[syzbot] UBSAN: array-index-out-of-bounds in diWrite

[syzbot] UBSAN: array-index-out-of-bounds in diWrite

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    493ffd6605b2 Merge tag 'ucount-rlimits-cleanups-for-v5.19'..
git tree:       upstream
console+strace: https://syzkaller.appspot.com/x/log.txt?x=1512cd9a880000
kernel config:  https://syzkaller.appspot.com/x/.config?x=d19f5d16783f901
dashboard link: https://syzkaller.appspot.com/bug?extid=c1056fdfe414463fdb33
compiler:       Debian clang version 13.0.1-++20220126092033+75e33f71c2da-1~exp1~20220126212112.63, GNU ld (GNU Binutils for Debian) 2.35.2
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=12f431d2880000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1208894a880000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/f1ff6481e26f/disk-493ffd66.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/101bd3c7ae47/vmlinux-493ffd66.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/720c16671db9/mount_0.gz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+c1056fdfe414463fdb33@syzkaller.appspotmail.com

================================================================================
UBSAN: array-index-out-of-bounds in fs/jfs/jfs_imap.c:749:4
index 255 is out of range for type 'struct dtslot [128]'
CPU: 1 PID: 3606 Comm: syz-executor322 Not tainted 6.0.0-syzkaller-09423-g493ffd6605b2 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/11/2022
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0x1b1/0x28e lib/dump_stack.c:106
 ubsan_epilogue lib/ubsan.c:151 [inline]
 __ubsan_handle_out_of_bounds+0xdb/0x130 lib/ubsan.c:283
 diWrite+0x1311/0x1f80 fs/jfs/jfs_imap.c:749
 txCommit+0xa2e/0x6d40 fs/jfs/jfs_txnmgr.c:1250
 jfs_mkdir+0x911/0xb00 fs/jfs/namei.c:290
 vfs_mkdir+0x3b3/0x590 fs/namei.c:4013
 do_mkdirat+0x279/0x550 fs/namei.c:4038
 __do_sys_mkdirat fs/namei.c:4053 [inline]
 __se_sys_mkdirat fs/namei.c:4051 [inline]
 __x64_sys_mkdirat+0x85/0x90 fs/namei.c:4051
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x3d/0xb0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x63/0xcd
RIP: 0033:0x7f1a977dfe49
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 c0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffd8f230c48 EFLAGS: 00000246 ORIG_RAX: 0000000000000102
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f1a977dfe49
RDX: 00000000000001ff RSI: 00000000200000c0 RDI: ffffffffffffff9c
RBP: 00007f1a9779f610 R08: 0000000000000000 R09: 0000000000000000
R10: 00005555566302c0 R11: 0000000000000246 R12: 00000000f8008000
R13: 0000000000000000 R14: 00083878000000fc R15: 0000000000000000
 </TASK>
================================================================================


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Re: [syzbot] [jfs?] UBSAN: array-index-out-of-bounds in diWrite

[syzbot]

syzbot suspects this issue was fixed by commit:

commit 6f861765464f43a71462d52026fbddfc858239a5
Author: Jan Kara <jack@suse.cz>
Date:   Wed Nov 1 17:43:10 2023 +0000

    fs: Block writes to mounted block devices

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=17ec162be80000
start commit:   493ffd6605b2 Merge tag 'ucount-rlimits-cleanups-for-v5.19'..
git tree:       upstream
kernel config:  https://syzkaller.appspot.com/x/.config?x=d19f5d16783f901
dashboard link: https://syzkaller.appspot.com/bug?extid=c1056fdfe414463fdb33
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=12f431d2880000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1208894a880000

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

#syz fix: fs: Block writes to mounted block devices

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

Re: [syzbot] [jfs?] UBSAN: array-index-out-of-bounds in diWrite

[Jan Kara]

On Sat 13-01-24 23:18:05, syzbot wrote:
> syzbot suspects this issue was fixed by commit:
> 
> commit 6f861765464f43a71462d52026fbddfc858239a5
> Author: Jan Kara <jack@suse.cz>
> Date:   Wed Nov 1 17:43:10 2023 +0000
> 
>     fs: Block writes to mounted block devices
> 
> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=17ec162be80000
> start commit:   493ffd6605b2 Merge tag 'ucount-rlimits-cleanups-for-v5.19'..
> git tree:       upstream
> kernel config:  https://syzkaller.appspot.com/x/.config?x=d19f5d16783f901
> dashboard link: https://syzkaller.appspot.com/bug?extid=c1056fdfe414463fdb33
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=12f431d2880000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1208894a880000
> 
> If the result looks correct, please mark the issue as fixed by replying with:

Makes sense:

#syz fix: fs: Block writes to mounted block devices

								Honza
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR

Re: [syzbot] [jfs?] UBSAN: array-index-out-of-bounds in diWrite

[Christian Brauner]

On Mon, Jan 15, 2024 at 02:42:28PM +0100, Jan Kara wrote:
> On Sat 13-01-24 23:18:05, syzbot wrote:
> > syzbot suspects this issue was fixed by commit:
> > 
> > commit 6f861765464f43a71462d52026fbddfc858239a5
> > Author: Jan Kara <jack@suse.cz>
> > Date:   Wed Nov 1 17:43:10 2023 +0000
> > 
> >     fs: Block writes to mounted block devices
> > 
> > bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=17ec162be80000
> > start commit:   493ffd6605b2 Merge tag 'ucount-rlimits-cleanups-for-v5.19'..
> > git tree:       upstream
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=d19f5d16783f901
> > dashboard link: https://syzkaller.appspot.com/bug?extid=c1056fdfe414463fdb33
> > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=12f431d2880000
> > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1208894a880000
> > 
> > If the result looks correct, please mark the issue as fixed by replying with:
> 
> Makes sense:
> 
> #syz fix: fs: Block writes to mounted block devices

I love how many things this closes. This is awesome!

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#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

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#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

[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 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

[syzbot]

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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