mm/zswap: Do not disable preemption in zswap_frontswap_store()
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>
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12
mm/zswap.c
12
mm/zswap.c
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@ -18,6 +18,7 @@
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#include <linux/highmem.h>
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#include <linux/slab.h>
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#include <linux/spinlock.h>
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#include <linux/locallock.h>
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#include <linux/types.h>
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#include <linux/atomic.h>
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#include <linux/frontswap.h>
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@ -980,6 +981,8 @@ static void zswap_fill_page(void *ptr, unsigned long value)
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memset_l(page, value, PAGE_SIZE / sizeof(unsigned long));
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}
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/* protect zswap_dstmem from concurrency */
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static DEFINE_LOCAL_IRQ_LOCK(zswap_dstmem_lock);
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/*********************************
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* frontswap hooks
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**********************************/
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@ -1057,12 +1060,11 @@ static int zswap_frontswap_store(unsigned type, pgoff_t offset,
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}
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/* compress */
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dst = get_cpu_var(zswap_dstmem);
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tfm = *get_cpu_ptr(entry->pool->tfm);
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dst = get_locked_var(zswap_dstmem_lock, zswap_dstmem);
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tfm = *this_cpu_ptr(entry->pool->tfm);
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src = kmap_atomic(page);
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ret = crypto_comp_compress(tfm, src, PAGE_SIZE, dst, &dlen);
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kunmap_atomic(src);
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put_cpu_ptr(entry->pool->tfm);
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if (ret) {
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ret = -EINVAL;
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goto put_dstmem;
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@ -1086,7 +1088,7 @@ static int zswap_frontswap_store(unsigned type, pgoff_t offset,
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memcpy(buf, &zhdr, hlen);
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memcpy(buf + hlen, dst, dlen);
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zpool_unmap_handle(entry->pool->zpool, handle);
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put_cpu_var(zswap_dstmem);
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put_locked_var(zswap_dstmem_lock, zswap_dstmem);
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/* populate entry */
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entry->offset = offset;
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@ -1114,7 +1116,7 @@ insert_entry:
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return 0;
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put_dstmem:
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put_cpu_var(zswap_dstmem);
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put_locked_var(zswap_dstmem_lock, zswap_dstmem);
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zswap_pool_put(entry->pool);
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freepage:
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zswap_entry_cache_free(entry);
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