00 00 0f 00 2d 06 01 57 00 f4 c3 66 90 e9 07 00 00 00 0f 00 2d f6 00 57 00 fb f4 <c3> cc 0f 1f 44 00 00 55 48 89 e5 53 e8 b1 f2 63 ff 65 8b 15 5a 5d
[ 135.404484] RSP: 0018:ffffb41f4007be90 EFLAGS: 00000206
[ 135.405627] RAX: ffffffff9ea9b670 RBX: 0000000000000001 RCX: ffff9d3130d2ca80
[ 135.407201] RDX: 000000000001d576 RSI: ffffb41f4007be38 RDI: 0000001f839d2693
[ 135.409411] RBP: ffffb41f4007be98 R08: 0000000000000001 R09: 0000000000000000
[ 135.413731] R10: 0000000000000002 R11: ffff9d3130d2bd00 R12: ffff9d2e40853e80
[ 135.415161] R13: ffff9d2e40853e80 R14: 0000000000000000 R15: 0000000000000000
[ 135.416861] ? __sched_text_end+0x7/0x7
[ 135.417758] ? default_idle+0xe/0x20
[ 135.418505] arch_cpu_idle+0x15/0x20
[ 135.419225] default_idle_call+0x38/0xd0
[ 135.420145] do_idle+0x1ee/0x260
[ 135.421908] cpu_startup_entry+0x20/0x30
[ 135.425635] start_secondary+0x118/0x150
[ 135.429498] secondary_startup_64_no_verify+0xb8/0xbb

I tried a number of things like replacing the mutexes in put/get with spin_lock_bh() and just kept finding things like:


[root@chyser-vm5 bin]# [ 1123.516209] BUG: sleeping function called from invalid context at include/linux/percpu-rwsem.h:49
[ 1123.517976] in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 0, name: swapper/15
[ 1123.519557] CPU: 15 PID: 0 Comm: swapper/15 Tainted: G E 5.9.0_ch_pick_task_v8_fix_5+ #16
[ 1123.521392] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 0.0.0 02/06/2015
[ 1123.523039] Call Trace:
[ 1123.523546] <IRQ>
[ 1123.523961] dump_stack+0x74/0x92
[ 1123.524632] ___might_sleep.cold+0x94/0xa5
[ 1123.525442] __might_sleep+0x4b/0x80
[ 1123.526131] ? cpumask_weight+0x20/0x20
[ 1123.526896] cpus_read_lock+0x1c/0x60
[ 1123.527623] stop_machine+0x1d/0x40
[ 1123.528321] __sched_core_disable+0x19/0x40
[ 1123.529133] sched_core_put+0x18/0x20
[ 1123.529852] sched_tsk_free+0x20/0x30
[ 1123.530571] __put_task_struct+0xbe/0x190
[ 1123.531361] delayed_put_task_struct+0x88/0xa0
[ 1123.532234] rcu_core+0x341/0x520
[ 1123.532882] rcu_core_si+0xe/0x10
[ 1123.533554] __do_softirq+0xe8/0x2cd
[ 1123.534281] asm_call_irq_on_stack+0x12/0x20
[ 1123.535153] </IRQ>
[ 1123.535584] do_softirq_own_stack+0x3d/0x50
[ 1123.536403] irq_exit_rcu+0xb2/0xc0
[ 1123.537080] sysvec_apic_timer_interrupt+0x3d/0x90
[ 1123.538002] asm_sysvec_apic_timer_interrupt+0x12/0x20
[ 1123.539000] RIP: 0010:native_safe_halt+0xe/0x10
[ 1123.539886] Code: 7b ff ff ff eb bd cc cc cc cc cc cc e9 07 00 00 00 0f 00 2d d6 00 57 00 f4 c3 66 90 e9 07 00 00 00 0f 00 2d c6 00 57 00 fb f4 <c3> cc 0f 1f 44 00 00 55 48 89 e5 53 e8 91 f2 63 ff 65 8b 15 2a 5d
[ 1123.543776] RSP: 0018:ffffa830800ebe90 EFLAGS: 00000206
[ 1123.544915] RAX: ffffffffa7c9b6a0 RBX: 000000000000000f RCX: ffff99af07deca80
[ 1123.546556] RDX: 000000000048f6e6 RSI: ffffa830800ebe38 RDI: 0000010599561e7a
[ 1123.548091] RBP: ffffa830800ebe98 R08: 0000000000000001 R09: 000000000000000e
[ 1123.549453] R10: ffff9992422012c8 R11: ffff9992422012cc R12: ffff999240a59f40
[ 1123.550815] R13: ffff999240a59f40 R14: 0000000000000000 R15: 0000000000000000
[ 1123.552188] ? __sched_text_end+0x7/0x7
[ 1123.552939] ? default_idle+0xe/0x20
[ 1123.553635] arch_cpu_idle+0x15/0x20
[ 1123.554341] default_idle_call+0x38/0xd0
[ 1123.555111] do_idle+0x1ee/0x26



The prctl() parts of the selftests pass, but all the above is caused by simply calling prctl() to "share a cookie w/ a task" that then dies after second.

-chrish