From: Bruce Ashfield <[email protected]>
Integrating the following commit(s) to linux-yocto-rt/6.1:
1/17 [
Author: Tvrtko Ursulin
Email: [email protected]
Subject: drm/i915: Do not disable preemption for resets
Date: Fri, 18 Aug 2023 22:45:25 -0400
[commit 40cd2835ced288789a685aa4aa7bc04b492dcd45 in linux-rt-devel]
Commit ade8a0f59844 ("drm/i915: Make all GPU resets atomic") added a
preempt disable section over the hardware reset callback to prepare the
driver for being able to reset from atomic contexts.
In retrospect I can see that the work item at a time was about removing
the struct mutex from the reset path. Code base also briefly entertained
the idea of doing the reset under stop_machine in order to serialize
userspace mmap and temporary glitch in the fence registers (see
eb8d0f5af4ec ("drm/i915: Remove GPU reset dependence on struct_mutex"),
but that never materialized and was soon removed in 2caffbf11762
("drm/i915: Revoke mmaps and prevent access to fence registers across
reset") and replaced with a SRCU based solution.
As such, as far as I can see, today we still have a requirement that
resets must not sleep (invoked from submission tasklets), but no need to
support invoking them from a truly atomic context.
Given that the preemption section is problematic on RT kernels, since the
uncore lock becomes a sleeping lock and so is invalid in such section,
lets try and remove it. Potential downside is that our short waits on GPU
to complete the reset may get extended if CPU scheduling interferes, but
in practice that probably isn't a deal breaker.
In terms of mechanics, since the preemption disabled block is being
removed we just need to replace a few of the wait_for_atomic macros into
busy looping versions which will work (and not complain) when called from
non-atomic sections.
Signed-off-by: Tvrtko Ursulin <[email protected]>
Cc: Chris Wilson <[email protected]>
Cc: Paul Gortmaker <[email protected]>
Cc: Sebastian Andrzej Siewior <[email protected]>
Acked-by: Sebastian Andrzej Siewior <[email protected]>
Link:
https://lore.kernel.org/r/[email protected]
Signed-off-by: Sebastian Andrzej Siewior <[email protected]>
[PG: backport from v6.4-rt ; minor context fixup caused by b7d70b8b06ed]
Signed-off-by: Paul Gortmaker <[email protected]>
Signed-off-by: Clark Williams <[email protected]>
Signed-off-by: Bruce Ashfield <[email protected]>
]
2/17 [
Author: Clark Williams
Email: [email protected]
Subject: 'Linux 6.1.33-rt11'
Date: Mon, 12 Jun 2023 10:40:02 -0500
Signed-off-by: Clark Williams <[email protected]>
Signed-off-by: Bruce Ashfield <[email protected]>
]
5/17 [
Author: Sebastian Andrzej Siewior
Email: [email protected]
Subject: io-mapping: don't disable preempt on RT in
io_mapping_map_atomic_wc().
Date: Fri, 10 Mar 2023 17:29:05 +0100
io_mapping_map_atomic_wc() disables preemption and pagefaults for
historical reasons. The conversion to io_mapping_map_local_wc(), which
only disables migration, cannot be done wholesale because quite some call
sites need to be updated to accommodate with the changed semantics.
On PREEMPT_RT enabled kernels the io_mapping_map_atomic_wc() semantics are
problematic due to the implicit disabling of preemption which makes it
impossible to acquire 'sleeping' spinlocks within the mapped atomic
sections.
PREEMPT_RT replaces the preempt_disable() with a migrate_disable() for
more than a decade. It could be argued that this is a justification to do
this unconditionally, but PREEMPT_RT covers only a limited number of
architectures and it disables some functionality which limits the coverage
further.
Limit the replacement to PREEMPT_RT for now. This is also done
kmap_atomic().
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Sebastian Andrzej Siewior <[email protected]>
Reported-by: Richard Weinberger <[email protected]>
Link:
https://lore.kernel.org/caflxgvw0wmxamqyqj5wgvvsbkhq2d2xcxtogmcpgq9ndc-m...@mail.gmail.com
Cc: Thomas Gleixner <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
(cherry picked from commit 7eb16f23b9a415f062db22739e59bb144e0b24ab)
Signed-off-by: Clark Williams <[email protected]>
Signed-off-by: Bruce Ashfield <[email protected]>
]
6/17 [
Author: Sebastian Andrzej Siewior
Email: [email protected]
Subject: locking/rwbase: Mitigate indefinite writer starvation
Date: Tue, 21 Mar 2023 17:11:40 +0100
On PREEMPT_RT, rw_semaphore and rwlock_t locks are unfair to writers.
Readers can indefinitely acquire the lock unless the writer fully acquired
the lock, which might never happen if there is always a reader in the
critical section owning the lock.
Mel Gorman reported that since LTP-20220121 the dio_truncate test case
went from having 1 reader to having 16 readers and that number of readers
is sufficient to prevent the down_write ever succeeding while readers
exist. Eventually the test is killed after 30 minutes as a failure.
Mel proposed a timeout to limit how long a writer can be blocked until
the reader is forced into the slowpath.
Thomas argued that there is no added value by providing this timeout. From
a PREEMPT_RT point of view, there are no critical rw_semaphore or rwlock_t
locks left where the reader must be preferred.
Mitigate indefinite writer starvation by forcing the READER into the
slowpath once the WRITER attempts to acquire the lock.
Reported-by: Mel Gorman <[email protected]>
Signed-off-by: Sebastian Andrzej Siewior <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
Acked-by: Mel Gorman <[email protected]>
Link: https://lore.kernel.org/877cwbq4cq.ffs@tglx
Link: https://lore.kernel.org/r/[email protected]
Cc: Linus Torvalds <[email protected]>
(cherry picked from commit 286deb7ec03d941664ac3ffaff58814b454adf65)
Signed-off-by: Clark Williams <[email protected]>
Signed-off-by: Bruce Ashfield <[email protected]>
]
7/17 [
Author: Paolo Abeni
Email: [email protected]
Subject: revert: "softirq: Let ksoftirqd do its job"
Date: Mon, 8 May 2023 08:17:44 +0200
Due to the mentioned commit, when the ksoftirqd processes take charge
of softirq processing, the system can experience high latencies.
In the past a few workarounds have been implemented for specific
side-effects of the above:
commit 1ff688209e2e ("watchdog: core: make sure the watchdog_worker is not
deferred")
commit 8d5755b3f77b ("watchdog: softdog: fire watchdog even if softirqs do
not get to run")
commit 217f69743681 ("net: busy-poll: allow preemption in sk_busy_loop()")
commit 3c53776e29f8 ("Mark HI and TASKLET softirq synchronous")
but the latency problem still exists in real-life workloads, see the
link below.
The reverted commit intended to solve a live-lock scenario that can now
be addressed with the NAPI threaded mode, introduced with commit
29863d41bb6e ("net: implement threaded-able napi poll loop support"),
and nowadays in a pretty stable status.
While a complete solution to put softirq processing under nice resource
control would be preferable, that has proven to be a very hard task. In
the short term, remove the main pain point, and also simplify a bit the
current softirq implementation.
Note that this change also reverts commit 3c53776e29f8 ("Mark HI and
TASKLET softirq synchronous") and commit 1342d8080f61 ("softirq: Don't
skip softirq execution when softirq thread is parking"), which are
direct follow-ups of the feature commit. A single change is preferred to
avoid known bad intermediate states introduced by a patch series
reverting them individually.
Link:
https://lore.kernel.org/netdev/[email protected]/
Signed-off-by: Paolo Abeni <[email protected]>
Tested-by: Jason Xing <[email protected]>
Reviewed-by: Jakub Kicinski <[email protected]>
Reviewed-by: Eric Dumazet <[email protected]>
Reviewed-by: Sebastian Andrzej Siewior <[email protected]>
Link:
https://lore.kernel.org/r/57e66b364f1b6f09c9bc0316742c3b14f4ce83bd.1683526542.git.pab...@redhat.com
Signed-off-by: Sebastian Andrzej Siewior <[email protected]>
(cherry picked from commit b8a04a538ed4755dc97c403ee3b8dd882955c98c)
Signed-off-by: Clark Williams <[email protected]>
Signed-off-by: Bruce Ashfield <[email protected]>
]
8/17 [
Author: Peter Zijlstra
Email: [email protected]
Subject: debugobjects,locking: Annotate debug_object_fill_pool() wait type
violation
Date: Tue, 25 Apr 2023 17:03:13 +0200
There is an explicit wait-type violation in debug_object_fill_pool()
for PREEMPT_RT=n kernels which allows them to more easily fill the
object pool and reduce the chance of allocation failures.
Lockdep's wait-type checks are designed to check the PREEMPT_RT
locking rules even for PREEMPT_RT=n kernels and object to this, so
create a lockdep annotation to allow this to stand.
Specifically, create a 'lock' type that overrides the inner wait-type
while it is held -- allowing one to temporarily raise it, such that
the violation is hidden.
Reported-by: Vlastimil Babka <[email protected]>
Reported-by: Qi Zheng <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Tested-by: Qi Zheng <[email protected]>
Link:
https://lkml.kernel.org/r/[email protected]
(cherry picked from commit 0cce06ba859a515bd06224085d3addb870608b6d)
Signed-off-by: Clark Williams <[email protected]>
Signed-off-by: Bruce Ashfield <[email protected]>
]
9/17 [
Author: Wander Lairson Costa
Email: [email protected]
Subject: sched: avoid false lockdep splat in put_task_struct()
Date: Wed, 14 Jun 2023 09:23:22 -0300
In put_task_struct(), a spin_lock is indirectly acquired under the kernel
stock. When running the kernel in real-time (RT) configuration, the
operation is dispatched to a preemptible context call to ensure
guaranteed preemption. However, if PROVE_RAW_LOCK_NESTING is enabled
and __put_task_struct() is called while holding a raw_spinlock, lockdep
incorrectly reports an "Invalid lock context" in the stock kernel.
This false splat occurs because lockdep is unaware of the different
route taken under RT. To address this issue, override the inner wait
type to prevent the false lockdep splat.
Signed-off-by: Wander Lairson Costa <[email protected]>
Suggested-by: Oleg Nesterov <[email protected]>
Suggested-by: Sebastian Andrzej Siewior <[email protected]>
Suggested-by: Peter Zijlstra <[email protected]>
Cc: Steven Rostedt <[email protected]>
Cc: Luis Goncalves <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Sebastian Andrzej Siewior <[email protected]>
(cherry picked from commit a5e446e728e89d5f5c5e427cc919bc7813c64c28)
Signed-off-by: Clark Williams <[email protected]>
Signed-off-by: Bruce Ashfield <[email protected]>
]
10/17 [
Author: Sebastian Andrzej Siewior
Email: [email protected]
Subject: mm/page_alloc: Use write_seqlock_irqsave() instead write_seqlock()
+ local_irq_save().
Date: Fri, 23 Jun 2023 22:15:17 +0200
__build_all_zonelists() acquires zonelist_update_seq by first disabling
interrupts via local_irq_save() and then acquiring the seqlock with
write_seqlock(). This is troublesome and leads to problems on
PREEMPT_RT. The problem is that the inner spinlock_t becomes a sleeping
lock on PREEMPT_RT and must not be acquired with disabled interrupts.
The API provides write_seqlock_irqsave() which does the right thing in
one step.
printk_deferred_enter() has to be invoked in non-migrate-able context to
ensure that deferred printing is enabled and disabled on the same CPU.
This is the case after zonelist_update_seq has been acquired.
There was discussion on the first submission that the order should be:
local_irq_disable();
printk_deferred_enter();
write_seqlock();
to avoid pitfalls like having an unaccounted printk() coming from
write_seqlock_irqsave() before printk_deferred_enter() is invoked. The
only origin of such a printk() can be a lockdep splat because the
lockdep annotation happens after the sequence count is incremented.
This is exceptional and subject to change.
It was also pointed that PREEMPT_RT can be affected by the printk
problem since its write_seqlock_irqsave() does not really disable
interrupts. This isn't the case because PREEMPT_RT's printk
implementation differs from the mainline implementation in two important
aspects:
- Printing happens in a dedicated threads and not at during the
invocation of printk().
- In emergency cases where synchronous printing is used, a different
driver is used which does not use tty_port::lock.
Acquire zonelist_update_seq with write_seqlock_irqsave() and then defer
printk output.
Fixes: 1007843a91909 ("mm/page_alloc: fix potential deadlock on
zonelist_update_seq seqlock")
Acked-by: Michal Hocko <[email protected]>
Reviewed-by: David Hildenbrand <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Sebastian Andrzej Siewior <[email protected]>
(cherry picked from commit 4d1139baae8bc4fff3728d1d204bdb04c13dbe10)
Signed-off-by: Clark Williams <[email protected]>
Signed-off-by: Bruce Ashfield <[email protected]>
]
11/17 [
Author: Sebastian Andrzej Siewior
Email: [email protected]
Subject: bpf: Remove in_atomic() from bpf_link_put().
Date: Wed, 14 Jun 2023 10:34:30 +0200
bpf_free_inode() is invoked as a RCU callback. Usually RCU callbacks are
invoked within softirq context. By setting rcutree.use_softirq=0 boot
option the RCU callbacks will be invoked in a per-CPU kthread with
bottom halves disabled which implies a RCU read section.
On PREEMPT_RT the context remains fully preemptible. The RCU read
section however does not allow schedule() invocation. The latter happens
in mutex_lock() performed by bpf_trampoline_unlink_prog() originated
from bpf_link_put().
It was pointed out that the bpf_link_put() invocation should not be
delayed if originated from close(). It was also pointed out that other
invocations from within a syscall should also avoid the workqueue.
Everyone else should use workqueue by default to remain safe in the
future (while auditing the code, every caller was preemptible except for
the RCU case).
Let bpf_link_put() use the worker unconditionally. Add
bpf_link_put_direct() which will directly free the resources and is used
by close() and from within __sys_bpf().
Signed-off-by: Sebastian Andrzej Siewior <[email protected]>
Signed-off-by: Andrii Nakryiko <[email protected]>
Link: https://lore.kernel.org/bpf/[email protected]
(cherry picked from commit ab5d47bd41b1db82c295b0e751e2b822b43a4b5a)
Signed-off-by: Clark Williams <[email protected]>
Signed-off-by: Bruce Ashfield <[email protected]>
]
12/17 [
Author: Thomas Gleixner
Email: [email protected]
Subject: posix-timers: Ensure timer ID search-loop limit is valid
Date: Thu, 1 Jun 2023 20:58:47 +0200
posix_timer_add() tries to allocate a posix timer ID by starting from the
cached ID which was stored by the last successful allocation.
This is done in a loop searching the ID space for a free slot one by
one. The loop has to terminate when the search wrapped around to the
starting point.
But that's racy vs. establishing the starting point. That is read out
lockless, which leads to the following problem:
CPU0 CPU1
posix_timer_add()
start = sig->posix_timer_id;
lock(hash_lock);
... posix_timer_add()
if (++sig->posix_timer_id < 0)
start = sig->posix_timer_id;
sig->posix_timer_id = 0;
So CPU1 can observe a negative start value, i.e. -1, and the loop break
never happens because the condition can never be true:
if (sig->posix_timer_id == start)
break;
While this is unlikely to ever turn into an endless loop as the ID space is
huge (INT_MAX), the racy read of the start value caught the attention of
KCSAN and Dmitry unearthed that incorrectness.
Rewrite it so that all id operations are under the hash lock.
Reported-by: [email protected]
Reported-by: Dmitry Vyukov <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Reviewed-by: Frederic Weisbecker <[email protected]>
Link: https://lore.kernel.org/r/87bkhzdn6g.ffs@tglx
(cherry picked from commit 8ce8849dd1e78dadcee0ec9acbd259d239b7069f)
Signed-off-by: Clark Williams <[email protected]>
Signed-off-by: Bruce Ashfield <[email protected]>
]
Signed-off-by: Bruce Ashfield <[email protected]>
Signed-off-by: Alexandre Belloni <[email protected]>
Signed-off-by: Richard Purdie <[email protected]>
(cherry picked from commit 53e612c42ce438b100505c93d8bb65e59f49895d)
Signed-off-by: Steve Sakoman <[email protected]>
---
meta/recipes-kernel/linux/linux-yocto-rt_6.1.bb | 4 ++--
meta/recipes-kernel/linux/linux-yocto-tiny_6.1.bb | 2 +-
meta/recipes-kernel/linux/linux-yocto_6.1.bb | 2 +-
3 files changed, 4 insertions(+), 4 deletions(-)
diff --git a/meta/recipes-kernel/linux/linux-yocto-rt_6.1.bb
b/meta/recipes-kernel/linux/linux-yocto-rt_6.1.bb
index 8d07058b71..78e7dd4d13 100644
--- a/meta/recipes-kernel/linux/linux-yocto-rt_6.1.bb
+++ b/meta/recipes-kernel/linux/linux-yocto-rt_6.1.bb
@@ -14,8 +14,8 @@ python () {
raise bb.parse.SkipRecipe("Set PREFERRED_PROVIDER_virtual/kernel to
linux-yocto-rt to enable it")
}
-SRCREV_machine ?= "2fc300ad2664d72a382351afaa02208e3bcec857"
-SRCREV_meta ?= "5f331d55d0900030f5bc9b139c815f3f01a8ffd4"
+SRCREV_machine ?= "4c0acd6ff800dc4d1630b11640984343bffe7825"
+SRCREV_meta ?= "c5b4dd4dc469548ca1f7129c5c131f8d6cf5ff94"
SRC_URI =
"git://git.yoctoproject.org/linux-yocto.git;branch=${KBRANCH};name=machine;protocol=https
\
git://git.yoctoproject.org/yocto-kernel-cache;type=kmeta;name=meta;branch=yocto-6.1;destsuffix=${KMETA};protocol=https"
diff --git a/meta/recipes-kernel/linux/linux-yocto-tiny_6.1.bb
b/meta/recipes-kernel/linux/linux-yocto-tiny_6.1.bb
index c0871532df..d91ed65999 100644
--- a/meta/recipes-kernel/linux/linux-yocto-tiny_6.1.bb
+++ b/meta/recipes-kernel/linux/linux-yocto-tiny_6.1.bb
@@ -18,7 +18,7 @@ KMETA = "kernel-meta"
KCONF_BSP_AUDIT_LEVEL = "2"
SRCREV_machine ?= "e083231c43f3773e5ca1f6d46411e1fda1081a6e"
-SRCREV_meta ?= "5f331d55d0900030f5bc9b139c815f3f01a8ffd4"
+SRCREV_meta ?= "c5b4dd4dc469548ca1f7129c5c131f8d6cf5ff94"
PV = "${LINUX_VERSION}+git"
diff --git a/meta/recipes-kernel/linux/linux-yocto_6.1.bb
b/meta/recipes-kernel/linux/linux-yocto_6.1.bb
index 6564731da9..f431e4a937 100644
--- a/meta/recipes-kernel/linux/linux-yocto_6.1.bb
+++ b/meta/recipes-kernel/linux/linux-yocto_6.1.bb
@@ -29,7 +29,7 @@ SRCREV_machine:qemux86 ?=
"e083231c43f3773e5ca1f6d46411e1fda1081a6e"
SRCREV_machine:qemux86-64 ?= "e083231c43f3773e5ca1f6d46411e1fda1081a6e"
SRCREV_machine:qemumips64 ?= "a5de8564807b47662da3670c5b358a1494faef77"
SRCREV_machine ?= "e083231c43f3773e5ca1f6d46411e1fda1081a6e"
-SRCREV_meta ?= "5f331d55d0900030f5bc9b139c815f3f01a8ffd4"
+SRCREV_meta ?= "c5b4dd4dc469548ca1f7129c5c131f8d6cf5ff94"
# set your preferred provider of linux-yocto to 'linux-yocto-upstream', and
you'll
# get the <version>/base branch, which is pure upstream -stable, and the same
--
2.34.1
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