* [PATCH 1/4] s390/crypto: Replace cond_resched() with schedule()
2026-07-27 16:24 [PATCH 0/4] s390: Remove or replace cond_resched() calls Heiko Carstens
@ 2026-07-27 16:24 ` Heiko Carstens
2026-07-27 17:05 ` sashiko-bot
2026-07-27 16:24 ` [PATCH 2/4] KVM: s390: Remove cond_resched() calls Heiko Carstens
` (2 subsequent siblings)
3 siblings, 1 reply; 9+ messages in thread
From: Heiko Carstens @ 2026-07-27 16:24 UTC (permalink / raw)
To: Alexander Gordeev, Sven Schnelle, Vasily Gorbik,
Christian Borntraeger, Harald Freudenberger, Holger Dengler,
Vineeth Vijayan, Peter Oberparleiter, Janosch Frank,
Claudio Imbrenda, David Hildenbrand, Peter Zijlstra
Cc: linux-s390, linux-kernel
The comment for all cond_resched() calls in crypto code says that the
process should be scheduled away to avoid instant re-invocation of a
callback. This is not what cond_resched() would do or did.
Replace cond_resched() with a call to schedule() which comes closer, but
it looks more like this code wants an msleep() call.
Note that with [1] cond_resched() is always compiled away and becomes a
no-op.
[1] commit 7dadeaa6e851 ("sched: Further restrict the preemption modes")
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
---
arch/s390/crypto/paes_s390.c | 8 ++++----
arch/s390/crypto/phmac_s390.c | 4 ++--
2 files changed, 6 insertions(+), 6 deletions(-)
diff --git a/arch/s390/crypto/paes_s390.c b/arch/s390/crypto/paes_s390.c
index 8cfe6166c193..d02de945f864 100644
--- a/arch/s390/crypto/paes_s390.c
+++ b/arch/s390/crypto/paes_s390.c
@@ -555,7 +555,7 @@ static int ecb_paes_do_one_request(struct crypto_engine *engine, void *areq)
* To avoid immediately re-invocation of this callback,
* tell the scheduler to voluntarily give up the CPU here.
*/
- cond_resched();
+ schedule();
pr_debug("rescheduling request\n");
return -ENOSPC;
} else if (rc) {
@@ -821,7 +821,7 @@ static int cbc_paes_do_one_request(struct crypto_engine *engine, void *areq)
* To avoid immediately re-invocation of this callback,
* tell the scheduler to voluntarily give up the CPU here.
*/
- cond_resched();
+ schedule();
pr_debug("rescheduling request\n");
return -ENOSPC;
} else if (rc) {
@@ -1129,7 +1129,7 @@ static int ctr_paes_do_one_request(struct crypto_engine *engine, void *areq)
* To avoid immediately re-invocation of this callback,
* tell the scheduler to voluntarily give up the CPU here.
*/
- cond_resched();
+ schedule();
pr_debug("rescheduling request\n");
return -ENOSPC;
} else if (rc) {
@@ -1572,7 +1572,7 @@ static int xts_paes_do_one_request(struct crypto_engine *engine, void *areq)
* To avoid immediately re-invocation of this callback,
* tell the scheduler to voluntarily give up the CPU here.
*/
- cond_resched();
+ schedule();
pr_debug("rescheduling request\n");
return -ENOSPC;
} else if (rc) {
diff --git a/arch/s390/crypto/phmac_s390.c b/arch/s390/crypto/phmac_s390.c
index 03ca33ffe6cc..bddfdcee6cb3 100644
--- a/arch/s390/crypto/phmac_s390.c
+++ b/arch/s390/crypto/phmac_s390.c
@@ -895,7 +895,7 @@ static int phmac_do_one_request(struct crypto_engine *engine, void *areq)
* tell scheduler to voluntarily give up the CPU here.
*/
pr_debug("rescheduling request\n");
- cond_resched();
+ schedule();
return -ENOSPC;
} else if (rc) {
hwh_advance(hwh, rc);
@@ -916,7 +916,7 @@ static int phmac_do_one_request(struct crypto_engine *engine, void *areq)
* tell scheduler to voluntarily give up the CPU here.
*/
pr_debug("rescheduling request\n");
- cond_resched();
+ schedule();
return -ENOSPC;
}
break;
--
2.53.0
^ permalink raw reply related [flat|nested] 9+ messages in thread* [PATCH 2/4] KVM: s390: Remove cond_resched() calls
2026-07-27 16:24 [PATCH 0/4] s390: Remove or replace cond_resched() calls Heiko Carstens
2026-07-27 16:24 ` [PATCH 1/4] s390/crypto: Replace cond_resched() with schedule() Heiko Carstens
@ 2026-07-27 16:24 ` Heiko Carstens
2026-07-27 16:57 ` sashiko-bot
2026-07-27 16:24 ` [PATCH 3/4] " Heiko Carstens
2026-07-27 16:24 ` [PATCH 4/4] s390/cio: " Heiko Carstens
3 siblings, 1 reply; 9+ messages in thread
From: Heiko Carstens @ 2026-07-27 16:24 UTC (permalink / raw)
To: Alexander Gordeev, Sven Schnelle, Vasily Gorbik,
Christian Borntraeger, Harald Freudenberger, Holger Dengler,
Vineeth Vijayan, Peter Oberparleiter, Janosch Frank,
Claudio Imbrenda, David Hildenbrand, Peter Zijlstra
Cc: linux-s390, linux-kernel
Since [1] cond_resched() is a no-op on s390. Remove all calls.
[1] commit 7dadeaa6e851 ("sched: Further restrict the preemption modes")
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
---
arch/s390/include/asm/uv.h | 1 -
arch/s390/kvm/gaccess.c | 8 ++------
arch/s390/kvm/gmap.c | 4 ----
arch/s390/kvm/kvm-s390.c | 1 -
arch/s390/kvm/pv.c | 1 -
arch/s390/kvm/vsie.c | 1 -
arch/s390/mm/gmap_helpers.c | 1 -
7 files changed, 2 insertions(+), 15 deletions(-)
diff --git a/arch/s390/include/asm/uv.h b/arch/s390/include/asm/uv.h
index d919e69662f5..795da130342a 100644
--- a/arch/s390/include/asm/uv.h
+++ b/arch/s390/include/asm/uv.h
@@ -461,7 +461,6 @@ static inline int uv_call_sched(unsigned long r1, unsigned long r2)
do {
cc = __uv_call(r1, r2);
- cond_resched();
} while (cc > 1);
return cc;
}
diff --git a/arch/s390/kvm/gaccess.c b/arch/s390/kvm/gaccess.c
index 36102b2727fb..0d389a302a70 100644
--- a/arch/s390/kvm/gaccess.c
+++ b/arch/s390/kvm/gaccess.c
@@ -151,10 +151,8 @@ static void ipte_lock_simple(struct kvm *kvm)
ic = &kvm->arch.sca->ipte_control;
old = READ_ONCE(*ic);
do {
- if (old.k) {
- cond_resched();
+ if (old.k)
goto retry;
- }
new = old;
new.k = 1;
} while (!try_cmpxchg(&ic->val, &old.val, new.val));
@@ -189,10 +187,8 @@ static void ipte_lock_siif(struct kvm *kvm)
ic = &kvm->arch.sca->ipte_control;
old = READ_ONCE(*ic);
do {
- if (old.kg) {
- cond_resched();
+ if (old.kg)
goto retry;
- }
new = old;
new.k = 1;
new.kh++;
diff --git a/arch/s390/kvm/gmap.c b/arch/s390/kvm/gmap.c
index 8abb4f55b306..3758e4009709 100644
--- a/arch/s390/kvm/gmap.c
+++ b/arch/s390/kvm/gmap.c
@@ -941,7 +941,6 @@ void gmap_split_huge_pages(struct gmap *gmap)
scoped_guard(read_lock, &gmap->kvm->mmu_lock)
start = _dat_walk_gfn_range(start, asce_end(gmap->asce), gmap->asce,
&ops, DAT_WALK_IGN_HOLES, gmap);
- cond_resched();
} while (start);
}
@@ -963,7 +962,6 @@ static int _gmap_enable_skeys(struct gmap *gmap)
do {
scoped_guard(write_lock, &gmap->kvm->mmu_lock)
start = dat_reset_skeys(gmap->asce, start);
- cond_resched();
} while (start);
return 0;
}
@@ -1019,7 +1017,6 @@ int gmap_pv_destroy_range(struct gmap *gmap, gfn_t start, gfn_t end, bool interr
DAT_WALK_IGN_HOLES, NULL);
if (interruptible && fatal_signal_pending(current))
return -EINTR;
- cond_resched();
} while (start && start < end);
return 0;
}
@@ -1138,7 +1135,6 @@ void _gmap_set_cmma_all(struct gmap *gmap, bool dirty)
gfn = _dat_walk_gfn_range(gfn, asce_end(gmap->asce), gmap->asce, &ops,
DAT_WALK_IGN_HOLES,
&gmap->kvm->arch.cmma_dirty_pages);
- cond_resched();
} while (gfn);
}
diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index 150b5dd2170e..2ede8f035a38 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -1027,7 +1027,6 @@ static int kvm_s390_set_mem_control(struct kvm *kvm, struct kvm_device_attr *att
do {
scoped_guard(read_lock, &kvm->mmu_lock)
start_gfn = dat_reset_cmma(kvm->arch.gmap->asce, start_gfn);
- cond_resched();
} while (start_gfn);
ret = 0;
break;
diff --git a/arch/s390/kvm/pv.c b/arch/s390/kvm/pv.c
index 1beacc841ca8..935fe308a050 100644
--- a/arch/s390/kvm/pv.c
+++ b/arch/s390/kvm/pv.c
@@ -832,7 +832,6 @@ int kvm_s390_pv_unpack(struct kvm *kvm, unsigned long addr, unsigned long size,
while (offset < size) {
ret = unpack_one(kvm, addr, tweak, offset, rc, rrc);
if (ret == -EAGAIN) {
- cond_resched();
if (fatal_signal_pending(current))
break;
continue;
diff --git a/arch/s390/kvm/vsie.c b/arch/s390/kvm/vsie.c
index eea24562e7db..6dcd3b110c17 100644
--- a/arch/s390/kvm/vsie.c
+++ b/arch/s390/kvm/vsie.c
@@ -1434,7 +1434,6 @@ static int vsie_run(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page)
}
if (sg)
sg = gmap_put(sg);
- cond_resched();
}
if (sg)
sg = gmap_put(sg);
diff --git a/arch/s390/mm/gmap_helpers.c b/arch/s390/mm/gmap_helpers.c
index 4bf7c9012feb..d564cdefb90f 100644
--- a/arch/s390/mm/gmap_helpers.c
+++ b/arch/s390/mm/gmap_helpers.c
@@ -272,7 +272,6 @@ static int __gmap_helper_unshare_zeropages(struct mm_struct *mm)
* truncation. In that case, the shared zeropage would be gone
* and we can simply retry and make progress.
*/
- cond_resched();
goto retry;
}
--
2.53.0
^ permalink raw reply related [flat|nested] 9+ messages in thread* Re: [PATCH 2/4] KVM: s390: Remove cond_resched() calls
2026-07-27 16:24 ` [PATCH 2/4] KVM: s390: Remove cond_resched() calls Heiko Carstens
@ 2026-07-27 16:57 ` sashiko-bot
0 siblings, 0 replies; 9+ messages in thread
From: sashiko-bot @ 2026-07-27 16:57 UTC (permalink / raw)
To: Heiko Carstens
Cc: Vasily Gorbik, linux-s390, Heiko Carstens, Alexander Gordeev
Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
Pre-existing issues:
- [Medium] Missing cpu_relax() in busy-wait loops in ipte_lock_simple and ipte_lock_siif.
--
--- Patch [2]: [PATCH 2/4] KVM: s390: Remove cond_resched() calls ---
commit 85d6ff7bc8ba9ff52b5d710af6d19c877a1f970f
Author: Heiko Carstens <hca@linux.ibm.com>
KVM: s390: Remove cond_resched() calls
Since [1] cond_resched() is a no-op on s390. Remove all calls.
[ ... ]
> diff --git a/arch/s390/kvm/gaccess.c b/arch/s390/kvm/gaccess.c
> index 36102b2727fbf..0d389a302a70e 100644
> --- a/arch/s390/kvm/gaccess.c
> +++ b/arch/s390/kvm/gaccess.c
> @@ -151,10 +151,8 @@ static void ipte_lock_simple(struct kvm *kvm)
> ic = &kvm->arch.sca->ipte_control;
> old = READ_ONCE(*ic);
> do {
> - if (old.k) {
> - cond_resched();
> + if (old.k)
> goto retry;
> - }
[Severity: Medium]
This isn't a bug introduced by this patch, but removing cond_resched() makes
it clear that this becomes a tight read-spin loop when old.k evaluates to true.
Since cond_resched() is a no-op, this loop continuously re-reads memory without
yielding or pausing.
Should this include a cpu_relax() to prevent saturating memory bandwidth
and starving other SMT threads on the same core?
> new = old;
> new.k = 1;
> } while (!try_cmpxchg(&ic->val, &old.val, new.val));
> @@ -189,10 +187,8 @@ static void ipte_lock_siif(struct kvm *kvm)
> ic = &kvm->arch.sca->ipte_control;
> old = READ_ONCE(*ic);
> do {
> - if (old.kg) {
> - cond_resched();
> + if (old.kg)
> goto retry;
> - }
[Severity: Medium]
This isn't a bug introduced by this patch, but similar to ipte_lock_simple(),
this creates a tight read-spin loop when old.kg evaluates to true.
Would adding cpu_relax() be appropriate here as well?
> new = old;
> new.k = 1;
> new.kh++;
--
Sashiko AI review · https://sashiko.dev/#/patchset/20260727162430.1599396-1-hca@linux.ibm.com?part=2
^ permalink raw reply [flat|nested] 9+ messages in thread
* [PATCH 3/4] s390: Remove cond_resched() calls
2026-07-27 16:24 [PATCH 0/4] s390: Remove or replace cond_resched() calls Heiko Carstens
2026-07-27 16:24 ` [PATCH 1/4] s390/crypto: Replace cond_resched() with schedule() Heiko Carstens
2026-07-27 16:24 ` [PATCH 2/4] KVM: s390: Remove cond_resched() calls Heiko Carstens
@ 2026-07-27 16:24 ` Heiko Carstens
2026-07-27 16:54 ` sashiko-bot
2026-07-27 16:24 ` [PATCH 4/4] s390/cio: " Heiko Carstens
3 siblings, 1 reply; 9+ messages in thread
From: Heiko Carstens @ 2026-07-27 16:24 UTC (permalink / raw)
To: Alexander Gordeev, Sven Schnelle, Vasily Gorbik,
Christian Borntraeger, Harald Freudenberger, Holger Dengler,
Vineeth Vijayan, Peter Oberparleiter, Janosch Frank,
Claudio Imbrenda, David Hildenbrand, Peter Zijlstra
Cc: linux-s390, linux-kernel
Since [1] cond_resched() is a no-op on s390. Remove all calls.
[1] commit 7dadeaa6e851 ("sched: Further restrict the preemption modes")
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
---
arch/s390/kernel/perf_cpum_cf.c | 1 -
arch/s390/mm/cmm.c | 2 --
arch/s390/mm/pageattr.c | 5 -----
arch/s390/mm/pgalloc.c | 1 -
arch/s390/pci/pci.c | 4 +---
5 files changed, 1 insertion(+), 12 deletions(-)
diff --git a/arch/s390/kernel/perf_cpum_cf.c b/arch/s390/kernel/perf_cpum_cf.c
index 2076ac22e2c4..5f2596be6c1e 100644
--- a/arch/s390/kernel/perf_cpum_cf.c
+++ b/arch/s390/kernel/perf_cpum_cf.c
@@ -1496,7 +1496,6 @@ static int cfset_all_copy(unsigned long arg, cpumask_t *mask)
goto out;
}
uptr += sizeof(struct s390_ctrset_cpudata) + cpuhw->used;
- cond_resched();
}
cpus = cpumask_weight(mask);
if (put_user(cpus, &ctrset_read->no_cpus))
diff --git a/arch/s390/mm/cmm.c b/arch/s390/mm/cmm.c
index eb7ef63fab1e..d342b68ee9be 100644
--- a/arch/s390/mm/cmm.c
+++ b/arch/s390/mm/cmm.c
@@ -95,7 +95,6 @@ static long cmm_alloc_pages(long nr, long *counter,
(*counter)++;
spin_unlock(&cmm_lock);
nr--;
- cond_resched();
}
return nr;
}
@@ -134,7 +133,6 @@ static long cmm_free_pages(long nr, long *counter, struct cmm_page_array **list)
inc = __cmm_free_pages(inc, counter, list);
if (inc)
break;
- cond_resched();
}
return nr + inc;
}
diff --git a/arch/s390/mm/pageattr.c b/arch/s390/mm/pageattr.c
index e6f788696dd1..1e202e3d08e7 100644
--- a/arch/s390/mm/pageattr.c
+++ b/arch/s390/mm/pageattr.c
@@ -105,7 +105,6 @@ static int walk_pte_level(pmd_t *pmdp, unsigned long addr, unsigned long end,
pgt_set((unsigned long *)ptep, pte_val(new), addr, CRDTE_DTT_PAGE);
ptep++;
addr += PAGE_SIZE;
- cond_resched();
} while (addr < end);
return 0;
}
@@ -194,7 +193,6 @@ static int walk_pmd_level(pud_t *pudp, unsigned long addr, unsigned long end,
}
pmdp++;
addr = next;
- cond_resched();
} while (addr < end);
return rc;
}
@@ -281,7 +279,6 @@ static int walk_pud_level(p4d_t *p4d, unsigned long addr, unsigned long end,
}
pudp++;
addr = next;
- cond_resched();
} while (addr < end && !rc);
return rc;
}
@@ -301,7 +298,6 @@ static int walk_p4d_level(pgd_t *pgd, unsigned long addr, unsigned long end,
rc = walk_pud_level(p4dp, addr, next, flags);
p4dp++;
addr = next;
- cond_resched();
} while (addr < end && !rc);
return rc;
}
@@ -323,7 +319,6 @@ static int change_page_attr(unsigned long addr, unsigned long end,
rc = walk_p4d_level(pgdp, addr, next, flags);
if (rc)
break;
- cond_resched();
} while (pgdp++, addr = next, addr < end && !rc);
return rc;
}
diff --git a/arch/s390/mm/pgalloc.c b/arch/s390/mm/pgalloc.c
index 7ac44543e051..9610770fcf6d 100644
--- a/arch/s390/mm/pgalloc.c
+++ b/arch/s390/mm/pgalloc.c
@@ -268,7 +268,6 @@ static int base_segment_walk(unsigned long *origin, unsigned long addr,
return rc;
if (!alloc)
base_pgt_free(table);
- cond_resched();
} while (ste++, addr = next, addr < end);
return 0;
}
diff --git a/arch/s390/pci/pci.c b/arch/s390/pci/pci.c
index 39bd2adfc240..2dec238f3f12 100644
--- a/arch/s390/pci/pci.c
+++ b/arch/s390/pci/pci.c
@@ -1173,10 +1173,8 @@ int zpci_scan_devices(void)
return rc;
zpci_add_devices(&scan_list);
- zpci_bus_for_each(zbus) {
+ zpci_bus_for_each(zbus)
zpci_bus_scan_bus(zbus);
- cond_resched();
- }
return 0;
}
--
2.53.0
^ permalink raw reply related [flat|nested] 9+ messages in thread* [PATCH 4/4] s390/cio: Remove cond_resched() calls
2026-07-27 16:24 [PATCH 0/4] s390: Remove or replace cond_resched() calls Heiko Carstens
` (2 preceding siblings ...)
2026-07-27 16:24 ` [PATCH 3/4] " Heiko Carstens
@ 2026-07-27 16:24 ` Heiko Carstens
2026-07-27 16:54 ` sashiko-bot
3 siblings, 1 reply; 9+ messages in thread
From: Heiko Carstens @ 2026-07-27 16:24 UTC (permalink / raw)
To: Alexander Gordeev, Sven Schnelle, Vasily Gorbik,
Christian Borntraeger, Harald Freudenberger, Holger Dengler,
Vineeth Vijayan, Peter Oberparleiter, Janosch Frank,
Claudio Imbrenda, David Hildenbrand, Peter Zijlstra
Cc: linux-s390, linux-kernel
Since [1] cond_resched() is a no-op on s390. Remove all calls.
[1] commit 7dadeaa6e851 ("sched: Further restrict the preemption modes")
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
---
drivers/s390/cio/css.c | 8 --------
1 file changed, 8 deletions(-)
diff --git a/drivers/s390/cio/css.c b/drivers/s390/cio/css.c
index e5a0ec6b4e3e..54b8b8639694 100644
--- a/drivers/s390/cio/css.c
+++ b/drivers/s390/cio/css.c
@@ -618,11 +618,6 @@ static int slow_eval_known_fn(struct subchannel *sch, void *data)
rc = css_evaluate_known_subchannel(sch, 1);
if (rc == -EAGAIN)
css_schedule_eval(sch->schid);
- /*
- * The loop might take long time for platforms with lots of
- * known devices. Allow scheduling here.
- */
- cond_resched();
}
return 0;
}
@@ -654,9 +649,6 @@ static int slow_eval_unknown_fn(struct subchannel_id schid, void *data)
default:
rc = 0;
}
- /* Allow scheduling here since the containing loop might
- * take a while. */
- cond_resched();
}
return rc;
}
--
2.53.0
^ permalink raw reply related [flat|nested] 9+ messages in thread