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Message-ID: <20250416163142.aKBzQeqK@linutronix.de>
Date: Wed, 16 Apr 2025 18:31:42 +0200
From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To: linux-kernel@...r.kernel.org
Cc: André Almeida <andrealmeid@...lia.com>,
Darren Hart <dvhart@...radead.org>,
Davidlohr Bueso <dave@...olabs.net>, Ingo Molnar <mingo@...hat.com>,
Juri Lelli <juri.lelli@...hat.com>,
Peter Zijlstra <peterz@...radead.org>,
Thomas Gleixner <tglx@...utronix.de>,
Valentin Schneider <vschneid@...hat.com>,
Waiman Long <longman@...hat.com>
Subject: Re: [PATCH v12 00/21] futex: Add support task local hash maps,
FUTEX2_NUMA and FUTEX2_MPOL
On 2025-04-16 18:29:00 [+0200], To linux-kernel@...r.kernel.org wrote:
> v11…v12: https://lore.kernel.org/all/20250407155742.968816-1-bigeasy@linutronix.de
A diff excluding the tools/testing/ changes:
diff --git a/include/linux/futex.h b/include/linux/futex.h
index 96c7229856d97..eccc99751bd94 100644
--- a/include/linux/futex.h
+++ b/include/linux/futex.h
@@ -109,7 +109,7 @@ static inline long do_futex(u32 __user *uaddr, int op, u32 val,
{
return -EINVAL;
}
-static inline int futex_hash_prctl(unsigned long arg2, unsigned long arg3)
+static inline int futex_hash_prctl(unsigned long arg2, unsigned long arg3, unsigned long arg4)
{
return -EINVAL;
}
diff --git a/kernel/futex/core.c b/kernel/futex/core.c
index 44bb9eeb0a9c1..ee1d7182ce0c0 100644
--- a/kernel/futex/core.c
+++ b/kernel/futex/core.c
@@ -551,6 +551,7 @@ int get_futex_key(u32 __user *uaddr, unsigned int flags, union futex_key *key,
struct folio *folio;
struct address_space *mapping;
int node, err, size, ro = 0;
+ bool node_updated = false;
bool fshared;
fshared = flags & FLAGS_SHARED;
@@ -575,24 +576,29 @@ int get_futex_key(u32 __user *uaddr, unsigned int flags, union futex_key *key,
node = FUTEX_NO_NODE;
if (flags & FLAGS_NUMA) {
- u32 __user *naddr = uaddr + size / 2;
+ u32 __user *naddr = (void *)uaddr + size / 2;
if (futex_get_value(&node, naddr))
return -EFAULT;
- if (node >= MAX_NUMNODES || !node_possible(node))
+ if (node != FUTEX_NO_NODE &&
+ (node >= MAX_NUMNODES || !node_possible(node)))
return -EINVAL;
}
- if (node == FUTEX_NO_NODE && (flags & FLAGS_MPOL))
+ if (node == FUTEX_NO_NODE && (flags & FLAGS_MPOL)) {
node = futex_mpol(mm, address);
+ node_updated = true;
+ }
if (flags & FLAGS_NUMA) {
- u32 __user *naddr = uaddr + size / 2;
+ u32 __user *naddr = (void *)uaddr + size / 2;
- if (node == FUTEX_NO_NODE)
+ if (node == FUTEX_NO_NODE) {
node = numa_node_id();
- if (futex_put_value(node, naddr))
+ node_updated = true;
+ }
+ if (node_updated && futex_put_value(node, naddr))
return -EFAULT;
}
@@ -1573,6 +1579,8 @@ static int futex_hash_allocate(unsigned int hash_slots, unsigned int immutable,
if (hash_slots && (hash_slots == 1 || !is_power_of_2(hash_slots)))
return -EINVAL;
+ if (immutable > 2)
+ return -EINVAL;
/*
* Once we've disabled the global hash there is no way back.
@@ -1586,7 +1594,7 @@ static int futex_hash_allocate(unsigned int hash_slots, unsigned int immutable,
}
}
- fph = kvzalloc(struct_size(fph, queues, hash_slots), GFP_KERNEL_ACCOUNT);
+ fph = kvzalloc(struct_size(fph, queues, hash_slots), GFP_KERNEL_ACCOUNT | __GFP_NOWARN);
if (!fph)
return -ENOMEM;
diff --git a/kernel/futex/futex.h b/kernel/futex/futex.h
index 004e4dbee4f93..069fc2a83080d 100644
--- a/kernel/futex/futex.h
+++ b/kernel/futex/futex.h
@@ -55,7 +55,7 @@ static inline unsigned int futex_to_flags(unsigned int op)
return flags;
}
-#define FUTEX2_VALID_MASK (FUTEX2_SIZE_MASK | FUTEX2_NUMA | FUTEX2_PRIVATE)
+#define FUTEX2_VALID_MASK (FUTEX2_SIZE_MASK | FUTEX2_NUMA | FUTEX2_MPOL | FUTEX2_PRIVATE)
/* FUTEX2_ to FLAGS_ */
static inline unsigned int futex2_to_flags(unsigned int flags2)
diff --git a/kernel/futex/pi.c b/kernel/futex/pi.c
index 356e52c17d3c5..dacb2330f1fbc 100644
--- a/kernel/futex/pi.c
+++ b/kernel/futex/pi.c
@@ -993,6 +993,16 @@ int futex_lock_pi(u32 __user *uaddr, unsigned int flags, ktime_t *time, int tryl
goto no_block;
}
+ /*
+ * Caution; releasing @hb in-scope. The hb->lock is still locked
+ * while the reference is dropped. The reference can not be dropped
+ * after the unlock because if a user initiated resize is in progress
+ * then we might need to wake him. This can not be done after the
+ * rt_mutex_pre_schedule() invocation. The hb will remain valid because
+ * the thread, performing resize, will block on hb->lock during
+ * the requeue.
+ */
+ futex_hash_put(no_free_ptr(hb));
/*
* Must be done before we enqueue the waiter, here is unfortunately
* under the hb lock, but that *should* work because it does nothing.
@@ -1016,10 +1026,6 @@ int futex_lock_pi(u32 __user *uaddr, unsigned int flags, ktime_t *time, int tryl
*/
raw_spin_lock_irq(&q.pi_state->pi_mutex.wait_lock);
spin_unlock(q.lock_ptr);
- /*
- * Caution; releasing @hb in-scope.
- */
- futex_hash_put(no_free_ptr(hb));
/*
* __rt_mutex_start_proxy_lock() unconditionally enqueues the @rt_waiter
* such that futex_unlock_pi() is guaranteed to observe the waiter when
diff --git a/tools/perf/bench/futex.c b/tools/perf/bench/futex.c
index bed3b6e46d109..02ae6c52ba881 100644
--- a/tools/perf/bench/futex.c
+++ b/tools/perf/bench/futex.c
@@ -31,20 +31,25 @@ void futex_print_nbuckets(struct bench_futex_parameters *params)
if (params->nbuckets >= 0) {
if (ret != params->nbuckets) {
if (ret < 0) {
- printf("Can't query number of buckets: %d/%m\n", ret);
+ printf("Can't query number of buckets: %m\n");
err(EXIT_FAILURE, "prctl(PR_FUTEX_HASH)");
}
printf("Requested number of hash buckets does not currently used.\n");
printf("Requested: %d in usage: %d\n", params->nbuckets, ret);
err(EXIT_FAILURE, "prctl(PR_FUTEX_HASH)");
}
- ret = prctl(PR_FUTEX_HASH, PR_FUTEX_HASH_GET_IMMUTABLE);
- if (params->nbuckets == 0)
+ if (params->nbuckets == 0) {
ret = asprintf(&futex_hash_mode, "Futex hashing: global hash");
- else
+ } else {
+ ret = prctl(PR_FUTEX_HASH, PR_FUTEX_HASH_GET_IMMUTABLE);
+ if (ret < 0) {
+ printf("Can't check if the hash is immutable: %m\n");
+ err(EXIT_FAILURE, "prctl(PR_FUTEX_HASH)");
+ }
ret = asprintf(&futex_hash_mode, "Futex hashing: %d hash buckets %s",
params->nbuckets,
ret == 1 ? "(immutable)" : "");
+ }
} else {
if (ret <= 0) {
ret = asprintf(&futex_hash_mode, "Futex hashing: global hash");
Sebastian
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