From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: linux-kernel@vger.kernel.org, stable@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
"Peter Zijlstra (Intel)" <peterz@infradead.org>,
juri.lelli@arm.com, bigeasy@linutronix.de, xlpang@redhat.com,
rostedt@goodmis.org, mathieu.desnoyers@efficios.com,
jdesfossez@efficios.com, dvhart@infradead.org,
bristot@redhat.com, Thomas Gleixner <tglx@linutronix.de>,
Ben Hutchings <ben@decadent.org.uk>
Subject: [PATCH 4.9 03/41] futex: Pull rt_mutex_futex_unlock() out from under hb->lock
Date: Fri, 5 Mar 2021 13:22:10 +0100 [thread overview]
Message-ID: <20210305120851.434265124@linuxfoundation.org> (raw)
In-Reply-To: <20210305120851.255002428@linuxfoundation.org>
From: Ben Hutchings <ben@decadent.org.uk>
From: Peter Zijlstra <peterz@infradead.org>
commit 16ffa12d742534d4ff73e8b3a4e81c1de39196f0 upstream.
There's a number of 'interesting' problems, all caused by holding
hb->lock while doing the rt_mutex_unlock() equivalient.
Notably:
- a PI inversion on hb->lock; and,
- a SCHED_DEADLINE crash because of pointer instability.
The previous changes:
- changed the locking rules to cover {uval,pi_state} with wait_lock.
- allow to do rt_mutex_futex_unlock() without dropping wait_lock; which in
turn allows to rely on wait_lock atomicity completely.
- simplified the waiter conundrum.
It's now sufficient to hold rtmutex::wait_lock and a reference on the
pi_state to protect the state consistency, so hb->lock can be dropped
before calling rt_mutex_futex_unlock().
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: juri.lelli@arm.com
Cc: bigeasy@linutronix.de
Cc: xlpang@redhat.com
Cc: rostedt@goodmis.org
Cc: mathieu.desnoyers@efficios.com
Cc: jdesfossez@efficios.com
Cc: dvhart@infradead.org
Cc: bristot@redhat.com
Link: http://lkml.kernel.org/r/20170322104151.900002056@infradead.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
[bwh: Backported to 4.9: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
kernel/futex.c | 111 ++++++++++++++++++++++++++++++++++-----------------------
1 file changed, 68 insertions(+), 43 deletions(-)
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -966,10 +966,12 @@ static void exit_pi_state_list(struct ta
pi_state->owner = NULL;
raw_spin_unlock_irq(&curr->pi_lock);
- rt_mutex_futex_unlock(&pi_state->pi_mutex);
-
+ get_pi_state(pi_state);
spin_unlock(&hb->lock);
+ rt_mutex_futex_unlock(&pi_state->pi_mutex);
+ put_pi_state(pi_state);
+
raw_spin_lock_irq(&curr->pi_lock);
}
raw_spin_unlock_irq(&curr->pi_lock);
@@ -1083,6 +1085,11 @@ static int attach_to_pi_state(u32 __user
* has dropped the hb->lock in between queue_me() and unqueue_me_pi(),
* which in turn means that futex_lock_pi() still has a reference on
* our pi_state.
+ *
+ * The waiter holding a reference on @pi_state also protects against
+ * the unlocked put_pi_state() in futex_unlock_pi(), futex_lock_pi()
+ * and futex_wait_requeue_pi() as it cannot go to 0 and consequently
+ * free pi_state before we can take a reference ourselves.
*/
WARN_ON(!atomic_read(&pi_state->refcount));
@@ -1537,48 +1544,40 @@ static void mark_wake_futex(struct wake_
q->lock_ptr = NULL;
}
-static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_q *top_waiter,
- struct futex_hash_bucket *hb)
+/*
+ * Caller must hold a reference on @pi_state.
+ */
+static int wake_futex_pi(u32 __user *uaddr, u32 uval, struct futex_pi_state *pi_state)
{
- struct task_struct *new_owner;
- struct futex_pi_state *pi_state = top_waiter->pi_state;
u32 uninitialized_var(curval), newval;
+ struct task_struct *new_owner;
+ bool deboost = false;
WAKE_Q(wake_q);
- bool deboost;
int ret = 0;
- if (!pi_state)
- return -EINVAL;
-
- /*
- * If current does not own the pi_state then the futex is
- * inconsistent and user space fiddled with the futex value.
- */
- if (pi_state->owner != current)
- return -EINVAL;
-
raw_spin_lock_irq(&pi_state->pi_mutex.wait_lock);
new_owner = rt_mutex_next_owner(&pi_state->pi_mutex);
-
- /*
- * When we interleave with futex_lock_pi() where it does
- * rt_mutex_timed_futex_lock(), we might observe @top_waiter futex_q waiter,
- * but the rt_mutex's wait_list can be empty (either still, or again,
- * depending on which side we land).
- *
- * When this happens, give up our locks and try again, giving the
- * futex_lock_pi() instance time to complete, either by waiting on the
- * rtmutex or removing itself from the futex queue.
- */
if (!new_owner) {
- raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
- return -EAGAIN;
+ /*
+ * Since we held neither hb->lock nor wait_lock when coming
+ * into this function, we could have raced with futex_lock_pi()
+ * such that we might observe @this futex_q waiter, but the
+ * rt_mutex's wait_list can be empty (either still, or again,
+ * depending on which side we land).
+ *
+ * When this happens, give up our locks and try again, giving
+ * the futex_lock_pi() instance time to complete, either by
+ * waiting on the rtmutex or removing itself from the futex
+ * queue.
+ */
+ ret = -EAGAIN;
+ goto out_unlock;
}
/*
- * We pass it to the next owner. The WAITERS bit is always
- * kept enabled while there is PI state around. We cleanup the
- * owner died bit, because we are the owner.
+ * We pass it to the next owner. The WAITERS bit is always kept
+ * enabled while there is PI state around. We cleanup the owner
+ * died bit, because we are the owner.
*/
newval = FUTEX_WAITERS | task_pid_vnr(new_owner);
@@ -1611,15 +1610,15 @@ static int wake_futex_pi(u32 __user *uad
deboost = __rt_mutex_futex_unlock(&pi_state->pi_mutex, &wake_q);
}
+out_unlock:
raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
- spin_unlock(&hb->lock);
if (deboost) {
wake_up_q(&wake_q);
rt_mutex_adjust_prio(current);
}
- return 0;
+ return ret;
}
/*
@@ -2493,7 +2492,7 @@ retry:
if (get_futex_value_locked(&uval, uaddr))
goto handle_fault;
- while (1) {
+ for (;;) {
newval = (uval & FUTEX_OWNER_DIED) | newtid;
if (cmpxchg_futex_value_locked(&curval, uaddr, uval, newval))
@@ -3006,10 +3005,36 @@ retry:
*/
top_waiter = futex_top_waiter(hb, &key);
if (top_waiter) {
- ret = wake_futex_pi(uaddr, uval, top_waiter, hb);
+ struct futex_pi_state *pi_state = top_waiter->pi_state;
+
+ ret = -EINVAL;
+ if (!pi_state)
+ goto out_unlock;
+
/*
- * In case of success wake_futex_pi dropped the hash
- * bucket lock.
+ * If current does not own the pi_state then the futex is
+ * inconsistent and user space fiddled with the futex value.
+ */
+ if (pi_state->owner != current)
+ goto out_unlock;
+
+ /*
+ * Grab a reference on the pi_state and drop hb->lock.
+ *
+ * The reference ensures pi_state lives, dropping the hb->lock
+ * is tricky.. wake_futex_pi() will take rt_mutex::wait_lock to
+ * close the races against futex_lock_pi(), but in case of
+ * _any_ fail we'll abort and retry the whole deal.
+ */
+ get_pi_state(pi_state);
+ spin_unlock(&hb->lock);
+
+ ret = wake_futex_pi(uaddr, uval, pi_state);
+
+ put_pi_state(pi_state);
+
+ /*
+ * Success, we're done! No tricky corner cases.
*/
if (!ret)
goto out_putkey;
@@ -3024,7 +3049,6 @@ retry:
* setting the FUTEX_WAITERS bit. Try again.
*/
if (ret == -EAGAIN) {
- spin_unlock(&hb->lock);
put_futex_key(&key);
goto retry;
}
@@ -3032,7 +3056,7 @@ retry:
* wake_futex_pi has detected invalid state. Tell user
* space.
*/
- goto out_unlock;
+ goto out_putkey;
}
/*
@@ -3042,8 +3066,10 @@ retry:
* preserve the WAITERS bit not the OWNER_DIED one. We are the
* owner.
*/
- if (cmpxchg_futex_value_locked(&curval, uaddr, uval, 0))
+ if (cmpxchg_futex_value_locked(&curval, uaddr, uval, 0)) {
+ spin_unlock(&hb->lock);
goto pi_faulted;
+ }
/*
* If uval has changed, let user space handle it.
@@ -3057,7 +3083,6 @@ out_putkey:
return ret;
pi_faulted:
- spin_unlock(&hb->lock);
put_futex_key(&key);
ret = fault_in_user_writeable(uaddr);
next prev parent reply other threads:[~2021-03-05 12:41 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-05 12:22 [PATCH 4.9 00/41] 4.9.260-rc1 review Greg Kroah-Hartman
2021-03-05 12:22 ` [PATCH 4.9 01/41] futex: Cleanup variable names for futex_top_waiter() Greg Kroah-Hartman
2021-03-05 12:22 ` [PATCH 4.9 02/41] futex: Cleanup refcounting Greg Kroah-Hartman
2021-03-05 12:22 ` Greg Kroah-Hartman [this message]
2021-03-05 12:22 ` [PATCH 4.9 04/41] futex: Futex_unlock_pi() determinism Greg Kroah-Hartman
2021-03-05 12:22 ` [PATCH 4.9 05/41] futex: Fix pi_state->owner serialization Greg Kroah-Hartman
2021-03-05 12:22 ` [PATCH 4.9 06/41] futex: Fix more put_pi_state() vs. exit_pi_state_list() races Greg Kroah-Hartman
2021-03-05 12:22 ` [PATCH 4.9 07/41] futex: Dont enable IRQs unconditionally in put_pi_state() Greg Kroah-Hartman
2021-03-05 12:22 ` [PATCH 4.9 08/41] net: usb: qmi_wwan: support ZTE P685M modem Greg Kroah-Hartman
2021-03-05 12:22 ` [PATCH 4.9 09/41] arm: kprobes: Allow to handle reentered kprobe on single-stepping Greg Kroah-Hartman
2021-03-05 12:22 ` [PATCH 4.9 10/41] scripts: use pkg-config to locate libcrypto Greg Kroah-Hartman
2021-03-05 12:22 ` [PATCH 4.9 11/41] scripts: set proper OpenSSL include dir also for sign-file Greg Kroah-Hartman
2021-03-05 12:22 ` [PATCH 4.9 12/41] hugetlb: fix update_and_free_page contig page struct assumption Greg Kroah-Hartman
2021-03-05 12:22 ` [PATCH 4.9 13/41] printk: fix deadlock when kernel panic Greg Kroah-Hartman
2021-03-05 12:22 ` [PATCH 4.9 14/41] arm64: Remove redundant mov from LL/SC cmpxchg Greg Kroah-Hartman
2021-03-05 12:22 ` [PATCH 4.9 15/41] arm64: Avoid redundant type conversions in xchg() and cmpxchg() Greg Kroah-Hartman
2021-03-05 12:22 ` [PATCH 4.9 16/41] arm64: cmpxchg: Use "K" instead of "L" for ll/sc immediate constraint Greg Kroah-Hartman
2021-03-05 12:22 ` [PATCH 4.9 17/41] arm64: Use correct ll/sc atomic constraints Greg Kroah-Hartman
2021-03-05 12:22 ` [PATCH 4.9 18/41] JFS: more checks for invalid superblock Greg Kroah-Hartman
2021-03-05 12:22 ` [PATCH 4.9 19/41] xfs: Fix assert failure in xfs_setattr_size() Greg Kroah-Hartman
2021-03-05 12:22 ` [PATCH 4.9 20/41] smackfs: restrict bytes count in smackfs write functions Greg Kroah-Hartman
2021-03-05 12:22 ` [PATCH 4.9 21/41] net: fix up truesize of cloned skb in skb_prepare_for_shift() Greg Kroah-Hartman
2021-03-05 12:22 ` [PATCH 4.9 22/41] mm/hugetlb.c: fix unnecessary address expansion of pmd sharing Greg Kroah-Hartman
2021-03-05 12:22 ` [PATCH 4.9 23/41] staging: fwserial: Fix error handling in fwserial_create Greg Kroah-Hartman
2021-03-05 12:22 ` [PATCH 4.9 24/41] x86/reboot: Add Zotac ZBOX CI327 nano PCI reboot quirk Greg Kroah-Hartman
2021-03-05 12:22 ` [PATCH 4.9 25/41] vt/consolemap: do font sum unsigned Greg Kroah-Hartman
2021-03-05 12:22 ` [PATCH 4.9 26/41] wlcore: Fix command execute failure 19 for wl12xx Greg Kroah-Hartman
2021-03-05 12:22 ` [PATCH 4.9 27/41] pktgen: fix misuse of BUG_ON() in pktgen_thread_worker() Greg Kroah-Hartman
2021-03-05 12:22 ` [PATCH 4.9 28/41] ath10k: fix wmi mgmt tx queue full due to race condition Greg Kroah-Hartman
2021-03-05 12:22 ` [PATCH 4.9 29/41] x86/build: Treat R_386_PLT32 relocation as R_386_PC32 Greg Kroah-Hartman
2021-03-05 12:22 ` [PATCH 4.9 30/41] Bluetooth: Fix null pointer dereference in amp_read_loc_assoc_final_data Greg Kroah-Hartman
2021-03-05 12:22 ` [PATCH 4.9 31/41] staging: most: sound: add sanity check for function argument Greg Kroah-Hartman
2021-03-05 12:22 ` [PATCH 4.9 32/41] media: uvcvideo: Allow entities with no pads Greg Kroah-Hartman
2021-03-05 12:22 ` [PATCH 4.9 33/41] scsi: iscsi: Restrict sessions and handles to admin capabilities Greg Kroah-Hartman
2021-03-05 12:22 ` [PATCH 4.9 34/41] sysfs: Add sysfs_emit and sysfs_emit_at to format sysfs output Greg Kroah-Hartman
2021-03-05 12:22 ` [PATCH 4.9 35/41] scsi: iscsi: Ensure sysfs attributes are limited to PAGE_SIZE Greg Kroah-Hartman
2021-03-05 12:22 ` [PATCH 4.9 36/41] scsi: iscsi: Verify lengths on passthrough PDUs Greg Kroah-Hartman
2021-03-05 12:22 ` [PATCH 4.9 37/41] Xen/gnttab: handle p2m update errors on a per-slot basis Greg Kroah-Hartman
2021-03-05 12:22 ` [PATCH 4.9 38/41] xen-netback: respect gnttab_map_refs()s return value Greg Kroah-Hartman
2021-03-05 12:22 ` [PATCH 4.9 39/41] zsmalloc: account the number of compacted pages correctly Greg Kroah-Hartman
2021-03-05 12:22 ` [PATCH 4.9 40/41] swap: fix swapfile read/write offset Greg Kroah-Hartman
2021-03-05 12:22 ` [PATCH 4.9 41/41] media: v4l: ioctl: Fix memory leak in video_usercopy Greg Kroah-Hartman
2021-03-06 5:16 ` [PATCH 4.9 00/41] 4.9.260-rc1 review Florian Fainelli
2021-03-06 16:29 ` Guenter Roeck
2021-03-06 16:30 ` Guenter Roeck
2021-03-07 2:26 ` Naresh Kamboju
2021-03-12 20:24 ` Florian Fainelli
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