From 93a4b36ef3cf4ce5e6a7e7a7686181de76e246a1 Mon Sep 17 00:00:00 2001 From: Nirbhay Sharma Date: Fri, 3 Oct 2025 17:15:55 +0530 Subject: [PATCH 1/4] cgroup: Fix seqcount lockdep assertion in cgroup freezer MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit The commit afa3701c0e45 ("cgroup: cgroup.stat.local time accounting") introduced a seqcount to track freeze timing but initialized it as a plain seqcount_t using seqcount_init(). However, the write-side critical section in cgroup_do_freeze() holds the css_set_lock spinlock while calling write_seqcount_begin(). On PREEMPT_RT kernels, spinlocks do not disable preemption, causing the lockdep assertion for a plain seqcount_t, which checks for preemption being disabled, to fail. This triggers the following warning: WARNING: CPU: 0 PID: 9692 at include/linux/seqlock.h:221 Fix this by changing the type to seqcount_spinlock_t and initializing it with seqcount_spinlock_init() to associate css_set_lock with the seqcount. This allows lockdep to correctly validate that the spinlock is held during write operations, resolving the assertion failure on all kernel configurations. Reported-by: syzbot+27a2519eb4dad86d0156@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=27a2519eb4dad86d0156 Fixes: afa3701c0e45 ("cgroup: cgroup.stat.local time accounting") Signed-off-by: Nirbhay Sharma Link: https://lore.kernel.org/r/20251002165510.KtY3IT--@linutronix.de/ Acked-by: Michal Koutný Signed-off-by: Tejun Heo --- include/linux/cgroup-defs.h | 2 +- kernel/cgroup/cgroup.c | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-) diff --git a/include/linux/cgroup-defs.h b/include/linux/cgroup-defs.h index 93318fce31f3..b760a3c470a5 100644 --- a/include/linux/cgroup-defs.h +++ b/include/linux/cgroup-defs.h @@ -452,7 +452,7 @@ struct cgroup_freezer_state { int nr_frozen_tasks; /* Freeze time data consistency protection */ - seqcount_t freeze_seq; + seqcount_spinlock_t freeze_seq; /* * Most recent time the cgroup was requested to freeze. diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c index 6ae5f48cf64e..fdee387f0d6b 100644 --- a/kernel/cgroup/cgroup.c +++ b/kernel/cgroup/cgroup.c @@ -5892,7 +5892,7 @@ static struct cgroup *cgroup_create(struct cgroup *parent, const char *name, * if the parent has to be frozen, the child has too. */ cgrp->freezer.e_freeze = parent->freezer.e_freeze; - seqcount_init(&cgrp->freezer.freeze_seq); + seqcount_spinlock_init(&cgrp->freezer.freeze_seq, &css_set_lock); if (cgrp->freezer.e_freeze) { /* * Set the CGRP_FREEZE flag, so when a process will be From 3f9c60f4d3cc3e7f4dd7cac05011ea06d512050f Mon Sep 17 00:00:00 2001 From: Sebastian Chlad Date: Wed, 15 Oct 2025 12:33:56 +0200 Subject: [PATCH 2/4] selftests: cgroup: add values_close_report helper Some cgroup selftests, such as test_cpu, occasionally fail by a very small margin and if run in the CI context, it is useful to have detailed diagnostic output to understand the deviation. Introduce a values_close_report() helper which performs the same comparison as values_close(), but prints detailed information when the values differ beyond the allowed tolerance. Signed-off-by: Sebastian Chlad Signed-off-by: Tejun Heo --- .../cgroup/lib/include/cgroup_util.h | 20 +++++++++++++++++++ 1 file changed, 20 insertions(+) diff --git a/tools/testing/selftests/cgroup/lib/include/cgroup_util.h b/tools/testing/selftests/cgroup/lib/include/cgroup_util.h index 9dc90a1b386d..7ab2824ed7b5 100644 --- a/tools/testing/selftests/cgroup/lib/include/cgroup_util.h +++ b/tools/testing/selftests/cgroup/lib/include/cgroup_util.h @@ -25,6 +25,26 @@ static inline int values_close(long a, long b, int err) return labs(a - b) <= (a + b) / 100 * err; } +/* + * Checks if two given values differ by less than err% of their sum and assert + * with detailed debug info if not. + */ +static inline int values_close_report(long a, long b, int err) +{ + long diff = labs(a - b); + long limit = (a + b) / 100 * err; + double actual_err = (a + b) ? (100.0 * diff / (a + b)) : 0.0; + int close = diff <= limit; + + if (!close) + fprintf(stderr, + "[FAIL] actual=%ld expected=%ld | diff=%ld | limit=%ld | " + "tolerance=%d%% | actual_error=%.2f%%\n", + a, b, diff, limit, err, actual_err); + + return close; +} + extern ssize_t read_text(const char *path, char *buf, size_t max_len); extern ssize_t write_text(const char *path, char *buf, ssize_t len); From 4cdde87d723a0552f475c8c6b0db472a6945125f Mon Sep 17 00:00:00 2001 From: Sebastian Chlad Date: Wed, 15 Oct 2025 12:33:57 +0200 Subject: [PATCH 3/4] selftests: cgroup: Use values_close_report in test_cpu Convert test_cpu to use the newly added values_close_report() helper to print detailed diagnostics when a tolerance check fails. This provides clearer insight into deviations while run in the CI. Signed-off-by: Sebastian Chlad Signed-off-by: Tejun Heo --- tools/testing/selftests/cgroup/test_cpu.c | 18 +++++++++--------- 1 file changed, 9 insertions(+), 9 deletions(-) diff --git a/tools/testing/selftests/cgroup/test_cpu.c b/tools/testing/selftests/cgroup/test_cpu.c index 2a60e6c41940..d54e2317efff 100644 --- a/tools/testing/selftests/cgroup/test_cpu.c +++ b/tools/testing/selftests/cgroup/test_cpu.c @@ -219,7 +219,7 @@ static int test_cpucg_stats(const char *root) if (user_usec <= 0) goto cleanup; - if (!values_close(usage_usec, expected_usage_usec, 1)) + if (!values_close_report(usage_usec, expected_usage_usec, 1)) goto cleanup; ret = KSFT_PASS; @@ -291,7 +291,7 @@ static int test_cpucg_nice(const char *root) user_usec = cg_read_key_long(cpucg, "cpu.stat", "user_usec"); nice_usec = cg_read_key_long(cpucg, "cpu.stat", "nice_usec"); - if (!values_close(nice_usec, expected_nice_usec, 1)) + if (!values_close_report(nice_usec, expected_nice_usec, 1)) goto cleanup; ret = KSFT_PASS; @@ -404,7 +404,7 @@ overprovision_validate(const struct cpu_hogger *children, int num_children) goto cleanup; delta = children[i + 1].usage - children[i].usage; - if (!values_close(delta, children[0].usage, 35)) + if (!values_close_report(delta, children[0].usage, 35)) goto cleanup; } @@ -444,7 +444,7 @@ underprovision_validate(const struct cpu_hogger *children, int num_children) int ret = KSFT_FAIL, i; for (i = 0; i < num_children - 1; i++) { - if (!values_close(children[i + 1].usage, children[0].usage, 15)) + if (!values_close_report(children[i + 1].usage, children[0].usage, 15)) goto cleanup; } @@ -573,16 +573,16 @@ run_cpucg_nested_weight_test(const char *root, bool overprovisioned) nested_leaf_usage = leaf[1].usage + leaf[2].usage; if (overprovisioned) { - if (!values_close(leaf[0].usage, nested_leaf_usage, 15)) + if (!values_close_report(leaf[0].usage, nested_leaf_usage, 15)) goto cleanup; - } else if (!values_close(leaf[0].usage * 2, nested_leaf_usage, 15)) + } else if (!values_close_report(leaf[0].usage * 2, nested_leaf_usage, 15)) goto cleanup; child_usage = cg_read_key_long(child, "cpu.stat", "usage_usec"); if (child_usage <= 0) goto cleanup; - if (!values_close(child_usage, nested_leaf_usage, 1)) + if (!values_close_report(child_usage, nested_leaf_usage, 1)) goto cleanup; ret = KSFT_PASS; @@ -691,7 +691,7 @@ static int test_cpucg_max(const char *root) expected_usage_usec = n_periods * quota_usec + MIN(remainder_usec, quota_usec); - if (!values_close(usage_usec, expected_usage_usec, 10)) + if (!values_close_report(usage_usec, expected_usage_usec, 10)) goto cleanup; ret = KSFT_PASS; @@ -762,7 +762,7 @@ static int test_cpucg_max_nested(const char *root) expected_usage_usec = n_periods * quota_usec + MIN(remainder_usec, quota_usec); - if (!values_close(usage_usec, expected_usage_usec, 10)) + if (!values_close_report(usage_usec, expected_usage_usec, 10)) goto cleanup; ret = KSFT_PASS; From 0fbbcab7f9082cdc233da5e5e353f69830f11956 Mon Sep 17 00:00:00 2001 From: Randy Dunlap Date: Fri, 17 Oct 2025 00:07:42 -0700 Subject: [PATCH 4/4] cgroup/misc: fix misc_res_type kernel-doc warning Format the kernel-doc for SCALE_HW_CALIB_INVALID correctly to avoid a kernel-doc warning: Warning: include/linux/misc_cgroup.h:26 Enum value 'MISC_CG_RES_TDX' not described in enum 'misc_res_type' Fixes: 7c035bea9407 ("KVM: TDX: Register TDX host key IDs to cgroup misc controller") Signed-off-by: Randy Dunlap Signed-off-by: Tejun Heo --- include/linux/misc_cgroup.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/include/linux/misc_cgroup.h b/include/linux/misc_cgroup.h index 71cf5bfc6349..0cb36a3ffc47 100644 --- a/include/linux/misc_cgroup.h +++ b/include/linux/misc_cgroup.h @@ -19,7 +19,7 @@ enum misc_res_type { MISC_CG_RES_SEV_ES, #endif #ifdef CONFIG_INTEL_TDX_HOST - /* Intel TDX HKIDs resource */ + /** @MISC_CG_RES_TDX: Intel TDX HKIDs resource */ MISC_CG_RES_TDX, #endif /** @MISC_CG_RES_TYPES: count of enum misc_res_type constants */