From: "Luis Claudio R. Goncalves" <lclaudio@uudg.org>
Date: Tue, 25 Jun 2019 11:28:04 -0300
Subject: [PATCH] mm/zswap: Do not disable preemption in
zswap_frontswap_store()
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-rt-devel.git
Git-commit: da77ceac3d20f27310a07a7c346a4ee6b40d6c28
Patch-mainline: Queued in subsystem maintainer repository
References: SLE Realtime Extension
Zswap causes "BUG: scheduling while atomic" by blocking on a rt_spin_lock() with
preemption disabled. The preemption is disabled by get_cpu_var() in
zswap_frontswap_store() to protect the access of the zswap_dstmem percpu variable.
Use get_locked_var() to protect the percpu zswap_dstmem variable, making the
code preemptive.
As get_cpu_ptr() also disables preemption, replace it by this_cpu_ptr() and
remove the counterpart put_cpu_ptr().
Steps to Reproduce:
1. # grubby --args "zswap.enabled=1" --update-kernel DEFAULT
2. # reboot
3. Calculate the amount o memory to be used by the test:
---> grep MemAvailable /proc/meminfo
---> Add 25% ~ 50% to that value
4. # stress --vm 1 --vm-bytes ${MemAvailable+25%} --timeout 240s
Usually, in less than 5 minutes the backtrace listed below appears, followed
by a kernel panic:
| BUG: scheduling while atomic: kswapd1/181/0x00000002
|
| Preemption disabled at:
| [<ffffffff8b2a6cda>] zswap_frontswap_store+0x21a/0x6e1
|
| Kernel panic - not syncing: scheduling while atomic
| CPU: 14 PID: 181 Comm: kswapd1 Kdump: loaded Not tainted 5.0.14-rt9 #1
| Hardware name: AMD Pence/Pence, BIOS WPN2321X_Weekly_12_03_21 03/19/2012
| Call Trace:
| panic+0x106/0x2a7
| __schedule_bug.cold+0x3f/0x51
| __schedule+0x5cb/0x6f0
| schedule+0x43/0xd0
| rt_spin_lock_slowlock_locked+0x114/0x2b0
| rt_spin_lock_slowlock+0x51/0x80
| zbud_alloc+0x1da/0x2d0
| zswap_frontswap_store+0x31a/0x6e1
| __frontswap_store+0xab/0x130
| swap_writepage+0x39/0x70
| pageout.isra.0+0xe3/0x320
| shrink_page_list+0xa8e/0xd10
| shrink_inactive_list+0x251/0x840
| shrink_node_memcg+0x213/0x770
| shrink_node+0xd9/0x450
| balance_pgdat+0x2d5/0x510
| kswapd+0x218/0x470
| kthread+0xfb/0x130
| ret_from_fork+0x27/0x50
Cc: stable-rt@vger.kernel.org
Reported-by: Ping Fang <pifang@redhat.com>
Signed-off-by: Luis Claudio R. Goncalves <lgoncalv@redhat.com>
Reviewed-by: Daniel Bristot de Oliveira <bristot@redhat.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Daniel Wagner <dwagner@suse.de>
---
mm/zswap.c | 12 +++++++-----
1 file changed, 7 insertions(+), 5 deletions(-)
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -18,6 +18,7 @@
#include <linux/highmem.h>
#include <linux/slab.h>
#include <linux/spinlock.h>
+#include <linux/locallock.h>
#include <linux/types.h>
#include <linux/atomic.h>
#include <linux/frontswap.h>
@@ -980,6 +981,8 @@ static void zswap_fill_page(void *ptr, u
memset_l(page, value, PAGE_SIZE / sizeof(unsigned long));
}
+/* protect zswap_dstmem from concurrency */
+static DEFINE_LOCAL_IRQ_LOCK(zswap_dstmem_lock);
/*********************************
* frontswap hooks
**********************************/
@@ -1057,12 +1060,11 @@ static int zswap_frontswap_store(unsigne
}
/* compress */
- dst = get_cpu_var(zswap_dstmem);
- tfm = *get_cpu_ptr(entry->pool->tfm);
+ dst = get_locked_var(zswap_dstmem_lock, zswap_dstmem);
+ tfm = *this_cpu_ptr(entry->pool->tfm);
src = kmap_atomic(page);
ret = crypto_comp_compress(tfm, src, PAGE_SIZE, dst, &dlen);
kunmap_atomic(src);
- put_cpu_ptr(entry->pool->tfm);
if (ret) {
ret = -EINVAL;
goto put_dstmem;
@@ -1086,7 +1088,7 @@ static int zswap_frontswap_store(unsigne
memcpy(buf, &zhdr, hlen);
memcpy(buf + hlen, dst, dlen);
zpool_unmap_handle(entry->pool->zpool, handle);
- put_cpu_var(zswap_dstmem);
+ put_locked_var(zswap_dstmem_lock, zswap_dstmem);
/* populate entry */
entry->offset = offset;
@@ -1114,7 +1116,7 @@ static int zswap_frontswap_store(unsigne
return 0;
put_dstmem:
- put_cpu_var(zswap_dstmem);
+ put_locked_var(zswap_dstmem_lock, zswap_dstmem);
zswap_pool_put(entry->pool);
freepage:
zswap_entry_cache_free(entry);