The patch below does not apply to the 6.6-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable(a)vger.kernel.org>.
To reproduce the conflict and resubmit, you may use the following commands:
git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.6.y
git checkout FETCH_HEAD
git cherry-pick -x 0c43094f8cc9d3d99d835c0ac9c4fe1ccc62babd
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable(a)vger.kernel.org>' --in-reply-to '2025101614-turbofan-sufferer-957e@gregkh' --subject-prefix 'PATCH 6.6.y' HEAD^..
Possible dependencies:
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From 0c43094f8cc9d3d99d835c0ac9c4fe1ccc62babd Mon Sep 17 00:00:00 2001
From: Nam Cao <namcao(a)linutronix.de>
Date: Tue, 15 Jul 2025 14:46:34 +0200
Subject: [PATCH] eventpoll: Replace rwlock with spinlock
The ready event list of an epoll object is protected by read-write
semaphore:
- The consumer (waiter) acquires the write lock and takes items.
- the producer (waker) takes the read lock and adds items.
The point of this design is enabling epoll to scale well with large number
of producers, as multiple producers can hold the read lock at the same
time.
Unfortunately, this implementation may cause scheduling priority inversion
problem. Suppose the consumer has higher scheduling priority than the
producer. The consumer needs to acquire the write lock, but may be blocked
by the producer holding the read lock. Since read-write semaphore does not
support priority-boosting for the readers (even with CONFIG_PREEMPT_RT=y),
we have a case of priority inversion: a higher priority consumer is blocked
by a lower priority producer. This problem was reported in [1].
Furthermore, this could also cause stall problem, as described in [2].
Fix this problem by replacing rwlock with spinlock.
This reduces the event bandwidth, as the producers now have to contend with
each other for the spinlock. According to the benchmark from
https://github.com/rouming/test-tools/blob/master/stress-epoll.c:
On 12 x86 CPUs:
Before After Diff
threads events/ms events/ms
8 7162 4956 -31%
16 8733 5383 -38%
32 7968 5572 -30%
64 10652 5739 -46%
128 11236 5931 -47%
On 4 riscv CPUs:
Before After Diff
threads events/ms events/ms
8 2958 2833 -4%
16 3323 3097 -7%
32 3451 3240 -6%
64 3554 3178 -11%
128 3601 3235 -10%
Although the numbers look bad, it should be noted that this benchmark
creates multiple threads who do nothing except constantly generating new
epoll events, thus contention on the spinlock is high. For real workload,
the event rate is likely much lower, and the performance drop is not as
bad.
Using another benchmark (perf bench epoll wait) where spinlock contention
is lower, improvement is even observed on x86:
On 12 x86 CPUs:
Before: Averaged 110279 operations/sec (+- 1.09%), total secs = 8
After: Averaged 114577 operations/sec (+- 2.25%), total secs = 8
On 4 riscv CPUs:
Before: Averaged 175767 operations/sec (+- 0.62%), total secs = 8
After: Averaged 167396 operations/sec (+- 0.23%), total secs = 8
In conclusion, no one is likely to be upset over this change. After all,
spinlock was used originally for years, and the commit which converted to
rwlock didn't mention a real workload, just that the benchmark numbers are
nice.
This patch is not exactly the revert of commit a218cc491420 ("epoll: use
rwlock in order to reduce ep_poll_callback() contention"), because git
revert conflicts in some places which are not obvious on the resolution.
This patch is intended to be backported, therefore go with the obvious
approach:
- Replace rwlock_t with spinlock_t one to one
- Delete list_add_tail_lockless() and chain_epi_lockless(). These were
introduced to allow producers to concurrently add items to the list.
But now that spinlock no longer allows producers to touch the event
list concurrently, these two functions are not necessary anymore.
Fixes: a218cc491420 ("epoll: use rwlock in order to reduce ep_poll_callback() contention")
Signed-off-by: Nam Cao <namcao(a)linutronix.de>
Link: https://lore.kernel.org/ec92458ea357ec503c737ead0f10b2c6e4c37d47.1752581388…
Tested-by: K Prateek Nayak <kprateek.nayak(a)amd.com>
Cc: stable(a)vger.kernel.org
Reported-by: Frederic Weisbecker <frederic(a)kernel.org>
Closes: https://lore.kernel.org/linux-rt-users/20210825132754.GA895675@lothringen/ [1]
Reported-by: Valentin Schneider <vschneid(a)redhat.com>
Closes: https://lore.kernel.org/linux-rt-users/xhsmhttqvnall.mognet@vschneid.remote… [2]
Signed-off-by: Christian Brauner <brauner(a)kernel.org>
diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index b22d6f819f78..ee7c4b683ec3 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -46,10 +46,10 @@
*
* 1) epnested_mutex (mutex)
* 2) ep->mtx (mutex)
- * 3) ep->lock (rwlock)
+ * 3) ep->lock (spinlock)
*
* The acquire order is the one listed above, from 1 to 3.
- * We need a rwlock (ep->lock) because we manipulate objects
+ * We need a spinlock (ep->lock) because we manipulate objects
* from inside the poll callback, that might be triggered from
* a wake_up() that in turn might be called from IRQ context.
* So we can't sleep inside the poll callback and hence we need
@@ -195,7 +195,7 @@ struct eventpoll {
struct list_head rdllist;
/* Lock which protects rdllist and ovflist */
- rwlock_t lock;
+ spinlock_t lock;
/* RB tree root used to store monitored fd structs */
struct rb_root_cached rbr;
@@ -741,10 +741,10 @@ static void ep_start_scan(struct eventpoll *ep, struct list_head *txlist)
* in a lockless way.
*/
lockdep_assert_irqs_enabled();
- write_lock_irq(&ep->lock);
+ spin_lock_irq(&ep->lock);
list_splice_init(&ep->rdllist, txlist);
WRITE_ONCE(ep->ovflist, NULL);
- write_unlock_irq(&ep->lock);
+ spin_unlock_irq(&ep->lock);
}
static void ep_done_scan(struct eventpoll *ep,
@@ -752,7 +752,7 @@ static void ep_done_scan(struct eventpoll *ep,
{
struct epitem *epi, *nepi;
- write_lock_irq(&ep->lock);
+ spin_lock_irq(&ep->lock);
/*
* During the time we spent inside the "sproc" callback, some
* other events might have been queued by the poll callback.
@@ -793,7 +793,7 @@ static void ep_done_scan(struct eventpoll *ep,
wake_up(&ep->wq);
}
- write_unlock_irq(&ep->lock);
+ spin_unlock_irq(&ep->lock);
}
static void ep_get(struct eventpoll *ep)
@@ -868,10 +868,10 @@ static bool __ep_remove(struct eventpoll *ep, struct epitem *epi, bool force)
rb_erase_cached(&epi->rbn, &ep->rbr);
- write_lock_irq(&ep->lock);
+ spin_lock_irq(&ep->lock);
if (ep_is_linked(epi))
list_del_init(&epi->rdllink);
- write_unlock_irq(&ep->lock);
+ spin_unlock_irq(&ep->lock);
wakeup_source_unregister(ep_wakeup_source(epi));
/*
@@ -1152,7 +1152,7 @@ static int ep_alloc(struct eventpoll **pep)
return -ENOMEM;
mutex_init(&ep->mtx);
- rwlock_init(&ep->lock);
+ spin_lock_init(&ep->lock);
init_waitqueue_head(&ep->wq);
init_waitqueue_head(&ep->poll_wait);
INIT_LIST_HEAD(&ep->rdllist);
@@ -1239,100 +1239,10 @@ struct file *get_epoll_tfile_raw_ptr(struct file *file, int tfd,
}
#endif /* CONFIG_KCMP */
-/*
- * Adds a new entry to the tail of the list in a lockless way, i.e.
- * multiple CPUs are allowed to call this function concurrently.
- *
- * Beware: it is necessary to prevent any other modifications of the
- * existing list until all changes are completed, in other words
- * concurrent list_add_tail_lockless() calls should be protected
- * with a read lock, where write lock acts as a barrier which
- * makes sure all list_add_tail_lockless() calls are fully
- * completed.
- *
- * Also an element can be locklessly added to the list only in one
- * direction i.e. either to the tail or to the head, otherwise
- * concurrent access will corrupt the list.
- *
- * Return: %false if element has been already added to the list, %true
- * otherwise.
- */
-static inline bool list_add_tail_lockless(struct list_head *new,
- struct list_head *head)
-{
- struct list_head *prev;
-
- /*
- * This is simple 'new->next = head' operation, but cmpxchg()
- * is used in order to detect that same element has been just
- * added to the list from another CPU: the winner observes
- * new->next == new.
- */
- if (!try_cmpxchg(&new->next, &new, head))
- return false;
-
- /*
- * Initially ->next of a new element must be updated with the head
- * (we are inserting to the tail) and only then pointers are atomically
- * exchanged. XCHG guarantees memory ordering, thus ->next should be
- * updated before pointers are actually swapped and pointers are
- * swapped before prev->next is updated.
- */
-
- prev = xchg(&head->prev, new);
-
- /*
- * It is safe to modify prev->next and new->prev, because a new element
- * is added only to the tail and new->next is updated before XCHG.
- */
-
- prev->next = new;
- new->prev = prev;
-
- return true;
-}
-
-/*
- * Chains a new epi entry to the tail of the ep->ovflist in a lockless way,
- * i.e. multiple CPUs are allowed to call this function concurrently.
- *
- * Return: %false if epi element has been already chained, %true otherwise.
- */
-static inline bool chain_epi_lockless(struct epitem *epi)
-{
- struct eventpoll *ep = epi->ep;
-
- /* Fast preliminary check */
- if (epi->next != EP_UNACTIVE_PTR)
- return false;
-
- /* Check that the same epi has not been just chained from another CPU */
- if (cmpxchg(&epi->next, EP_UNACTIVE_PTR, NULL) != EP_UNACTIVE_PTR)
- return false;
-
- /* Atomically exchange tail */
- epi->next = xchg(&ep->ovflist, epi);
-
- return true;
-}
-
/*
* This is the callback that is passed to the wait queue wakeup
* mechanism. It is called by the stored file descriptors when they
* have events to report.
- *
- * This callback takes a read lock in order not to contend with concurrent
- * events from another file descriptor, thus all modifications to ->rdllist
- * or ->ovflist are lockless. Read lock is paired with the write lock from
- * ep_start/done_scan(), which stops all list modifications and guarantees
- * that lists state is seen correctly.
- *
- * Another thing worth to mention is that ep_poll_callback() can be called
- * concurrently for the same @epi from different CPUs if poll table was inited
- * with several wait queues entries. Plural wakeup from different CPUs of a
- * single wait queue is serialized by wq.lock, but the case when multiple wait
- * queues are used should be detected accordingly. This is detected using
- * cmpxchg() operation.
*/
static int ep_poll_callback(wait_queue_entry_t *wait, unsigned mode, int sync, void *key)
{
@@ -1343,7 +1253,7 @@ static int ep_poll_callback(wait_queue_entry_t *wait, unsigned mode, int sync, v
unsigned long flags;
int ewake = 0;
- read_lock_irqsave(&ep->lock, flags);
+ spin_lock_irqsave(&ep->lock, flags);
ep_set_busy_poll_napi_id(epi);
@@ -1372,12 +1282,15 @@ static int ep_poll_callback(wait_queue_entry_t *wait, unsigned mode, int sync, v
* chained in ep->ovflist and requeued later on.
*/
if (READ_ONCE(ep->ovflist) != EP_UNACTIVE_PTR) {
- if (chain_epi_lockless(epi))
+ if (epi->next == EP_UNACTIVE_PTR) {
+ epi->next = READ_ONCE(ep->ovflist);
+ WRITE_ONCE(ep->ovflist, epi);
ep_pm_stay_awake_rcu(epi);
+ }
} else if (!ep_is_linked(epi)) {
/* In the usual case, add event to ready list. */
- if (list_add_tail_lockless(&epi->rdllink, &ep->rdllist))
- ep_pm_stay_awake_rcu(epi);
+ list_add_tail(&epi->rdllink, &ep->rdllist);
+ ep_pm_stay_awake_rcu(epi);
}
/*
@@ -1410,7 +1323,7 @@ static int ep_poll_callback(wait_queue_entry_t *wait, unsigned mode, int sync, v
pwake++;
out_unlock:
- read_unlock_irqrestore(&ep->lock, flags);
+ spin_unlock_irqrestore(&ep->lock, flags);
/* We have to call this outside the lock */
if (pwake)
@@ -1745,7 +1658,7 @@ static int ep_insert(struct eventpoll *ep, const struct epoll_event *event,
}
/* We have to drop the new item inside our item list to keep track of it */
- write_lock_irq(&ep->lock);
+ spin_lock_irq(&ep->lock);
/* record NAPI ID of new item if present */
ep_set_busy_poll_napi_id(epi);
@@ -1762,7 +1675,7 @@ static int ep_insert(struct eventpoll *ep, const struct epoll_event *event,
pwake++;
}
- write_unlock_irq(&ep->lock);
+ spin_unlock_irq(&ep->lock);
/* We have to call this outside the lock */
if (pwake)
@@ -1826,7 +1739,7 @@ static int ep_modify(struct eventpoll *ep, struct epitem *epi,
* list, push it inside.
*/
if (ep_item_poll(epi, &pt, 1)) {
- write_lock_irq(&ep->lock);
+ spin_lock_irq(&ep->lock);
if (!ep_is_linked(epi)) {
list_add_tail(&epi->rdllink, &ep->rdllist);
ep_pm_stay_awake(epi);
@@ -1837,7 +1750,7 @@ static int ep_modify(struct eventpoll *ep, struct epitem *epi,
if (waitqueue_active(&ep->poll_wait))
pwake++;
}
- write_unlock_irq(&ep->lock);
+ spin_unlock_irq(&ep->lock);
}
/* We have to call this outside the lock */
@@ -2089,7 +2002,7 @@ static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events,
init_wait(&wait);
wait.func = ep_autoremove_wake_function;
- write_lock_irq(&ep->lock);
+ spin_lock_irq(&ep->lock);
/*
* Barrierless variant, waitqueue_active() is called under
* the same lock on wakeup ep_poll_callback() side, so it
@@ -2108,7 +2021,7 @@ static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events,
if (!eavail)
__add_wait_queue_exclusive(&ep->wq, &wait);
- write_unlock_irq(&ep->lock);
+ spin_unlock_irq(&ep->lock);
if (!eavail)
timed_out = !ep_schedule_timeout(to) ||
@@ -2124,7 +2037,7 @@ static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events,
eavail = 1;
if (!list_empty_careful(&wait.entry)) {
- write_lock_irq(&ep->lock);
+ spin_lock_irq(&ep->lock);
/*
* If the thread timed out and is not on the wait queue,
* it means that the thread was woken up after its
@@ -2135,7 +2048,7 @@ static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events,
if (timed_out)
eavail = list_empty(&wait.entry);
__remove_wait_queue(&ep->wq, &wait);
- write_unlock_irq(&ep->lock);
+ spin_unlock_irq(&ep->lock);
}
}
}
Hi Marek,
Thank you very much for fixing this bug and for your contribution.
Since my original report was not posted to a public mailing list, I would
appreciate it if you could add the following credit to this patch:
Reported-by: Shuangpeng Bai <SJB7183(a)psu.edu>
Thanks again!
Best regards,
Shuangpeng
The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable(a)vger.kernel.org>.
To reproduce the conflict and resubmit, you may use the following commands:
git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x f965d111e68f4a993cc44d487d416e3d954eea11
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable(a)vger.kernel.org>' --in-reply-to '2025101655-grandma-populate-0fb4@gregkh' --subject-prefix 'PATCH 5.15.y' HEAD^..
Possible dependencies:
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From f965d111e68f4a993cc44d487d416e3d954eea11 Mon Sep 17 00:00:00 2001
From: "Rafael J. Wysocki" <rafael.j.wysocki(a)intel.com>
Date: Fri, 26 Sep 2025 12:19:41 +0200
Subject: [PATCH] cpufreq: CPPC: Avoid using CPUFREQ_ETERNAL as transition
delay
If cppc_get_transition_latency() returns CPUFREQ_ETERNAL to indicate a
failure to retrieve the transition latency value from the platform
firmware, the CPPC cpufreq driver will use that value (converted to
microseconds) as the policy transition delay, but it is way too large
for any practical use.
Address this by making the driver use the cpufreq's default
transition latency value (in microseconds) as the transition delay
if CPUFREQ_ETERNAL is returned by cppc_get_transition_latency().
Fixes: d4f3388afd48 ("cpufreq / CPPC: Set platform specific transition_delay_us")
Cc: 5.19+ <stable(a)vger.kernel.org> # 5.19
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki(a)intel.com>
Reviewed-by: Mario Limonciello (AMD) <superm1(a)kernel.org>
Reviewed-by: Jie Zhan <zhanjie9(a)hisilicon.com>
Acked-by: Viresh Kumar <viresh.kumar(a)linaro.org>
Reviewed-by: Qais Yousef <qyousef(a)layalina.io>
diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c
index 12de0ac7bbaf..b71946937c52 100644
--- a/drivers/cpufreq/cppc_cpufreq.c
+++ b/drivers/cpufreq/cppc_cpufreq.c
@@ -308,6 +308,16 @@ static int cppc_verify_policy(struct cpufreq_policy_data *policy)
return 0;
}
+static unsigned int __cppc_cpufreq_get_transition_delay_us(unsigned int cpu)
+{
+ unsigned int transition_latency_ns = cppc_get_transition_latency(cpu);
+
+ if (transition_latency_ns == CPUFREQ_ETERNAL)
+ return CPUFREQ_DEFAULT_TRANSITION_LATENCY_NS / NSEC_PER_USEC;
+
+ return transition_latency_ns / NSEC_PER_USEC;
+}
+
/*
* The PCC subspace describes the rate at which platform can accept commands
* on the shared PCC channel (including READs which do not count towards freq
@@ -330,12 +340,12 @@ static unsigned int cppc_cpufreq_get_transition_delay_us(unsigned int cpu)
return 10000;
}
}
- return cppc_get_transition_latency(cpu) / NSEC_PER_USEC;
+ return __cppc_cpufreq_get_transition_delay_us(cpu);
}
#else
static unsigned int cppc_cpufreq_get_transition_delay_us(unsigned int cpu)
{
- return cppc_get_transition_latency(cpu) / NSEC_PER_USEC;
+ return __cppc_cpufreq_get_transition_delay_us(cpu);
}
#endif
The patch below does not apply to the 6.1-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable(a)vger.kernel.org>.
To reproduce the conflict and resubmit, you may use the following commands:
git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.1.y
git checkout FETCH_HEAD
git cherry-pick -x f965d111e68f4a993cc44d487d416e3d954eea11
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable(a)vger.kernel.org>' --in-reply-to '2025101609-footsore-ensnare-d320@gregkh' --subject-prefix 'PATCH 6.1.y' HEAD^..
Possible dependencies:
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From f965d111e68f4a993cc44d487d416e3d954eea11 Mon Sep 17 00:00:00 2001
From: "Rafael J. Wysocki" <rafael.j.wysocki(a)intel.com>
Date: Fri, 26 Sep 2025 12:19:41 +0200
Subject: [PATCH] cpufreq: CPPC: Avoid using CPUFREQ_ETERNAL as transition
delay
If cppc_get_transition_latency() returns CPUFREQ_ETERNAL to indicate a
failure to retrieve the transition latency value from the platform
firmware, the CPPC cpufreq driver will use that value (converted to
microseconds) as the policy transition delay, but it is way too large
for any practical use.
Address this by making the driver use the cpufreq's default
transition latency value (in microseconds) as the transition delay
if CPUFREQ_ETERNAL is returned by cppc_get_transition_latency().
Fixes: d4f3388afd48 ("cpufreq / CPPC: Set platform specific transition_delay_us")
Cc: 5.19+ <stable(a)vger.kernel.org> # 5.19
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki(a)intel.com>
Reviewed-by: Mario Limonciello (AMD) <superm1(a)kernel.org>
Reviewed-by: Jie Zhan <zhanjie9(a)hisilicon.com>
Acked-by: Viresh Kumar <viresh.kumar(a)linaro.org>
Reviewed-by: Qais Yousef <qyousef(a)layalina.io>
diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c
index 12de0ac7bbaf..b71946937c52 100644
--- a/drivers/cpufreq/cppc_cpufreq.c
+++ b/drivers/cpufreq/cppc_cpufreq.c
@@ -308,6 +308,16 @@ static int cppc_verify_policy(struct cpufreq_policy_data *policy)
return 0;
}
+static unsigned int __cppc_cpufreq_get_transition_delay_us(unsigned int cpu)
+{
+ unsigned int transition_latency_ns = cppc_get_transition_latency(cpu);
+
+ if (transition_latency_ns == CPUFREQ_ETERNAL)
+ return CPUFREQ_DEFAULT_TRANSITION_LATENCY_NS / NSEC_PER_USEC;
+
+ return transition_latency_ns / NSEC_PER_USEC;
+}
+
/*
* The PCC subspace describes the rate at which platform can accept commands
* on the shared PCC channel (including READs which do not count towards freq
@@ -330,12 +340,12 @@ static unsigned int cppc_cpufreq_get_transition_delay_us(unsigned int cpu)
return 10000;
}
}
- return cppc_get_transition_latency(cpu) / NSEC_PER_USEC;
+ return __cppc_cpufreq_get_transition_delay_us(cpu);
}
#else
static unsigned int cppc_cpufreq_get_transition_delay_us(unsigned int cpu)
{
- return cppc_get_transition_latency(cpu) / NSEC_PER_USEC;
+ return __cppc_cpufreq_get_transition_delay_us(cpu);
}
#endif
The patch below does not apply to the 6.6-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable(a)vger.kernel.org>.
To reproduce the conflict and resubmit, you may use the following commands:
git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.6.y
git checkout FETCH_HEAD
git cherry-pick -x f965d111e68f4a993cc44d487d416e3d954eea11
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable(a)vger.kernel.org>' --in-reply-to '2025101609-unmoved-thud-9d3a@gregkh' --subject-prefix 'PATCH 6.6.y' HEAD^..
Possible dependencies:
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From f965d111e68f4a993cc44d487d416e3d954eea11 Mon Sep 17 00:00:00 2001
From: "Rafael J. Wysocki" <rafael.j.wysocki(a)intel.com>
Date: Fri, 26 Sep 2025 12:19:41 +0200
Subject: [PATCH] cpufreq: CPPC: Avoid using CPUFREQ_ETERNAL as transition
delay
If cppc_get_transition_latency() returns CPUFREQ_ETERNAL to indicate a
failure to retrieve the transition latency value from the platform
firmware, the CPPC cpufreq driver will use that value (converted to
microseconds) as the policy transition delay, but it is way too large
for any practical use.
Address this by making the driver use the cpufreq's default
transition latency value (in microseconds) as the transition delay
if CPUFREQ_ETERNAL is returned by cppc_get_transition_latency().
Fixes: d4f3388afd48 ("cpufreq / CPPC: Set platform specific transition_delay_us")
Cc: 5.19+ <stable(a)vger.kernel.org> # 5.19
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki(a)intel.com>
Reviewed-by: Mario Limonciello (AMD) <superm1(a)kernel.org>
Reviewed-by: Jie Zhan <zhanjie9(a)hisilicon.com>
Acked-by: Viresh Kumar <viresh.kumar(a)linaro.org>
Reviewed-by: Qais Yousef <qyousef(a)layalina.io>
diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c
index 12de0ac7bbaf..b71946937c52 100644
--- a/drivers/cpufreq/cppc_cpufreq.c
+++ b/drivers/cpufreq/cppc_cpufreq.c
@@ -308,6 +308,16 @@ static int cppc_verify_policy(struct cpufreq_policy_data *policy)
return 0;
}
+static unsigned int __cppc_cpufreq_get_transition_delay_us(unsigned int cpu)
+{
+ unsigned int transition_latency_ns = cppc_get_transition_latency(cpu);
+
+ if (transition_latency_ns == CPUFREQ_ETERNAL)
+ return CPUFREQ_DEFAULT_TRANSITION_LATENCY_NS / NSEC_PER_USEC;
+
+ return transition_latency_ns / NSEC_PER_USEC;
+}
+
/*
* The PCC subspace describes the rate at which platform can accept commands
* on the shared PCC channel (including READs which do not count towards freq
@@ -330,12 +340,12 @@ static unsigned int cppc_cpufreq_get_transition_delay_us(unsigned int cpu)
return 10000;
}
}
- return cppc_get_transition_latency(cpu) / NSEC_PER_USEC;
+ return __cppc_cpufreq_get_transition_delay_us(cpu);
}
#else
static unsigned int cppc_cpufreq_get_transition_delay_us(unsigned int cpu)
{
- return cppc_get_transition_latency(cpu) / NSEC_PER_USEC;
+ return __cppc_cpufreq_get_transition_delay_us(cpu);
}
#endif
The patch below does not apply to the 5.10-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable(a)vger.kernel.org>.
To reproduce the conflict and resubmit, you may use the following commands:
git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.10.y
git checkout FETCH_HEAD
git cherry-pick -x 06d712d297649f48ebf1381d19bd24e942813b37
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable(a)vger.kernel.org>' --in-reply-to '2025101657-rule-straw-2a51@gregkh' --subject-prefix 'PATCH 5.10.y' HEAD^..
Possible dependencies:
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From 06d712d297649f48ebf1381d19bd24e942813b37 Mon Sep 17 00:00:00 2001
From: Yu Kuai <yukuai3(a)huawei.com>
Date: Wed, 10 Sep 2025 14:30:45 +0800
Subject: [PATCH] blk-crypto: fix missing blktrace bio split events
trace_block_split() is missing, resulting in blktrace inability to catch
BIO split events and making it harder to analyze the BIO sequence.
Cc: stable(a)vger.kernel.org
Fixes: 488f6682c832 ("block: blk-crypto-fallback for Inline Encryption")
Signed-off-by: Yu Kuai <yukuai3(a)huawei.com>
Reviewed-by: Bart Van Assche <bvanassche(a)acm.org>
Reviewed-by: Christoph Hellwig <hch(a)lst.de>
Signed-off-by: Jens Axboe <axboe(a)kernel.dk>
diff --git a/block/blk-crypto-fallback.c b/block/blk-crypto-fallback.c
index dbc2d8784dab..27fa1ec4b264 100644
--- a/block/blk-crypto-fallback.c
+++ b/block/blk-crypto-fallback.c
@@ -18,6 +18,7 @@
#include <linux/module.h>
#include <linux/random.h>
#include <linux/scatterlist.h>
+#include <trace/events/block.h>
#include "blk-cgroup.h"
#include "blk-crypto-internal.h"
@@ -230,7 +231,9 @@ static bool blk_crypto_fallback_split_bio_if_needed(struct bio **bio_ptr)
bio->bi_status = BLK_STS_RESOURCE;
return false;
}
+
bio_chain(split_bio, bio);
+ trace_block_split(split_bio, bio->bi_iter.bi_sector);
submit_bio_noacct(bio);
*bio_ptr = split_bio;
}
The patch below does not apply to the 6.12-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable(a)vger.kernel.org>.
To reproduce the conflict and resubmit, you may use the following commands:
git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.12.y
git checkout FETCH_HEAD
git cherry-pick -x f965d111e68f4a993cc44d487d416e3d954eea11
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable(a)vger.kernel.org>' --in-reply-to '2025101610-twistable-shaping-5da2@gregkh' --subject-prefix 'PATCH 6.12.y' HEAD^..
Possible dependencies:
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From f965d111e68f4a993cc44d487d416e3d954eea11 Mon Sep 17 00:00:00 2001
From: "Rafael J. Wysocki" <rafael.j.wysocki(a)intel.com>
Date: Fri, 26 Sep 2025 12:19:41 +0200
Subject: [PATCH] cpufreq: CPPC: Avoid using CPUFREQ_ETERNAL as transition
delay
If cppc_get_transition_latency() returns CPUFREQ_ETERNAL to indicate a
failure to retrieve the transition latency value from the platform
firmware, the CPPC cpufreq driver will use that value (converted to
microseconds) as the policy transition delay, but it is way too large
for any practical use.
Address this by making the driver use the cpufreq's default
transition latency value (in microseconds) as the transition delay
if CPUFREQ_ETERNAL is returned by cppc_get_transition_latency().
Fixes: d4f3388afd48 ("cpufreq / CPPC: Set platform specific transition_delay_us")
Cc: 5.19+ <stable(a)vger.kernel.org> # 5.19
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki(a)intel.com>
Reviewed-by: Mario Limonciello (AMD) <superm1(a)kernel.org>
Reviewed-by: Jie Zhan <zhanjie9(a)hisilicon.com>
Acked-by: Viresh Kumar <viresh.kumar(a)linaro.org>
Reviewed-by: Qais Yousef <qyousef(a)layalina.io>
diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c
index 12de0ac7bbaf..b71946937c52 100644
--- a/drivers/cpufreq/cppc_cpufreq.c
+++ b/drivers/cpufreq/cppc_cpufreq.c
@@ -308,6 +308,16 @@ static int cppc_verify_policy(struct cpufreq_policy_data *policy)
return 0;
}
+static unsigned int __cppc_cpufreq_get_transition_delay_us(unsigned int cpu)
+{
+ unsigned int transition_latency_ns = cppc_get_transition_latency(cpu);
+
+ if (transition_latency_ns == CPUFREQ_ETERNAL)
+ return CPUFREQ_DEFAULT_TRANSITION_LATENCY_NS / NSEC_PER_USEC;
+
+ return transition_latency_ns / NSEC_PER_USEC;
+}
+
/*
* The PCC subspace describes the rate at which platform can accept commands
* on the shared PCC channel (including READs which do not count towards freq
@@ -330,12 +340,12 @@ static unsigned int cppc_cpufreq_get_transition_delay_us(unsigned int cpu)
return 10000;
}
}
- return cppc_get_transition_latency(cpu) / NSEC_PER_USEC;
+ return __cppc_cpufreq_get_transition_delay_us(cpu);
}
#else
static unsigned int cppc_cpufreq_get_transition_delay_us(unsigned int cpu)
{
- return cppc_get_transition_latency(cpu) / NSEC_PER_USEC;
+ return __cppc_cpufreq_get_transition_delay_us(cpu);
}
#endif
The patch below does not apply to the 5.4-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable(a)vger.kernel.org>.
To reproduce the conflict and resubmit, you may use the following commands:
git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.4.y
git checkout FETCH_HEAD
git cherry-pick -x dff4f9ff5d7f289e4545cc936362e01ed3252742
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable(a)vger.kernel.org>' --in-reply-to '2025101644-legacy-starch-6a67@gregkh' --subject-prefix 'PATCH 5.4.y' HEAD^..
Possible dependencies:
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From dff4f9ff5d7f289e4545cc936362e01ed3252742 Mon Sep 17 00:00:00 2001
From: Anderson Nascimento <anderson(a)allelesecurity.com>
Date: Mon, 8 Sep 2025 09:49:02 -0300
Subject: [PATCH] btrfs: avoid potential out-of-bounds in btrfs_encode_fh()
The function btrfs_encode_fh() does not properly account for the three
cases it handles.
Before writing to the file handle (fh), the function only returns to the
user BTRFS_FID_SIZE_NON_CONNECTABLE (5 dwords, 20 bytes) or
BTRFS_FID_SIZE_CONNECTABLE (8 dwords, 32 bytes).
However, when a parent exists and the root ID of the parent and the
inode are different, the function writes BTRFS_FID_SIZE_CONNECTABLE_ROOT
(10 dwords, 40 bytes).
If *max_len is not large enough, this write goes out of bounds because
BTRFS_FID_SIZE_CONNECTABLE_ROOT is greater than
BTRFS_FID_SIZE_CONNECTABLE originally returned.
This results in an 8-byte out-of-bounds write at
fid->parent_root_objectid = parent_root_id.
A previous attempt to fix this issue was made but was lost.
https://lore.kernel.org/all/4CADAEEC020000780001B32C@vpn.id2.novell.com/
Although this issue does not seem to be easily triggerable, it is a
potential memory corruption bug that should be fixed. This patch
resolves the issue by ensuring the function returns the appropriate size
for all three cases and validates that *max_len is large enough before
writing any data.
Fixes: be6e8dc0ba84 ("NFS support for btrfs - v3")
CC: stable(a)vger.kernel.org # 3.0+
Signed-off-by: Anderson Nascimento <anderson(a)allelesecurity.com>
Reviewed-by: David Sterba <dsterba(a)suse.com>
Signed-off-by: David Sterba <dsterba(a)suse.com>
diff --git a/fs/btrfs/export.c b/fs/btrfs/export.c
index d062ac521051..230d9326b685 100644
--- a/fs/btrfs/export.c
+++ b/fs/btrfs/export.c
@@ -23,7 +23,11 @@ static int btrfs_encode_fh(struct inode *inode, u32 *fh, int *max_len,
int type;
if (parent && (len < BTRFS_FID_SIZE_CONNECTABLE)) {
- *max_len = BTRFS_FID_SIZE_CONNECTABLE;
+ if (btrfs_root_id(BTRFS_I(inode)->root) !=
+ btrfs_root_id(BTRFS_I(parent)->root))
+ *max_len = BTRFS_FID_SIZE_CONNECTABLE_ROOT;
+ else
+ *max_len = BTRFS_FID_SIZE_CONNECTABLE;
return FILEID_INVALID;
} else if (len < BTRFS_FID_SIZE_NON_CONNECTABLE) {
*max_len = BTRFS_FID_SIZE_NON_CONNECTABLE;
@@ -45,6 +49,8 @@ static int btrfs_encode_fh(struct inode *inode, u32 *fh, int *max_len,
parent_root_id = btrfs_root_id(BTRFS_I(parent)->root);
if (parent_root_id != fid->root_objectid) {
+ if (*max_len < BTRFS_FID_SIZE_CONNECTABLE_ROOT)
+ return FILEID_INVALID;
fid->parent_root_objectid = parent_root_id;
len = BTRFS_FID_SIZE_CONNECTABLE_ROOT;
type = FILEID_BTRFS_WITH_PARENT_ROOT;
The patch below does not apply to the 5.10-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable(a)vger.kernel.org>.
To reproduce the conflict and resubmit, you may use the following commands:
git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.10.y
git checkout FETCH_HEAD
git cherry-pick -x dff4f9ff5d7f289e4545cc936362e01ed3252742
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable(a)vger.kernel.org>' --in-reply-to '2025101645-ceremony-playlist-e997@gregkh' --subject-prefix 'PATCH 5.10.y' HEAD^..
Possible dependencies:
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From dff4f9ff5d7f289e4545cc936362e01ed3252742 Mon Sep 17 00:00:00 2001
From: Anderson Nascimento <anderson(a)allelesecurity.com>
Date: Mon, 8 Sep 2025 09:49:02 -0300
Subject: [PATCH] btrfs: avoid potential out-of-bounds in btrfs_encode_fh()
The function btrfs_encode_fh() does not properly account for the three
cases it handles.
Before writing to the file handle (fh), the function only returns to the
user BTRFS_FID_SIZE_NON_CONNECTABLE (5 dwords, 20 bytes) or
BTRFS_FID_SIZE_CONNECTABLE (8 dwords, 32 bytes).
However, when a parent exists and the root ID of the parent and the
inode are different, the function writes BTRFS_FID_SIZE_CONNECTABLE_ROOT
(10 dwords, 40 bytes).
If *max_len is not large enough, this write goes out of bounds because
BTRFS_FID_SIZE_CONNECTABLE_ROOT is greater than
BTRFS_FID_SIZE_CONNECTABLE originally returned.
This results in an 8-byte out-of-bounds write at
fid->parent_root_objectid = parent_root_id.
A previous attempt to fix this issue was made but was lost.
https://lore.kernel.org/all/4CADAEEC020000780001B32C@vpn.id2.novell.com/
Although this issue does not seem to be easily triggerable, it is a
potential memory corruption bug that should be fixed. This patch
resolves the issue by ensuring the function returns the appropriate size
for all three cases and validates that *max_len is large enough before
writing any data.
Fixes: be6e8dc0ba84 ("NFS support for btrfs - v3")
CC: stable(a)vger.kernel.org # 3.0+
Signed-off-by: Anderson Nascimento <anderson(a)allelesecurity.com>
Reviewed-by: David Sterba <dsterba(a)suse.com>
Signed-off-by: David Sterba <dsterba(a)suse.com>
diff --git a/fs/btrfs/export.c b/fs/btrfs/export.c
index d062ac521051..230d9326b685 100644
--- a/fs/btrfs/export.c
+++ b/fs/btrfs/export.c
@@ -23,7 +23,11 @@ static int btrfs_encode_fh(struct inode *inode, u32 *fh, int *max_len,
int type;
if (parent && (len < BTRFS_FID_SIZE_CONNECTABLE)) {
- *max_len = BTRFS_FID_SIZE_CONNECTABLE;
+ if (btrfs_root_id(BTRFS_I(inode)->root) !=
+ btrfs_root_id(BTRFS_I(parent)->root))
+ *max_len = BTRFS_FID_SIZE_CONNECTABLE_ROOT;
+ else
+ *max_len = BTRFS_FID_SIZE_CONNECTABLE;
return FILEID_INVALID;
} else if (len < BTRFS_FID_SIZE_NON_CONNECTABLE) {
*max_len = BTRFS_FID_SIZE_NON_CONNECTABLE;
@@ -45,6 +49,8 @@ static int btrfs_encode_fh(struct inode *inode, u32 *fh, int *max_len,
parent_root_id = btrfs_root_id(BTRFS_I(parent)->root);
if (parent_root_id != fid->root_objectid) {
+ if (*max_len < BTRFS_FID_SIZE_CONNECTABLE_ROOT)
+ return FILEID_INVALID;
fid->parent_root_objectid = parent_root_id;
len = BTRFS_FID_SIZE_CONNECTABLE_ROOT;
type = FILEID_BTRFS_WITH_PARENT_ROOT;