This code is used only when CONFIG_PREEMPT=n and only in non-atomic context:
xen_in_preemptible_hcall is set only in privcmd_ioctl_hypercall().
Thus preempt_count is zero and should_resched() is equal to need_resched().
Signed-off-by: Konstantin Khlebnikov <[email protected]>
---
drivers/xen/preempt.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/xen/preempt.c b/drivers/xen/preempt.c
index a1800c150839..08cb419eb4e6 100644
--- a/drivers/xen/preempt.c
+++ b/drivers/xen/preempt.c
@@ -31,7 +31,7 @@ EXPORT_SYMBOL_GPL(xen_in_preemptible_hcall);
asmlinkage __visible void xen_maybe_preempt_hcall(void)
{
if (unlikely(__this_cpu_read(xen_in_preemptible_hcall)
- && should_resched())) {
+ && need_resched())) {
/*
* Clear flag as we may be rescheduled on a different
* cpu.
Function should_resched() is equal to (!preempt_count() && need_resched()).
In preemptive kernel preempt_count here is non-zero because of vc->lock.
Signed-off-by: Konstantin Khlebnikov <[email protected]>
---
arch/powerpc/kvm/book3s_hv.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index 68d067ad4222..a9f753fb73a8 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -2178,7 +2178,7 @@ static int kvmppc_run_vcpu(struct kvm_run *kvm_run, struct kvm_vcpu *vcpu)
vc->runner = vcpu;
if (n_ceded == vc->n_runnable) {
kvmppc_vcore_blocked(vc);
- } else if (should_resched()) {
+ } else if (need_resched()) {
vc->vcore_state = VCORE_PREEMPT;
/* Let something else run */
cond_resched_lock(&vc->lock);
These functions check should_resched() before unlocking spinlock/bh-enable:
preempt_count always non-zero => should_resched() always returns false.
cond_resched_lock() worked iff spin_needbreak is set.
This patch adds argument "preempt_offset" to should_resched().
preempt_count offset constants for that:
PREEMPT_DISABLE_OFFSET - offset after preempt_disable()
PREEMPT_LOCK_OFFSET - offset after spin_lock()
SOFTIRQ_DISABLE_OFFSET - offset after local_bh_distable()
SOFTIRQ_LOCK_OFFSET - offset after spin_lock_bh()
Signed-off-by: Konstantin Khlebnikov <[email protected]>
---
arch/x86/include/asm/preempt.h | 4 ++--
include/asm-generic/preempt.h | 5 +++--
include/linux/preempt.h | 19 ++++++++++++++-----
include/linux/sched.h | 6 ------
kernel/sched/core.c | 6 +++---
5 files changed, 22 insertions(+), 18 deletions(-)
diff --git a/arch/x86/include/asm/preempt.h b/arch/x86/include/asm/preempt.h
index dca71714f860..b12f81022a6b 100644
--- a/arch/x86/include/asm/preempt.h
+++ b/arch/x86/include/asm/preempt.h
@@ -90,9 +90,9 @@ static __always_inline bool __preempt_count_dec_and_test(void)
/*
* Returns true when we need to resched and can (barring IRQ state).
*/
-static __always_inline bool should_resched(void)
+static __always_inline bool should_resched(int preempt_offset)
{
- return unlikely(!raw_cpu_read_4(__preempt_count));
+ return unlikely(raw_cpu_read_4(__preempt_count) == preempt_offset);
}
#ifdef CONFIG_PREEMPT
diff --git a/include/asm-generic/preempt.h b/include/asm-generic/preempt.h
index d0a7a4753db2..0bec580a4885 100644
--- a/include/asm-generic/preempt.h
+++ b/include/asm-generic/preempt.h
@@ -71,9 +71,10 @@ static __always_inline bool __preempt_count_dec_and_test(void)
/*
* Returns true when we need to resched and can (barring IRQ state).
*/
-static __always_inline bool should_resched(void)
+static __always_inline bool should_resched(int preempt_offset)
{
- return unlikely(!preempt_count() && tif_need_resched());
+ return unlikely(preempt_count() == preempt_offset &&
+ tif_need_resched());
}
#ifdef CONFIG_PREEMPT
diff --git a/include/linux/preempt.h b/include/linux/preempt.h
index 84991f185173..bea8dd8ff5e0 100644
--- a/include/linux/preempt.h
+++ b/include/linux/preempt.h
@@ -84,13 +84,21 @@
*/
#define in_nmi() (preempt_count() & NMI_MASK)
+/*
+ * The preempt_count offset after preempt_disable();
+ */
#if defined(CONFIG_PREEMPT_COUNT)
-# define PREEMPT_DISABLE_OFFSET 1
+# define PREEMPT_DISABLE_OFFSET PREEMPT_OFFSET
#else
-# define PREEMPT_DISABLE_OFFSET 0
+# define PREEMPT_DISABLE_OFFSET 0
#endif
/*
+ * The preempt_count offset after spin_lock()
+ */
+#define PREEMPT_LOCK_OFFSET PREEMPT_DISABLE_OFFSET
+
+/*
* The preempt_count offset needed for things like:
*
* spin_lock_bh()
@@ -103,7 +111,7 @@
*
* Work as expected.
*/
-#define SOFTIRQ_LOCK_OFFSET (SOFTIRQ_DISABLE_OFFSET + PREEMPT_DISABLE_OFFSET)
+#define SOFTIRQ_LOCK_OFFSET (SOFTIRQ_DISABLE_OFFSET + PREEMPT_LOCK_OFFSET)
/*
* Are we running in atomic context? WARNING: this macro cannot
@@ -124,7 +132,8 @@
#if defined(CONFIG_DEBUG_PREEMPT) || defined(CONFIG_PREEMPT_TRACER)
extern void preempt_count_add(int val);
extern void preempt_count_sub(int val);
-#define preempt_count_dec_and_test() ({ preempt_count_sub(1); should_resched(); })
+#define preempt_count_dec_and_test() \
+ ({ preempt_count_sub(1); should_resched(0); })
#else
#define preempt_count_add(val) __preempt_count_add(val)
#define preempt_count_sub(val) __preempt_count_sub(val)
@@ -184,7 +193,7 @@ do { \
#define preempt_check_resched() \
do { \
- if (should_resched()) \
+ if (should_resched(0)) \
__preempt_schedule(); \
} while (0)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index ae21f1591615..a8e9b17acdee 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -2885,12 +2885,6 @@ extern int _cond_resched(void);
extern int __cond_resched_lock(spinlock_t *lock);
-#ifdef CONFIG_PREEMPT_COUNT
-#define PREEMPT_LOCK_OFFSET PREEMPT_OFFSET
-#else
-#define PREEMPT_LOCK_OFFSET 0
-#endif
-
#define cond_resched_lock(lock) ({ \
___might_sleep(__FILE__, __LINE__, PREEMPT_LOCK_OFFSET);\
__cond_resched_lock(lock); \
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 78b4bad10081..d9a4d93dc879 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4492,7 +4492,7 @@ SYSCALL_DEFINE0(sched_yield)
int __sched _cond_resched(void)
{
- if (should_resched()) {
+ if (should_resched(0)) {
preempt_schedule_common();
return 1;
}
@@ -4510,7 +4510,7 @@ EXPORT_SYMBOL(_cond_resched);
*/
int __cond_resched_lock(spinlock_t *lock)
{
- int resched = should_resched();
+ int resched = should_resched(PREEMPT_LOCK_OFFSET);
int ret = 0;
lockdep_assert_held(lock);
@@ -4532,7 +4532,7 @@ int __sched __cond_resched_softirq(void)
{
BUG_ON(!in_softirq());
- if (should_resched()) {
+ if (should_resched(SOFTIRQ_DISABLE_OFFSET)) {
local_bh_enable();
preempt_schedule_common();
local_bh_disable();
On Wed, 2015-07-15 at 12:52 +0300, Konstantin Khlebnikov wrote:
> These functions check should_resched() before unlocking spinlock/bh-enable:
> preempt_count always non-zero => should_resched() always returns false.
> cond_resched_lock() worked iff spin_needbreak is set.
Interesting, this definitely used to work (linux-3.11)
Any idea of which commit broke things ?
On 15.07.2015 15:16, Eric Dumazet wrote:
> On Wed, 2015-07-15 at 12:52 +0300, Konstantin Khlebnikov wrote:
>> These functions check should_resched() before unlocking spinlock/bh-enable:
>> preempt_count always non-zero => should_resched() always returns false.
>> cond_resched_lock() worked iff spin_needbreak is set.
>
> Interesting, this definitely used to work (linux-3.11)
>
> Any idea of which commit broke things ?
>
Searching... done
This one: bdb43806589096ac4272fe1307e789846ac08d7c in v3.13
before
-static inline int should_resched(void)
-{
- return need_resched() && !(preempt_count() & PREEMPT_ACTIVE);
-}
after
+static __always_inline bool should_resched(void)
+{
+ return unlikely(!*preempt_count_ptr());
+}
So,
Fixes: bdb438065890 ("sched: Extract the basic add/sub preempt_count
modifiers")
--
Konstantin
On Wed, Jul 15, 2015 at 03:52:34PM +0300, Konstantin Khlebnikov wrote:
> On 15.07.2015 15:16, Eric Dumazet wrote:
> >On Wed, 2015-07-15 at 12:52 +0300, Konstantin Khlebnikov wrote:
> >>These functions check should_resched() before unlocking spinlock/bh-enable:
> >>preempt_count always non-zero => should_resched() always returns false.
> >>cond_resched_lock() worked iff spin_needbreak is set.
> >
> >Interesting, this definitely used to work (linux-3.11)
> >
> >Any idea of which commit broke things ?
> >
>
> Searching... done
>
> This one: bdb43806589096ac4272fe1307e789846ac08d7c in v3.13
>
> before
>
> -static inline int should_resched(void)
> -{
> - return need_resched() && !(preempt_count() & PREEMPT_ACTIVE);
> -}
>
> after
>
> +static __always_inline bool should_resched(void)
> +{
> + return unlikely(!*preempt_count_ptr());
> +}
Argh, indeed!
>
> So,
>
> Fixes: bdb438065890 ("sched: Extract the basic add/sub preempt_count
> modifiers")
Thanks!
On 15/07/15 10:52, Konstantin Khlebnikov wrote:
> This code is used only when CONFIG_PREEMPT=n and only in non-atomic context:
> xen_in_preemptible_hcall is set only in privcmd_ioctl_hypercall().
> Thus preempt_count is zero and should_resched() is equal to need_resched().
Applied to for-linus-4.3, thanks.
David
Commit-ID: 0fa2f5cb2b0ecd8d56baa51f35f09aab234eb0bf
Gitweb: http://git.kernel.org/tip/0fa2f5cb2b0ecd8d56baa51f35f09aab234eb0bf
Author: Konstantin Khlebnikov <[email protected]>
AuthorDate: Wed, 15 Jul 2015 12:52:01 +0300
Committer: Ingo Molnar <[email protected]>
CommitDate: Mon, 3 Aug 2015 12:21:23 +0200
sched/preempt, xen: Use need_resched() instead of should_resched()
This code is used only when CONFIG_PREEMPT=n and only in non-atomic context:
xen_in_preemptible_hcall is set only in privcmd_ioctl_hypercall().
Thus preempt_count is zero and should_resched() is equal to need_resched().
Signed-off-by: Konstantin Khlebnikov <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Cc: Alexander Graf <[email protected]>
Cc: Boris Ostrovsky <[email protected]>
Cc: David Vrabel <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Mike Galbraith <[email protected]>
Cc: Paul Mackerras <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Link: http://lkml.kernel.org/r/20150715095201.12246.49283.stgit@buzz
Signed-off-by: Ingo Molnar <[email protected]>
---
drivers/xen/preempt.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/xen/preempt.c b/drivers/xen/preempt.c
index a1800c1..08cb419 100644
--- a/drivers/xen/preempt.c
+++ b/drivers/xen/preempt.c
@@ -31,7 +31,7 @@ EXPORT_SYMBOL_GPL(xen_in_preemptible_hcall);
asmlinkage __visible void xen_maybe_preempt_hcall(void)
{
if (unlikely(__this_cpu_read(xen_in_preemptible_hcall)
- && should_resched())) {
+ && need_resched())) {
/*
* Clear flag as we may be rescheduled on a different
* cpu.
Commit-ID: c56dadf39761a6157239cac39e3988998c994f98
Gitweb: http://git.kernel.org/tip/c56dadf39761a6157239cac39e3988998c994f98
Author: Konstantin Khlebnikov <[email protected]>
AuthorDate: Wed, 15 Jul 2015 12:52:03 +0300
Committer: Ingo Molnar <[email protected]>
CommitDate: Mon, 3 Aug 2015 12:21:24 +0200
sched/preempt, powerpc, kvm: Use need_resched() instead of should_resched()
Function should_resched() is equal to (!preempt_count() && need_resched()).
In preemptive kernel preempt_count here is non-zero because of vc->lock.
Signed-off-by: Konstantin Khlebnikov <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Cc: Alexander Graf <[email protected]>
Cc: Boris Ostrovsky <[email protected]>
Cc: David Vrabel <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Mike Galbraith <[email protected]>
Cc: Paul Mackerras <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Link: http://lkml.kernel.org/r/20150715095203.12246.72922.stgit@buzz
Signed-off-by: Ingo Molnar <[email protected]>
---
arch/powerpc/kvm/book3s_hv.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index 68d067a..a9f753f 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -2178,7 +2178,7 @@ static int kvmppc_run_vcpu(struct kvm_run *kvm_run, struct kvm_vcpu *vcpu)
vc->runner = vcpu;
if (n_ceded == vc->n_runnable) {
kvmppc_vcore_blocked(vc);
- } else if (should_resched()) {
+ } else if (need_resched()) {
vc->vcore_state = VCORE_PREEMPT;
/* Let something else run */
cond_resched_lock(&vc->lock);
Commit-ID: fe32d3cd5e8eb0f82e459763374aa80797023403
Gitweb: http://git.kernel.org/tip/fe32d3cd5e8eb0f82e459763374aa80797023403
Author: Konstantin Khlebnikov <[email protected]>
AuthorDate: Wed, 15 Jul 2015 12:52:04 +0300
Committer: Ingo Molnar <[email protected]>
CommitDate: Mon, 3 Aug 2015 12:21:24 +0200
sched/preempt: Fix cond_resched_lock() and cond_resched_softirq()
These functions check should_resched() before unlocking spinlock/bh-enable:
preempt_count always non-zero => should_resched() always returns false.
cond_resched_lock() worked iff spin_needbreak is set.
This patch adds argument "preempt_offset" to should_resched().
preempt_count offset constants for that:
PREEMPT_DISABLE_OFFSET - offset after preempt_disable()
PREEMPT_LOCK_OFFSET - offset after spin_lock()
SOFTIRQ_DISABLE_OFFSET - offset after local_bh_distable()
SOFTIRQ_LOCK_OFFSET - offset after spin_lock_bh()
Signed-off-by: Konstantin Khlebnikov <[email protected]>
Signed-off-by: Peter Zijlstra (Intel) <[email protected]>
Cc: Alexander Graf <[email protected]>
Cc: Boris Ostrovsky <[email protected]>
Cc: David Vrabel <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Mike Galbraith <[email protected]>
Cc: Paul Mackerras <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Fixes: bdb438065890 ("sched: Extract the basic add/sub preempt_count modifiers")
Link: http://lkml.kernel.org/r/20150715095204.12246.98268.stgit@buzz
Signed-off-by: Ingo Molnar <[email protected]>
---
arch/x86/include/asm/preempt.h | 4 ++--
include/asm-generic/preempt.h | 5 +++--
include/linux/preempt.h | 19 ++++++++++++++-----
include/linux/sched.h | 6 ------
kernel/sched/core.c | 6 +++---
5 files changed, 22 insertions(+), 18 deletions(-)
diff --git a/arch/x86/include/asm/preempt.h b/arch/x86/include/asm/preempt.h
index dca7171..b12f810 100644
--- a/arch/x86/include/asm/preempt.h
+++ b/arch/x86/include/asm/preempt.h
@@ -90,9 +90,9 @@ static __always_inline bool __preempt_count_dec_and_test(void)
/*
* Returns true when we need to resched and can (barring IRQ state).
*/
-static __always_inline bool should_resched(void)
+static __always_inline bool should_resched(int preempt_offset)
{
- return unlikely(!raw_cpu_read_4(__preempt_count));
+ return unlikely(raw_cpu_read_4(__preempt_count) == preempt_offset);
}
#ifdef CONFIG_PREEMPT
diff --git a/include/asm-generic/preempt.h b/include/asm-generic/preempt.h
index d0a7a47..0bec580 100644
--- a/include/asm-generic/preempt.h
+++ b/include/asm-generic/preempt.h
@@ -71,9 +71,10 @@ static __always_inline bool __preempt_count_dec_and_test(void)
/*
* Returns true when we need to resched and can (barring IRQ state).
*/
-static __always_inline bool should_resched(void)
+static __always_inline bool should_resched(int preempt_offset)
{
- return unlikely(!preempt_count() && tif_need_resched());
+ return unlikely(preempt_count() == preempt_offset &&
+ tif_need_resched());
}
#ifdef CONFIG_PREEMPT
diff --git a/include/linux/preempt.h b/include/linux/preempt.h
index 84991f1..bea8dd8 100644
--- a/include/linux/preempt.h
+++ b/include/linux/preempt.h
@@ -84,13 +84,21 @@
*/
#define in_nmi() (preempt_count() & NMI_MASK)
+/*
+ * The preempt_count offset after preempt_disable();
+ */
#if defined(CONFIG_PREEMPT_COUNT)
-# define PREEMPT_DISABLE_OFFSET 1
+# define PREEMPT_DISABLE_OFFSET PREEMPT_OFFSET
#else
-# define PREEMPT_DISABLE_OFFSET 0
+# define PREEMPT_DISABLE_OFFSET 0
#endif
/*
+ * The preempt_count offset after spin_lock()
+ */
+#define PREEMPT_LOCK_OFFSET PREEMPT_DISABLE_OFFSET
+
+/*
* The preempt_count offset needed for things like:
*
* spin_lock_bh()
@@ -103,7 +111,7 @@
*
* Work as expected.
*/
-#define SOFTIRQ_LOCK_OFFSET (SOFTIRQ_DISABLE_OFFSET + PREEMPT_DISABLE_OFFSET)
+#define SOFTIRQ_LOCK_OFFSET (SOFTIRQ_DISABLE_OFFSET + PREEMPT_LOCK_OFFSET)
/*
* Are we running in atomic context? WARNING: this macro cannot
@@ -124,7 +132,8 @@
#if defined(CONFIG_DEBUG_PREEMPT) || defined(CONFIG_PREEMPT_TRACER)
extern void preempt_count_add(int val);
extern void preempt_count_sub(int val);
-#define preempt_count_dec_and_test() ({ preempt_count_sub(1); should_resched(); })
+#define preempt_count_dec_and_test() \
+ ({ preempt_count_sub(1); should_resched(0); })
#else
#define preempt_count_add(val) __preempt_count_add(val)
#define preempt_count_sub(val) __preempt_count_sub(val)
@@ -184,7 +193,7 @@ do { \
#define preempt_check_resched() \
do { \
- if (should_resched()) \
+ if (should_resched(0)) \
__preempt_schedule(); \
} while (0)
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 65a8a86..9c14465 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -2891,12 +2891,6 @@ extern int _cond_resched(void);
extern int __cond_resched_lock(spinlock_t *lock);
-#ifdef CONFIG_PREEMPT_COUNT
-#define PREEMPT_LOCK_OFFSET PREEMPT_OFFSET
-#else
-#define PREEMPT_LOCK_OFFSET 0
-#endif
-
#define cond_resched_lock(lock) ({ \
___might_sleep(__FILE__, __LINE__, PREEMPT_LOCK_OFFSET);\
__cond_resched_lock(lock); \
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index fa5826c..f5fad2b 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4496,7 +4496,7 @@ SYSCALL_DEFINE0(sched_yield)
int __sched _cond_resched(void)
{
- if (should_resched()) {
+ if (should_resched(0)) {
preempt_schedule_common();
return 1;
}
@@ -4514,7 +4514,7 @@ EXPORT_SYMBOL(_cond_resched);
*/
int __cond_resched_lock(spinlock_t *lock)
{
- int resched = should_resched();
+ int resched = should_resched(PREEMPT_LOCK_OFFSET);
int ret = 0;
lockdep_assert_held(lock);
@@ -4536,7 +4536,7 @@ int __sched __cond_resched_softirq(void)
{
BUG_ON(!in_softirq());
- if (should_resched()) {
+ if (should_resched(SOFTIRQ_DISABLE_OFFSET)) {
local_bh_enable();
preempt_schedule_common();
local_bh_disable();