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#syz test:
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[syzbot] [input?] WARNING in bcm5974_start_traffic/usb_submit_urb (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    fec50db7033e Linux 6.9-rc3
git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci
console output: https://syzkaller.appspot.com/x/log.txt?x=14439bd3180000
kernel config:  https://syzkaller.appspot.com/x/.config?x=560f5db1d0b3f6d0
dashboard link: https://syzkaller.appspot.com/bug?extid=b064b5599f18f7ebb1e1
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
userspace arch: arm64
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=11c2c5bd180000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=13cbbf5b180000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/ab4d6cae2eca/disk-fec50db7.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/b67542cc5860/vmlinux-fec50db7.xz
kernel image: https://storage.googleapis.com/syzbot-assets/3eeebb470b79/Image-fec50db7.gz.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+b064b5599f18f7ebb1e1@syzkaller.appspotmail.com

------------[ cut here ]------------
usb 1-1: BOGUS urb xfer, pipe 1 != type 3
WARNING: CPU: 0 PID: 6237 at drivers/usb/core/urb.c:504 usb_submit_urb+0xa00/0x1434 drivers/usb/core/urb.c:503
Modules linked in:
CPU: 0 PID: 6237 Comm: udevd Not tainted 6.9.0-rc3-syzkaller-gfec50db7033e #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/27/2024
pstate: 60400005 (nZCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
pc : usb_submit_urb+0xa00/0x1434 drivers/usb/core/urb.c:503
lr : usb_submit_urb+0xa00/0x1434 drivers/usb/core/urb.c:503
sp : ffff80009f8b73b0
x29: ffff80009f8b73f0 x28: ffff0000d4fee000 x27: 0000000000000001
x26: ffff80008c6919e8 x25: ffff0000c8bd1fe0 x24: ffff0000c1d45a50
x23: ffff80008c698500 x22: dfff800000000000 x21: 0000000000000002
x20: 0000000000000cc0 x19: ffff0000c1d45a00 x18: 0000000000000008
x17: 0000000000000000 x16: ffff80008ae6d1bc x15: 0000000000000001
x14: 1fffe000367b9a02 x13: 0000000000000000 x12: 0000000000000000
x11: 0000000000000002 x10: 0000000000ff0100 x9 : b1573c5f9bab7600
x8 : b1573c5f9bab7600 x7 : 0000000000000001 x6 : 0000000000000001
x5 : ffff80009f8b6b18 x4 : ffff80008ef65000 x3 : ffff8000805e9200
x2 : 0000000000000001 x1 : 0000000100000000 x0 : 0000000000000000
Call trace:
 usb_submit_urb+0xa00/0x1434 drivers/usb/core/urb.c:503
 bcm5974_start_traffic+0xe0/0x154 drivers/input/mouse/bcm5974.c:799
 bcm5974_open+0x98/0x134 drivers/input/mouse/bcm5974.c:839
 input_open_device+0x170/0x29c drivers/input/input.c:654
 evdev_open_device drivers/input/evdev.c:400 [inline]
 evdev_open+0x308/0x4b4 drivers/input/evdev.c:487
 chrdev_open+0x3c8/0x4dc fs/char_dev.c:414
 do_dentry_open+0x778/0x12b4 fs/open.c:955
 vfs_open+0x7c/0x90 fs/open.c:1089
 do_open fs/namei.c:3642 [inline]
 path_openat+0x1f6c/0x2830 fs/namei.c:3799
 do_filp_open+0x1bc/0x3cc fs/namei.c:3826
 do_sys_openat2+0x124/0x1b8 fs/open.c:1406
 do_sys_open fs/open.c:1421 [inline]
 __do_sys_openat fs/open.c:1437 [inline]
 __se_sys_openat fs/open.c:1432 [inline]
 __arm64_sys_openat+0x1f0/0x240 fs/open.c:1432
 __invoke_syscall arch/arm64/kernel/syscall.c:34 [inline]
 invoke_syscall+0x98/0x2b8 arch/arm64/kernel/syscall.c:48
 el0_svc_common+0x130/0x23c arch/arm64/kernel/syscall.c:133
 do_el0_svc+0x48/0x58 arch/arm64/kernel/syscall.c:152
 el0_svc+0x54/0x168 arch/arm64/kernel/entry-common.c:712
 el0t_64_sync_handler+0x84/0xfc arch/arm64/kernel/entry-common.c:730
 el0t_64_sync+0x190/0x194 arch/arm64/kernel/entry.S:598
irq event stamp: 5626
hardirqs last  enabled at (5625): [<ffff8000803749b0>] __up_console_sem kernel/printk/printk.c:341 [inline]
hardirqs last  enabled at (5625): [<ffff8000803749b0>] __console_unlock kernel/printk/printk.c:2731 [inline]
hardirqs last  enabled at (5625): [<ffff8000803749b0>] console_unlock+0x17c/0x3d4 kernel/printk/printk.c:3050
hardirqs last disabled at (5626): [<ffff80008ae68608>] el1_dbg+0x24/0x80 arch/arm64/kernel/entry-common.c:470
softirqs last  enabled at (2362): [<ffff800080031848>] local_bh_enable+0x10/0x34 include/linux/bottom_half.h:32
softirqs last disabled at (2360): [<ffff800080031814>] local_bh_disable+0x10/0x34 include/linux/bottom_half.h:19
---[ end trace 0000000000000000 ]---


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzkaller@googlegroups.com.

syzbot will keep track of this issue. See:
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If the report is already addressed, let syzbot know by replying with:
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If you want syzbot to run the reproducer, reply with:
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Re: [syzbot] Test

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Subject: Test
Author: mukattreyee@gmail.com

#syz test:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master

Re: [syzbot] [input?] WARNING in bcm5974_start_traffic/usb_submit_urb (2)

[Javier Carrasco]

On 4/15/24 03:54, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    fec50db7033e Linux 6.9-rc3
> git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci
> console output: https://syzkaller.appspot.com/x/log.txt?x=14439bd3180000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=560f5db1d0b3f6d0
> dashboard link: https://syzkaller.appspot.com/bug?extid=b064b5599f18f7ebb1e1
> compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
> userspace arch: arm64
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=11c2c5bd180000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=13cbbf5b180000
> 
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/ab4d6cae2eca/disk-fec50db7.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/b67542cc5860/vmlinux-fec50db7.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/3eeebb470b79/Image-fec50db7.gz.xz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+b064b5599f18f7ebb1e1@syzkaller.appspotmail.com
> 
> ------------[ cut here ]------------
> usb 1-1: BOGUS urb xfer, pipe 1 != type 3
> WARNING: CPU: 0 PID: 6237 at drivers/usb/core/urb.c:504 usb_submit_urb+0xa00/0x1434 drivers/usb/core/urb.c:503
> Modules linked in:
> CPU: 0 PID: 6237 Comm: udevd Not tainted 6.9.0-rc3-syzkaller-gfec50db7033e #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/27/2024
> pstate: 60400005 (nZCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
> pc : usb_submit_urb+0xa00/0x1434 drivers/usb/core/urb.c:503
> lr : usb_submit_urb+0xa00/0x1434 drivers/usb/core/urb.c:503
> sp : ffff80009f8b73b0
> x29: ffff80009f8b73f0 x28: ffff0000d4fee000 x27: 0000000000000001
> x26: ffff80008c6919e8 x25: ffff0000c8bd1fe0 x24: ffff0000c1d45a50
> x23: ffff80008c698500 x22: dfff800000000000 x21: 0000000000000002
> x20: 0000000000000cc0 x19: ffff0000c1d45a00 x18: 0000000000000008
> x17: 0000000000000000 x16: ffff80008ae6d1bc x15: 0000000000000001
> x14: 1fffe000367b9a02 x13: 0000000000000000 x12: 0000000000000000
> x11: 0000000000000002 x10: 0000000000ff0100 x9 : b1573c5f9bab7600
> x8 : b1573c5f9bab7600 x7 : 0000000000000001 x6 : 0000000000000001
> x5 : ffff80009f8b6b18 x4 : ffff80008ef65000 x3 : ffff8000805e9200
> x2 : 0000000000000001 x1 : 0000000100000000 x0 : 0000000000000000
> Call trace:
>  usb_submit_urb+0xa00/0x1434 drivers/usb/core/urb.c:503
>  bcm5974_start_traffic+0xe0/0x154 drivers/input/mouse/bcm5974.c:799
>  bcm5974_open+0x98/0x134 drivers/input/mouse/bcm5974.c:839
>  input_open_device+0x170/0x29c drivers/input/input.c:654
>  evdev_open_device drivers/input/evdev.c:400 [inline]
>  evdev_open+0x308/0x4b4 drivers/input/evdev.c:487
>  chrdev_open+0x3c8/0x4dc fs/char_dev.c:414
>  do_dentry_open+0x778/0x12b4 fs/open.c:955
>  vfs_open+0x7c/0x90 fs/open.c:1089
>  do_open fs/namei.c:3642 [inline]
>  path_openat+0x1f6c/0x2830 fs/namei.c:3799
>  do_filp_open+0x1bc/0x3cc fs/namei.c:3826
>  do_sys_openat2+0x124/0x1b8 fs/open.c:1406
>  do_sys_open fs/open.c:1421 [inline]
>  __do_sys_openat fs/open.c:1437 [inline]
>  __se_sys_openat fs/open.c:1432 [inline]
>  __arm64_sys_openat+0x1f0/0x240 fs/open.c:1432
>  __invoke_syscall arch/arm64/kernel/syscall.c:34 [inline]
>  invoke_syscall+0x98/0x2b8 arch/arm64/kernel/syscall.c:48
>  el0_svc_common+0x130/0x23c arch/arm64/kernel/syscall.c:133
>  do_el0_svc+0x48/0x58 arch/arm64/kernel/syscall.c:152
>  el0_svc+0x54/0x168 arch/arm64/kernel/entry-common.c:712
>  el0t_64_sync_handler+0x84/0xfc arch/arm64/kernel/entry-common.c:730
>  el0t_64_sync+0x190/0x194 arch/arm64/kernel/entry.S:598
> irq event stamp: 5626
> hardirqs last  enabled at (5625): [<ffff8000803749b0>] __up_console_sem kernel/printk/printk.c:341 [inline]
> hardirqs last  enabled at (5625): [<ffff8000803749b0>] __console_unlock kernel/printk/printk.c:2731 [inline]
> hardirqs last  enabled at (5625): [<ffff8000803749b0>] console_unlock+0x17c/0x3d4 kernel/printk/printk.c:3050
> hardirqs last disabled at (5626): [<ffff80008ae68608>] el1_dbg+0x24/0x80 arch/arm64/kernel/entry-common.c:470
> softirqs last  enabled at (2362): [<ffff800080031848>] local_bh_enable+0x10/0x34 include/linux/bottom_half.h:32
> softirqs last disabled at (2360): [<ffff800080031814>] local_bh_disable+0x10/0x34 include/linux/bottom_half.h:19
> ---[ end trace 0000000000000000 ]---
> 
> 
> ---
> This report is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
> syzbot engineers can be reached at syzkaller@googlegroups.com.
> 
> syzbot will keep track of this issue. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
> 
> If the report is already addressed, let syzbot know by replying with:
> #syz fix: exact-commit-title
> 
> If you want syzbot to run the reproducer, reply with:
> #syz test: git://repo/address.git branch-or-commit-hash
> If you attach or paste a git patch, syzbot will apply it before testing.
> 
> If you want to overwrite report's subsystems, reply with:
> #syz set subsystems: new-subsystem
> (See the list of subsystem names on the web dashboard)
> 
> If the report is a duplicate of another one, reply with:
> #syz dup: exact-subject-of-another-report
> 
> If you want to undo deduplication, reply with:
> #syz undup
> 

This is a known bug in the bcm5974 driver that was fixed with commit
2b9c3eb32a69 ("Input: bcm5974 - check endpoint type before starting
traffic").

The fix had to be reverted due to a more severe bug that was hidden by
this one and caused a regression: the driver makes use of endpoints that
belong to interfaces it did not bind to (see discussion here [1]). In a
nutshell, any check to make sure that the endpoint belongs to a bound
interface will fail.

In order to apply the fix for the bug syzbot found again, the
inteface/endpoint issue must be solved first, making sure that the
driver binds to the right interfaces.

Link: https://lore.kernel.org/87sf161jjc.wl-tiwai@suse.de/ [1]

Best regards,
Javier Carrasco

Re: [syzbot] test

[syzbot]

For archival purposes, forwarding an incoming command email to
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Subject: test
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#syz test:
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Re: [syzbot] test

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#syz test:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master

Re: [syzbot] Test

[syzbot]

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Subject: Test
Author: radoslaw.zielonek@gmail.com

#syz test https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git 71b1543c83d65af8215d7558d70fc2ecbee77dcf

---
 net/sched/sch_taprio.c | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/net/sched/sch_taprio.c b/net/sched/sch_taprio.c
index a0d54b422186..41add4a1d407 100644
--- a/net/sched/sch_taprio.c
+++ b/net/sched/sch_taprio.c
@@ -44,6 +44,8 @@ static struct static_key_false taprio_have_working_mqprio;
 	(TCA_TAPRIO_ATTR_FLAG_TXTIME_ASSIST | TCA_TAPRIO_ATTR_FLAG_FULL_OFFLOAD)
 #define TAPRIO_FLAGS_INVALID U32_MAX
 
+#define TAPRIO_MAX_NUM_SCHEDULES_BEFORE_NOW 10
+
 struct sched_entry {
 	/* Durations between this GCL entry and the GCL entry where the
 	 * respective traffic class gate closes
@@ -62,6 +64,8 @@ struct sched_entry {
 	u32 gate_mask;
 	u32 interval;
 	u8 command;
+	/* Used to skip some cycles to prevent other tasks from starving */
+	u8 num_schedules_before_now;
 };
 
 struct sched_gate_list {
@@ -111,6 +115,9 @@ struct __tc_taprio_qopt_offload {
 	struct tc_taprio_qopt_offload offload;
 };
 
+static void setup_txtime(struct taprio_sched *q,
+			 struct sched_gate_list *sched, ktime_t base);
+
 static void taprio_calculate_gate_durations(struct taprio_sched *q,
 					    struct sched_gate_list *sched)
 {
@@ -919,6 +926,7 @@ static enum hrtimer_restart advance_sched(struct hrtimer *timer)
 	struct sched_entry *entry, *next;
 	struct Qdisc *sch = q->root;
 	ktime_t end_time;
+	ktime_t basenow;
 	int tc;
 
 	spin_lock(&q->current_entry_lock);
@@ -977,6 +985,23 @@ static enum hrtimer_restart advance_sched(struct hrtimer *timer)
 	taprio_set_budgets(q, oper, next);
 
 first_run:
+	basenow = ktime_get();
+	if (ktime_before(end_time, basenow))
+	{
+		next->num_schedules_before_now++;
+		if (next->num_schedules_before_now >= TAPRIO_MAX_NUM_SCHEDULES_BEFORE_NOW)
+		{
+			end_time = ktime_add_ns(basenow, oper->cycle_time);
+			next->end_time = end_time;
+			next->num_schedules_before_now = 0;
+			setup_txtime(q, oper, basenow);
+		}
+	}
+	else
+	{
+		next->num_schedules_before_now = 0;
+	}
+
 	rcu_assign_pointer(q->current_entry, next);
 	spin_unlock(&q->current_entry_lock);
 
@@ -1074,6 +1099,7 @@ static int parse_sched_entry(struct taprio_sched *q, struct nlattr *n,
 	}
 
 	entry->index = index;
+	entry->num_schedules_before_now = 0;
 
 	return fill_sched_entry(q, tb, entry, extack);
 }
-- 
2.43.0

Re: [syzbot] test

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Subject: test
Author: mukattreyee@gmail.com

#syz test:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master

Re: [syzbot] Test

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Subject: Test
Author: radoslaw.zielonek@gmail.com

#syz test https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git fe46a7dd189e25604716c03576d05ac8a5209743

---
 include/linux/sched.h |  7 +++++++
 kernel/sched/core.c   |  1 +
 kernel/sched/rt.c     | 26 +++++++++++++++++++++++---
 kernel/signal.c       |  9 +++++++++
 4 files changed, 40 insertions(+), 3 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 17cb0761ff65..123bc16ad3d0 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1121,6 +1121,13 @@ struct task_struct {
 	size_t				sas_ss_size;
 	unsigned int			sas_ss_flags;
 
+	/*
+	 * Number of signals received by an RT task between scheduling ticks.
+	 * This counter is used to throttle RT tasks when too many signals
+	 * (e.g., POSIX timers) are sent to the task, which can cause an RCU stall.
+	 */
+	atomic_t rt_signals_recv_count; /* used outside of the rq lock */
+
 	struct callback_head		*task_works;
 
 #ifdef CONFIG_AUDIT
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index d44efa0d0611..9def826bd35f 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4779,6 +4779,7 @@ int sched_fork(unsigned long clone_flags, struct task_struct *p)
 			p->policy = SCHED_NORMAL;
 			p->static_prio = NICE_TO_PRIO(0);
 			p->rt_priority = 0;
+			atomic_set(&p->rt_signals_recv_count, 0);
 		} else if (PRIO_TO_NICE(p->static_prio) < 0)
 			p->static_prio = NICE_TO_PRIO(0);
 
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 3261b067b67e..9b22d67d1746 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -24,6 +24,15 @@ int sysctl_sched_rt_period = 1000000;
  */
 int sysctl_sched_rt_runtime = 950000;
 
+/*
+ * To avoid an RCU stall due to a large number of signals received by RT tasks
+ * (e.g., POSIX timers), the RT task needs to be throttled.
+ * When the number of signals received by an RT task during a scheduling
+ * tick period exceeds the threshold, the RT task will be throttled.
+ * The value of 100 has not been thoroughly tested and may need adjustment.
+ */
+#define RT_RECV_SGINAL_THROTTLE_THRESHOLD 100
+
 #ifdef CONFIG_SYSCTL
 static int sysctl_sched_rr_timeslice = (MSEC_PER_SEC * RR_TIMESLICE) / HZ;
 static int sched_rt_handler(struct ctl_table *table, int write, void *buffer,
@@ -951,7 +960,7 @@ static inline int rt_se_prio(struct sched_rt_entity *rt_se)
 	return rt_task_of(rt_se)->prio;
 }
 
-static int sched_rt_runtime_exceeded(struct rt_rq *rt_rq)
+static int sched_rt_runtime_exceeded(struct rt_rq *rt_rq, int rt_signal_recv)
 {
 	u64 runtime = sched_rt_runtime(rt_rq);
 
@@ -966,7 +975,15 @@ static int sched_rt_runtime_exceeded(struct rt_rq *rt_rq)
 	if (runtime == RUNTIME_INF)
 		return 0;
 
-	if (rt_rq->rt_time > runtime) {
+	/*
+	 * When a large number of signals are sent to this task (e.g., POSIX timers)
+	 * the delta time deviates significantly from real time due to the overhead
+	 * of handling signals. For RT tasks, this can cause an RCU stall.
+	 * To avoid this, throttle the task when the number of signals received
+	 * exceeds a certain threshold.
+	 */
+	if (rt_rq->rt_time > runtime ||
+		rt_signal_recv >= RT_RECV_SGINAL_THROTTLE_THRESHOLD) {
 		struct rt_bandwidth *rt_b = sched_rt_bandwidth(rt_rq);
 
 		/*
@@ -1021,7 +1038,9 @@ static void update_curr_rt(struct rq *rq)
 		if (sched_rt_runtime(rt_rq) != RUNTIME_INF) {
 			raw_spin_lock(&rt_rq->rt_runtime_lock);
 			rt_rq->rt_time += delta_exec;
-			exceeded = sched_rt_runtime_exceeded(rt_rq);
+			exceeded = sched_rt_runtime_exceeded(
+						rt_rq,
+						atomic_read(&curr->rt_signals_recv_count));
 			if (exceeded)
 				resched_curr(rq);
 			raw_spin_unlock(&rt_rq->rt_runtime_lock);
@@ -1029,6 +1048,7 @@ static void update_curr_rt(struct rq *rq)
 				do_start_rt_bandwidth(sched_rt_bandwidth(rt_rq));
 		}
 	}
+	atomic_set(&curr->rt_signals_recv_count, 0);
 }
 
 static void
diff --git a/kernel/signal.c b/kernel/signal.c
index bdca529f0f7b..d58e0ba9336c 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -629,6 +629,15 @@ int dequeue_signal(struct task_struct *tsk, sigset_t *mask,
 	bool resched_timer = false;
 	int signr;
 
+	/*
+	 * To prevent an RCU stall due to receiving too many signals by RT tasks,
+	 * count all signals regardless of their type.
+	 * Based on this counter, the RT scheduler will decide whether the task
+	 * should be throttled or not.
+	 */
+	if (tsk->policy == SCHED_FIFO || tsk->policy == SCHED_RR)
+		atomic_inc(&tsk->rt_signals_recv_count);
+
 	/* We only dequeue private signals from ourselves, we don't let
 	 * signalfd steal them
 	 */
-- 
2.43.0

Re: [syzbot] Test

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Subject: Test
Author: radoslaw.zielonek@gmail.com

#syz test https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git dccb07f2914cdab2ac3a5b6c98406f765acab803

---
 include/linux/sched.h |  7 +++++++
 kernel/sched/core.c   |  1 +
 kernel/sched/rt.c     | 26 +++++++++++++++++++++++---
 kernel/signal.c       |  9 +++++++++
 4 files changed, 40 insertions(+), 3 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 17cb0761ff65..123bc16ad3d0 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1121,6 +1121,13 @@ struct task_struct {
 	size_t				sas_ss_size;
 	unsigned int			sas_ss_flags;
 
+	/*
+	 * Number of signals received by an RT task between scheduling ticks.
+	 * This counter is used to throttle RT tasks when too many signals
+	 * (e.g., POSIX timers) are sent to the task, which can cause an RCU stall.
+	 */
+	atomic_t rt_signals_recv_count; /* used outside of the rq lock */
+
 	struct callback_head		*task_works;
 
 #ifdef CONFIG_AUDIT
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index d44efa0d0611..9def826bd35f 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4779,6 +4779,7 @@ int sched_fork(unsigned long clone_flags, struct task_struct *p)
 			p->policy = SCHED_NORMAL;
 			p->static_prio = NICE_TO_PRIO(0);
 			p->rt_priority = 0;
+			atomic_set(&p->rt_signals_recv_count, 0);
 		} else if (PRIO_TO_NICE(p->static_prio) < 0)
 			p->static_prio = NICE_TO_PRIO(0);
 
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 3261b067b67e..9b22d67d1746 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -24,6 +24,15 @@ int sysctl_sched_rt_period = 1000000;
  */
 int sysctl_sched_rt_runtime = 950000;
 
+/*
+ * To avoid an RCU stall due to a large number of signals received by RT tasks
+ * (e.g., POSIX timers), the RT task needs to be throttled.
+ * When the number of signals received by an RT task during a scheduling
+ * tick period exceeds the threshold, the RT task will be throttled.
+ * The value of 100 has not been thoroughly tested and may need adjustment.
+ */
+#define RT_RECV_SGINAL_THROTTLE_THRESHOLD 100
+
 #ifdef CONFIG_SYSCTL
 static int sysctl_sched_rr_timeslice = (MSEC_PER_SEC * RR_TIMESLICE) / HZ;
 static int sched_rt_handler(struct ctl_table *table, int write, void *buffer,
@@ -951,7 +960,7 @@ static inline int rt_se_prio(struct sched_rt_entity *rt_se)
 	return rt_task_of(rt_se)->prio;
 }
 
-static int sched_rt_runtime_exceeded(struct rt_rq *rt_rq)
+static int sched_rt_runtime_exceeded(struct rt_rq *rt_rq, int rt_signal_recv)
 {
 	u64 runtime = sched_rt_runtime(rt_rq);
 
@@ -966,7 +975,15 @@ static int sched_rt_runtime_exceeded(struct rt_rq *rt_rq)
 	if (runtime == RUNTIME_INF)
 		return 0;
 
-	if (rt_rq->rt_time > runtime) {
+	/*
+	 * When a large number of signals are sent to this task (e.g., POSIX timers)
+	 * the delta time deviates significantly from real time due to the overhead
+	 * of handling signals. For RT tasks, this can cause an RCU stall.
+	 * To avoid this, throttle the task when the number of signals received
+	 * exceeds a certain threshold.
+	 */
+	if (rt_rq->rt_time > runtime ||
+		rt_signal_recv >= RT_RECV_SGINAL_THROTTLE_THRESHOLD) {
 		struct rt_bandwidth *rt_b = sched_rt_bandwidth(rt_rq);
 
 		/*
@@ -1021,7 +1038,9 @@ static void update_curr_rt(struct rq *rq)
 		if (sched_rt_runtime(rt_rq) != RUNTIME_INF) {
 			raw_spin_lock(&rt_rq->rt_runtime_lock);
 			rt_rq->rt_time += delta_exec;
-			exceeded = sched_rt_runtime_exceeded(rt_rq);
+			exceeded = sched_rt_runtime_exceeded(
+						rt_rq,
+						atomic_read(&curr->rt_signals_recv_count));
 			if (exceeded)
 				resched_curr(rq);
 			raw_spin_unlock(&rt_rq->rt_runtime_lock);
@@ -1029,6 +1048,7 @@ static void update_curr_rt(struct rq *rq)
 				do_start_rt_bandwidth(sched_rt_bandwidth(rt_rq));
 		}
 	}
+	atomic_set(&curr->rt_signals_recv_count, 0);
 }
 
 static void
diff --git a/kernel/signal.c b/kernel/signal.c
index bdca529f0f7b..d58e0ba9336c 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -629,6 +629,15 @@ int dequeue_signal(struct task_struct *tsk, sigset_t *mask,
 	bool resched_timer = false;
 	int signr;
 
+	/*
+	 * To prevent an RCU stall due to receiving too many signals by RT tasks,
+	 * count all signals regardless of their type.
+	 * Based on this counter, the RT scheduler will decide whether the task
+	 * should be throttled or not.
+	 */
+	if (tsk->policy == SCHED_FIFO || tsk->policy == SCHED_RR)
+		atomic_inc(&tsk->rt_signals_recv_count);
+
 	/* We only dequeue private signals from ourselves, we don't let
 	 * signalfd steal them
 	 */
-- 
2.43.0

Re: [syzbot] Test

[syzbot]

For archival purposes, forwarding an incoming command email to
linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com.

***

Subject: Test
Author: radoslaw.zielonek@gmail.com

#syz test 

---
 include/linux/sched.h |  7 +++++++
 kernel/sched/core.c   |  1 +
 kernel/sched/rt.c     | 26 +++++++++++++++++++++++---
 kernel/signal.c       |  9 +++++++++
 4 files changed, 40 insertions(+), 3 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 17cb0761ff65..123bc16ad3d0 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1121,6 +1121,13 @@ struct task_struct {
 	size_t				sas_ss_size;
 	unsigned int			sas_ss_flags;
 
+	/*
+	 * Number of signals received by an RT task between scheduling ticks.
+	 * This counter is used to throttle RT tasks when too many signals
+	 * (e.g., POSIX timers) are sent to the task, which can cause an RCU stall.
+	 */
+	atomic_t rt_signals_recv_count; /* used outside of the rq lock */
+
 	struct callback_head		*task_works;
 
 #ifdef CONFIG_AUDIT
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index d44efa0d0611..9def826bd35f 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4779,6 +4779,7 @@ int sched_fork(unsigned long clone_flags, struct task_struct *p)
 			p->policy = SCHED_NORMAL;
 			p->static_prio = NICE_TO_PRIO(0);
 			p->rt_priority = 0;
+			atomic_set(&p->rt_signals_recv_count, 0);
 		} else if (PRIO_TO_NICE(p->static_prio) < 0)
 			p->static_prio = NICE_TO_PRIO(0);
 
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 3261b067b67e..9b22d67d1746 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -24,6 +24,15 @@ int sysctl_sched_rt_period = 1000000;
  */
 int sysctl_sched_rt_runtime = 950000;
 
+/*
+ * To avoid an RCU stall due to a large number of signals received by RT tasks
+ * (e.g., POSIX timers), the RT task needs to be throttled.
+ * When the number of signals received by an RT task during a scheduling
+ * tick period exceeds the threshold, the RT task will be throttled.
+ * The value of 100 has not been thoroughly tested and may need adjustment.
+ */
+#define RT_RECV_SGINAL_THROTTLE_THRESHOLD 100
+
 #ifdef CONFIG_SYSCTL
 static int sysctl_sched_rr_timeslice = (MSEC_PER_SEC * RR_TIMESLICE) / HZ;
 static int sched_rt_handler(struct ctl_table *table, int write, void *buffer,
@@ -951,7 +960,7 @@ static inline int rt_se_prio(struct sched_rt_entity *rt_se)
 	return rt_task_of(rt_se)->prio;
 }
 
-static int sched_rt_runtime_exceeded(struct rt_rq *rt_rq)
+static int sched_rt_runtime_exceeded(struct rt_rq *rt_rq, int rt_signal_recv)
 {
 	u64 runtime = sched_rt_runtime(rt_rq);
 
@@ -966,7 +975,15 @@ static int sched_rt_runtime_exceeded(struct rt_rq *rt_rq)
 	if (runtime == RUNTIME_INF)
 		return 0;
 
-	if (rt_rq->rt_time > runtime) {
+	/*
+	 * When a large number of signals are sent to this task (e.g., POSIX timers)
+	 * the delta time deviates significantly from real time due to the overhead
+	 * of handling signals. For RT tasks, this can cause an RCU stall.
+	 * To avoid this, throttle the task when the number of signals received
+	 * exceeds a certain threshold.
+	 */
+	if (rt_rq->rt_time > runtime ||
+		rt_signal_recv >= RT_RECV_SGINAL_THROTTLE_THRESHOLD) {
 		struct rt_bandwidth *rt_b = sched_rt_bandwidth(rt_rq);
 
 		/*
@@ -1021,7 +1038,9 @@ static void update_curr_rt(struct rq *rq)
 		if (sched_rt_runtime(rt_rq) != RUNTIME_INF) {
 			raw_spin_lock(&rt_rq->rt_runtime_lock);
 			rt_rq->rt_time += delta_exec;
-			exceeded = sched_rt_runtime_exceeded(rt_rq);
+			exceeded = sched_rt_runtime_exceeded(
+						rt_rq,
+						atomic_read(&curr->rt_signals_recv_count));
 			if (exceeded)
 				resched_curr(rq);
 			raw_spin_unlock(&rt_rq->rt_runtime_lock);
@@ -1029,6 +1048,7 @@ static void update_curr_rt(struct rq *rq)
 				do_start_rt_bandwidth(sched_rt_bandwidth(rt_rq));
 		}
 	}
+	atomic_set(&curr->rt_signals_recv_count, 0);
 }
 
 static void
diff --git a/kernel/signal.c b/kernel/signal.c
index bdca529f0f7b..d58e0ba9336c 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -629,6 +629,15 @@ int dequeue_signal(struct task_struct *tsk, sigset_t *mask,
 	bool resched_timer = false;
 	int signr;
 
+	/*
+	 * To prevent an RCU stall due to receiving too many signals by RT tasks,
+	 * count all signals regardless of their type.
+	 * Based on this counter, the RT scheduler will decide whether the task
+	 * should be throttled or not.
+	 */
+	if (tsk->policy == SCHED_FIFO || tsk->policy == SCHED_RR)
+		atomic_inc(&tsk->rt_signals_recv_count);
+
 	/* We only dequeue private signals from ourselves, we don't let
 	 * signalfd steal them
 	 */
-- 
2.43.0

Re: [syzbot] test

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Subject: test
Author: danielyangkang@gmail.com

#syz test

Re: [syzbot] test

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Subject: test
Author: danielyangkang@gmail.com

#syz test

Re: [syzbot] [usb?] [input?] WARNING in bcm5974_start_traffic/usb_submit_urb (2)

[syzbot]

syzbot suspects this issue was fixed by commit:

commit 503bbde34cc3dd2acd231f277ba70c3f9ed22e59
Author: Oliver Neukum <oneukum@suse.com>
Date:   Thu Jun 12 12:20:25 2025 +0000

    usb: core: usb_submit_urb: downgrade type check

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=16c6eb62580000
start commit:   e8ab83e34bdc Merge tag 'arm64-fixes' of git://git.kernel.o..
git tree:       upstream
kernel config:  https://syzkaller.appspot.com/x/.config?x=a9a25b7a36123454
dashboard link: https://syzkaller.appspot.com/bug?extid=b064b5599f18f7ebb1e1
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1514f0f4580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=11699a70580000

If the result looks correct, please mark the issue as fixed by replying with:

#syz fix: usb: core: usb_submit_urb: downgrade type check

For information about bisection process see: https://goo.gl/tpsmEJ#bisection