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Subject[GIT PULL] core kernel fixes
Linus,

Please pull the latest core-urgent-for-linus git tree from:

git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git core-urgent-for-linus

# HEAD: ec1e1b6109171d1890a437481c35b2b56d2327b8 objtool: Prevent GCC from merging annotate_unreachable(), take 2

Please note that this pull request is RFC due to the top commit:

ec1e1b610917: objtool: Prevent GCC from merging annotate_unreachable(), take 2

... which is admittedly somewhat of an ad-hoc workaround for something the
compiler should have done - if there's another solution we can try that.

The other changes:

- futex race fixes

- objtool build warning fix

- two watchdog fixes: a crash fix (revert) and a /proc/sys/kernel/watchdog_thresh
handling bug fix.

Thanks,

Ingo

------------------>
Don Zickus (1):
watchdog/hardlockup/perf: Use atomics to track in-use cpu counter

Josh Poimboeuf (2):
objtool: Resync objtool's instruction decoder source code copy with the kernel's latest version
objtool: Prevent GCC from merging annotate_unreachable(), take 2

Peter Zijlstra (1):
futex: Fix more put_pi_state() vs. exit_pi_state_list() races

Thomas Gleixner (1):
watchdog/harclockup/perf: Revert a33d44843d45 ("watchdog/hardlockup/perf: Simplify deferred event destroy")


include/linux/compiler.h | 4 ++--
kernel/futex.c | 23 ++++++++++++++++++++---
kernel/watchdog_hld.c | 15 ++++++++++-----
tools/objtool/arch/x86/insn/gen-insn-attr-x86.awk | 1 +
4 files changed, 33 insertions(+), 10 deletions(-)

diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index fd8697aa4f73..202710420d6d 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -191,13 +191,13 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
asm("%c0:\n\t" \
".pushsection .discard.reachable\n\t" \
".long %c0b - .\n\t" \
- ".popsection\n\t" : : "i" (__LINE__)); \
+ ".popsection\n\t" : : "i" (__COUNTER__)); \
})
#define annotate_unreachable() ({ \
asm("%c0:\n\t" \
".pushsection .discard.unreachable\n\t" \
".long %c0b - .\n\t" \
- ".popsection\n\t" : : "i" (__LINE__)); \
+ ".popsection\n\t" : : "i" (__COUNTER__)); \
})
#define ASM_UNREACHABLE \
"999:\n\t" \
diff --git a/kernel/futex.c b/kernel/futex.c
index 0d638f008bb1..76ed5921117a 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -903,11 +903,27 @@ void exit_pi_state_list(struct task_struct *curr)
*/
raw_spin_lock_irq(&curr->pi_lock);
while (!list_empty(head)) {
-
next = head->next;
pi_state = list_entry(next, struct futex_pi_state, list);
key = pi_state->key;
hb = hash_futex(&key);
+
+ /*
+ * We can race against put_pi_state() removing itself from the
+ * list (a waiter going away). put_pi_state() will first
+ * decrement the reference count and then modify the list, so
+ * its possible to see the list entry but fail this reference
+ * acquire.
+ *
+ * In that case; drop the locks to let put_pi_state() make
+ * progress and retry the loop.
+ */
+ if (!atomic_inc_not_zero(&pi_state->refcount)) {
+ raw_spin_unlock_irq(&curr->pi_lock);
+ cpu_relax();
+ raw_spin_lock_irq(&curr->pi_lock);
+ continue;
+ }
raw_spin_unlock_irq(&curr->pi_lock);

spin_lock(&hb->lock);
@@ -918,8 +934,10 @@ void exit_pi_state_list(struct task_struct *curr)
* task still owns the PI-state:
*/
if (head->next != next) {
+ /* retain curr->pi_lock for the loop invariant */
raw_spin_unlock(&pi_state->pi_mutex.wait_lock);
spin_unlock(&hb->lock);
+ put_pi_state(pi_state);
continue;
}

@@ -927,9 +945,8 @@ void exit_pi_state_list(struct task_struct *curr)
WARN_ON(list_empty(&pi_state->list));
list_del_init(&pi_state->list);
pi_state->owner = NULL;
- raw_spin_unlock(&curr->pi_lock);

- get_pi_state(pi_state);
+ raw_spin_unlock(&curr->pi_lock);
raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
spin_unlock(&hb->lock);

diff --git a/kernel/watchdog_hld.c b/kernel/watchdog_hld.c
index 4583feb66393..e449a23e9d59 100644
--- a/kernel/watchdog_hld.c
+++ b/kernel/watchdog_hld.c
@@ -13,6 +13,7 @@
#define pr_fmt(fmt) "NMI watchdog: " fmt

#include <linux/nmi.h>
+#include <linux/atomic.h>
#include <linux/module.h>
#include <linux/sched/debug.h>

@@ -22,10 +23,11 @@
static DEFINE_PER_CPU(bool, hard_watchdog_warn);
static DEFINE_PER_CPU(bool, watchdog_nmi_touch);
static DEFINE_PER_CPU(struct perf_event *, watchdog_ev);
+static DEFINE_PER_CPU(struct perf_event *, dead_event);
static struct cpumask dead_events_mask;

static unsigned long hardlockup_allcpu_dumped;
-static unsigned int watchdog_cpus;
+static atomic_t watchdog_cpus = ATOMIC_INIT(0);

void arch_touch_nmi_watchdog(void)
{
@@ -189,7 +191,8 @@ void hardlockup_detector_perf_enable(void)
if (hardlockup_detector_event_create())
return;

- if (!watchdog_cpus++)
+ /* use original value for check */
+ if (!atomic_fetch_inc(&watchdog_cpus))
pr_info("Enabled. Permanently consumes one hw-PMU counter.\n");

perf_event_enable(this_cpu_read(watchdog_ev));
@@ -204,8 +207,10 @@ void hardlockup_detector_perf_disable(void)

if (event) {
perf_event_disable(event);
+ this_cpu_write(watchdog_ev, NULL);
+ this_cpu_write(dead_event, event);
cpumask_set_cpu(smp_processor_id(), &dead_events_mask);
- watchdog_cpus--;
+ atomic_dec(&watchdog_cpus);
}
}

@@ -219,7 +224,7 @@ void hardlockup_detector_perf_cleanup(void)
int cpu;

for_each_cpu(cpu, &dead_events_mask) {
- struct perf_event *event = per_cpu(watchdog_ev, cpu);
+ struct perf_event *event = per_cpu(dead_event, cpu);

/*
* Required because for_each_cpu() reports unconditionally
@@ -227,7 +232,7 @@ void hardlockup_detector_perf_cleanup(void)
*/
if (event)
perf_event_release_kernel(event);
- per_cpu(watchdog_ev, cpu) = NULL;
+ per_cpu(dead_event, cpu) = NULL;
}
cpumask_clear(&dead_events_mask);
}
diff --git a/tools/objtool/arch/x86/insn/gen-insn-attr-x86.awk b/tools/objtool/arch/x86/insn/gen-insn-attr-x86.awk
index a3d2c62fd805..b02a36b2c14f 100644
--- a/tools/objtool/arch/x86/insn/gen-insn-attr-x86.awk
+++ b/tools/objtool/arch/x86/insn/gen-insn-attr-x86.awk
@@ -1,4 +1,5 @@
#!/bin/awk -f
+# SPDX-License-Identifier: GPL-2.0
# gen-insn-attr-x86.awk: Instruction attribute table generator
# Written by Masami Hiramatsu <mhiramat@redhat.com>
#
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