mirrors/linux-stable
1
0
Fork 0
mirror of https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git synced 2024-10-30 08:02:30 +00:00
Code Issues Releases Wiki Activity

kvfree_rcu: Fix comments according to current code

Browse source 
The kvfree_rcu() function now defers allocations in the common
case due to the fact that there is no lockless access to the
memory-allocator caches/pools.  In addition, in CONFIG_PREEMPT_NONE=y
and in CONFIG_PREEMPT_VOLUNTARY=y kernels, there is no reliable way to
determine if spinlocks are held.  As a result, allocation is deferred in
the common case, and the two-argument form of kvfree_rcu() thus uses the
"channel 3" queue through all the rcu_head structures.  This channel
is called referred to as the emergency case in comments, and these
comments are now obsolete.

This commit therefore updates these comments to reflect the new
common-case nature of such emergencies.

Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Uladzislau Rezki (Sony) 2021-04-28 15:44:22 +02:00 committed by Paul E. McKenney
parent 7fe1da33f6
commit d8628f35ba
1 changed files with 9 additions and 6 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

15
kernel/rcu/tree.c
View file

@ -3355,9 +3355,11 @@ static void kfree_rcu_work(struct work_struct *work)
} }
/* /*
* Emergency case only. It can happen under low memory * This is used when the "bulk" path can not be used for the
* condition when an allocation gets failed, so the "bulk" * double-argument of kvfree_rcu(). This happens when the
* path can not be temporary maintained. * page-cache is empty, which means that objects are instead
* queued on a linked list through their rcu_head structures.
* This list is named "Channel 3".
*/ */
for (; head; head = next) { for (; head; head = next) {
unsigned long offset = (unsigned long)head->func; unsigned long offset = (unsigned long)head->func;
@ -3403,8 +3405,8 @@ static inline bool queue_kfree_rcu_work(struct kfree_rcu_cpu *krcp)
if ((krcp->bkvhead[0] && !krwp->bkvhead_free[0]) || if ((krcp->bkvhead[0] && !krwp->bkvhead_free[0]) ||
(krcp->bkvhead[1] && !krwp->bkvhead_free[1]) || (krcp->bkvhead[1] && !krwp->bkvhead_free[1]) ||
(krcp->head && !krwp->head_free)) { (krcp->head && !krwp->head_free)) {
// Channel 1 corresponds to SLAB ptrs. // Channel 1 corresponds to the SLAB-pointer bulk path.
// Channel 2 corresponds to vmalloc ptrs. // Channel 2 corresponds to vmalloc-pointer bulk path.
for (j = 0; j < FREE_N_CHANNELS; j++) { for (j = 0; j < FREE_N_CHANNELS; j++) {
if (!krwp->bkvhead_free[j]) { if (!krwp->bkvhead_free[j]) {
krwp->bkvhead_free[j] = krcp->bkvhead[j]; krwp->bkvhead_free[j] = krcp->bkvhead[j];
@ -3412,7 +3414,8 @@ static inline bool queue_kfree_rcu_work(struct kfree_rcu_cpu *krcp)
} }
} }
// Channel 3 corresponds to emergency path. // Channel 3 corresponds to both SLAB and vmalloc
// objects queued on the linked list.
if (!krwp->head_free) { if (!krwp->head_free) {
krwp->head_free = krcp->head; krwp->head_free = krcp->head;
krcp->head = NULL; krcp->head = NULL;