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Message-Id: <20251215044919.460086-10-ankur.a.arora@oracle.com>
Date: Sun, 14 Dec 2025 20:49:16 -0800
From: Ankur Arora <ankur.a.arora@...cle.com>
To: linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
linux-arm-kernel@...ts.infradead.org, linux-pm@...r.kernel.org,
bpf@...r.kernel.org
Cc: arnd@...db.de, catalin.marinas@....com, will@...nel.org,
peterz@...radead.org, akpm@...ux-foundation.org, mark.rutland@....com,
harisokn@...zon.com, cl@...two.org, ast@...nel.org, rafael@...nel.org,
daniel.lezcano@...aro.org, memxor@...il.com, zhenglifeng1@...wei.com,
xueshuai@...ux.alibaba.com, joao.m.martins@...cle.com,
boris.ostrovsky@...cle.com, konrad.wilk@...cle.com,
Ankur Arora <ankur.a.arora@...cle.com>
Subject: [PATCH v8 09/12] bpf/rqspinlock: switch check_timeout() to a clock interface
check_timeout() gets the current time value and depending on how
much time has passed, checks for deadlock or times out, returning 0
or -errno on deadlock or timeout.
Switch this out to a clock style interface, where it functions as a
clock in the "lock-domain", returning the current time until a
deadlock or timeout occurs. Once a deadlock or timeout has occurred,
it stops functioning as a clock and returns error.
Cc: Kumar Kartikeya Dwivedi <memxor@...il.com>
Cc: Alexei Starovoitov <ast@...nel.org>
Cc: bpf@...r.kernel.org
Signed-off-by: Ankur Arora <ankur.a.arora@...cle.com>
---
kernel/bpf/rqspinlock.c | 41 +++++++++++++++++++++++++++--------------
1 file changed, 27 insertions(+), 14 deletions(-)
diff --git a/kernel/bpf/rqspinlock.c b/kernel/bpf/rqspinlock.c
index f7d0c8d4644e..ac9b3572e42f 100644
--- a/kernel/bpf/rqspinlock.c
+++ b/kernel/bpf/rqspinlock.c
@@ -196,8 +196,12 @@ static noinline int check_deadlock_ABBA(rqspinlock_t *lock, u32 mask)
return 0;
}
-static noinline int check_timeout(rqspinlock_t *lock, u32 mask,
- struct rqspinlock_timeout *ts)
+/*
+ * Returns current monotonic time in ns on success or, negative errno
+ * value on failure due to timeout expiration or detection of deadlock.
+ */
+static noinline s64 clock_deadlock(rqspinlock_t *lock, u32 mask,
+ struct rqspinlock_timeout *ts)
{
u64 prev = ts->cur;
u64 time;
@@ -207,7 +211,7 @@ static noinline int check_timeout(rqspinlock_t *lock, u32 mask,
return -EDEADLK;
ts->cur = ktime_get_mono_fast_ns();
ts->timeout_end = ts->cur + ts->duration;
- return 0;
+ return (s64)ts->cur;
}
time = ktime_get_mono_fast_ns();
@@ -219,11 +223,15 @@ static noinline int check_timeout(rqspinlock_t *lock, u32 mask,
* checks.
*/
if (prev + NSEC_PER_MSEC < time) {
+ int ret;
ts->cur = time;
- return check_deadlock_ABBA(lock, mask);
+ ret = check_deadlock_ABBA(lock, mask);
+ if (ret)
+ return ret;
+
}
- return 0;
+ return (s64)time;
}
/*
@@ -234,12 +242,12 @@ static noinline int check_timeout(rqspinlock_t *lock, u32 mask,
#define RES_CHECK_TIMEOUT(ts, ret, mask) \
({ \
if (!(ts).spin++) \
- (ret) = check_timeout((lock), (mask), &(ts)); \
+ (ret) = clock_deadlock((lock), (mask), &(ts));\
(ret); \
})
#else
#define RES_CHECK_TIMEOUT(ts, ret, mask) \
- ({ (ret) = check_timeout((lock), (mask), &(ts)); })
+ ({ (ret) = clock_deadlock((lock), (mask), &(ts)); })
#endif
/*
@@ -261,7 +269,8 @@ static noinline int check_timeout(rqspinlock_t *lock, u32 mask,
int __lockfunc resilient_tas_spin_lock(rqspinlock_t *lock)
{
struct rqspinlock_timeout ts;
- int val, ret = 0;
+ s64 ret = 0;
+ int val;
RES_INIT_TIMEOUT(ts);
/*
@@ -280,7 +289,7 @@ int __lockfunc resilient_tas_spin_lock(rqspinlock_t *lock)
val = atomic_read(&lock->val);
if (val || !atomic_try_cmpxchg(&lock->val, &val, 1)) {
- if (RES_CHECK_TIMEOUT(ts, ret, ~0u))
+ if (RES_CHECK_TIMEOUT(ts, ret, ~0u) < 0)
goto out;
cpu_relax();
goto retry;
@@ -339,6 +348,7 @@ int __lockfunc resilient_queued_spin_lock_slowpath(rqspinlock_t *lock, u32 val)
{
struct mcs_spinlock *prev, *next, *node;
struct rqspinlock_timeout ts;
+ s64 timeout_err = 0;
int idx, ret = 0;
u32 old, tail;
@@ -405,10 +415,10 @@ int __lockfunc resilient_queued_spin_lock_slowpath(rqspinlock_t *lock, u32 val)
*/
if (val & _Q_LOCKED_MASK) {
RES_RESET_TIMEOUT(ts, RES_DEF_TIMEOUT);
- res_smp_cond_load_acquire(&lock->locked, !VAL || RES_CHECK_TIMEOUT(ts, ret, _Q_LOCKED_MASK));
+ res_smp_cond_load_acquire(&lock->locked, !VAL || RES_CHECK_TIMEOUT(ts, timeout_err, _Q_LOCKED_MASK) < 0);
}
- if (ret) {
+ if (timeout_err < 0) {
/*
* We waited for the locked bit to go back to 0, as the pending
* waiter, but timed out. We need to clear the pending bit since
@@ -420,6 +430,7 @@ int __lockfunc resilient_queued_spin_lock_slowpath(rqspinlock_t *lock, u32 val)
*/
clear_pending(lock);
lockevent_inc(rqspinlock_lock_timeout);
+ ret = timeout_err;
goto err_release_entry;
}
@@ -567,18 +578,19 @@ int __lockfunc resilient_queued_spin_lock_slowpath(rqspinlock_t *lock, u32 val)
*/
RES_RESET_TIMEOUT(ts, RES_DEF_TIMEOUT * 2);
val = res_atomic_cond_read_acquire(&lock->val, !(VAL & _Q_LOCKED_PENDING_MASK) ||
- RES_CHECK_TIMEOUT(ts, ret, _Q_LOCKED_PENDING_MASK));
+ RES_CHECK_TIMEOUT(ts, timeout_err, _Q_LOCKED_PENDING_MASK) < 0);
/* Disable queue destruction when we detect deadlocks. */
- if (ret == -EDEADLK) {
+ if (timeout_err == -EDEADLK) {
if (!next)
next = smp_cond_load_relaxed(&node->next, (VAL));
arch_mcs_spin_unlock_contended(&next->locked);
+ ret = timeout_err;
goto err_release_node;
}
waitq_timeout:
- if (ret) {
+ if (timeout_err < 0) {
/*
* If the tail is still pointing to us, then we are the final waiter,
* and are responsible for resetting the tail back to 0. Otherwise, if
@@ -608,6 +620,7 @@ int __lockfunc resilient_queued_spin_lock_slowpath(rqspinlock_t *lock, u32 val)
WRITE_ONCE(next->locked, RES_TIMEOUT_VAL);
}
lockevent_inc(rqspinlock_lock_timeout);
+ ret = timeout_err;
goto err_release_node;
}
--
2.31.1
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