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Message-Id: <20220715113349.831370-2-bfoster@redhat.com>
Date: Fri, 15 Jul 2022 07:33:47 -0400
From: Brian Foster <bfoster@...hat.com>
To: linux-kernel@...r.kernel.org, linux-mm@...ck.org
Cc: Matthew Wilcox <willy@...radead.org>, ikent@...hat.com,
oleg@...hat.com
Subject: [PATCH 1/3] pid: replace pidmap_lock with xarray lock
As a first step to changing the struct pid tracking code from the
idr over to the xarray, replace the custom pidmap_lock spinlock with
the internal lock associated with the underlying xarray. This is
effectively equivalent to using idr_lock() and friends, but since
the goal is to disentangle from the idr, move directly to the
underlying xarray api.
Signed-off-by: Matthew Wilcox <willy@...radead.org>
Signed-off-by: Brian Foster <bfoster@...hat.com>
---
kernel/pid.c | 79 ++++++++++++++++++++++++++--------------------------
1 file changed, 40 insertions(+), 39 deletions(-)
diff --git a/kernel/pid.c b/kernel/pid.c
index 2fc0a16ec77b..72a6e9d0db81 100644
--- a/kernel/pid.c
+++ b/kernel/pid.c
@@ -86,22 +86,6 @@ struct pid_namespace init_pid_ns = {
};
EXPORT_SYMBOL_GPL(init_pid_ns);
-/*
- * Note: disable interrupts while the pidmap_lock is held as an
- * interrupt might come in and do read_lock(&tasklist_lock).
- *
- * If we don't disable interrupts there is a nasty deadlock between
- * detach_pid()->free_pid() and another cpu that does
- * spin_lock(&pidmap_lock) followed by an interrupt routine that does
- * read_lock(&tasklist_lock);
- *
- * After we clean up the tasklist_lock and know there are no
- * irq handlers that take it we can leave the interrupts enabled.
- * For now it is easier to be safe than to prove it can't happen.
- */
-
-static __cacheline_aligned_in_smp DEFINE_SPINLOCK(pidmap_lock);
-
void put_pid(struct pid *pid)
{
struct pid_namespace *ns;
@@ -129,10 +113,11 @@ void free_pid(struct pid *pid)
int i;
unsigned long flags;
- spin_lock_irqsave(&pidmap_lock, flags);
for (i = 0; i <= pid->level; i++) {
struct upid *upid = pid->numbers + i;
struct pid_namespace *ns = upid->ns;
+
+ xa_lock_irqsave(&ns->idr.idr_rt, flags);
switch (--ns->pid_allocated) {
case 2:
case 1:
@@ -150,8 +135,8 @@ void free_pid(struct pid *pid)
}
idr_remove(&ns->idr, upid->nr);
+ xa_unlock_irqrestore(&ns->idr.idr_rt, flags);
}
- spin_unlock_irqrestore(&pidmap_lock, flags);
call_rcu(&pid->rcu, delayed_put_pid);
}
@@ -206,7 +191,7 @@ struct pid *alloc_pid(struct pid_namespace *ns, pid_t *set_tid,
}
idr_preload(GFP_KERNEL);
- spin_lock_irq(&pidmap_lock);
+ xa_lock_irq(&tmp->idr.idr_rt);
if (tid) {
nr = idr_alloc(&tmp->idr, NULL, tid,
@@ -233,7 +218,7 @@ struct pid *alloc_pid(struct pid_namespace *ns, pid_t *set_tid,
nr = idr_alloc_cyclic(&tmp->idr, NULL, pid_min,
pid_max, GFP_ATOMIC);
}
- spin_unlock_irq(&pidmap_lock);
+ xa_unlock_irq(&tmp->idr.idr_rt);
idr_preload_end();
if (nr < 0) {
@@ -266,34 +251,38 @@ struct pid *alloc_pid(struct pid_namespace *ns, pid_t *set_tid,
INIT_HLIST_HEAD(&pid->inodes);
upid = pid->numbers + ns->level;
- spin_lock_irq(&pidmap_lock);
- if (!(ns->pid_allocated & PIDNS_ADDING))
- goto out_unlock;
for ( ; upid >= pid->numbers; --upid) {
+ tmp = upid->ns;
+
+ xa_lock_irq(&tmp->idr.idr_rt);
+ if (tmp == ns && !(tmp->pid_allocated & PIDNS_ADDING)) {
+ xa_unlock_irq(&tmp->idr.idr_rt);
+ put_pid_ns(ns);
+ goto out_free;
+ }
+
/* Make the PID visible to find_pid_ns. */
- idr_replace(&upid->ns->idr, pid, upid->nr);
- upid->ns->pid_allocated++;
+ idr_replace(&tmp->idr, pid, upid->nr);
+ tmp->pid_allocated++;
+ xa_unlock_irq(&tmp->idr.idr_rt);
}
- spin_unlock_irq(&pidmap_lock);
return pid;
-out_unlock:
- spin_unlock_irq(&pidmap_lock);
- put_pid_ns(ns);
-
out_free:
- spin_lock_irq(&pidmap_lock);
while (++i <= ns->level) {
upid = pid->numbers + i;
- idr_remove(&upid->ns->idr, upid->nr);
- }
+ tmp = upid->ns;
- /* On failure to allocate the first pid, reset the state */
- if (ns->pid_allocated == PIDNS_ADDING)
- idr_set_cursor(&ns->idr, 0);
+ xa_lock_irq(&tmp->idr.idr_rt);
- spin_unlock_irq(&pidmap_lock);
+ /* On failure to allocate the first pid, reset the state */
+ if (tmp == ns && tmp->pid_allocated == PIDNS_ADDING)
+ idr_set_cursor(&ns->idr, 0);
+
+ idr_remove(&tmp->idr, upid->nr);
+ xa_unlock_irq(&tmp->idr.idr_rt);
+ }
kmem_cache_free(ns->pid_cachep, pid);
return ERR_PTR(retval);
@@ -301,9 +290,9 @@ struct pid *alloc_pid(struct pid_namespace *ns, pid_t *set_tid,
void disable_pid_allocation(struct pid_namespace *ns)
{
- spin_lock_irq(&pidmap_lock);
+ xa_lock_irq(&ns->idr.idr_rt);
ns->pid_allocated &= ~PIDNS_ADDING;
- spin_unlock_irq(&pidmap_lock);
+ xa_unlock_irq(&ns->idr.idr_rt);
}
struct pid *find_pid_ns(int nr, struct pid_namespace *ns)
@@ -646,6 +635,18 @@ SYSCALL_DEFINE2(pidfd_open, pid_t, pid, unsigned int, flags)
return fd;
}
+/*
+ * Note: disable interrupts while the xarray lock is held as an interrupt might
+ * come in and do read_lock(&tasklist_lock).
+ *
+ * If we don't disable interrupts there is a nasty deadlock between
+ * detach_pid()->free_pid() and another cpu that does xa_lock() followed by an
+ * interrupt routine that does read_lock(&tasklist_lock);
+ *
+ * After we clean up the tasklist_lock and know there are no irq handlers that
+ * take it we can leave the interrupts enabled. For now it is easier to be safe
+ * than to prove it can't happen.
+ */
void __init pid_idr_init(void)
{
/* Verify no one has done anything silly: */
--
2.35.3
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