From: "Luis Claudio R. Goncalves" Date: Tue, 25 Jun 2019 11:28:04 -0300 Subject: [PATCH 277/353] mm/zswap: Do not disable preemption in zswap_frontswap_store() Origin: https://git.kernel.org/cgit/linux/kernel/git/rt/linux-stable-rt.git/commit?id=76b124c411d62a490954f663e6408c62b0b5ae0c [ Upstream commit 4e4cf4be79635e67144632d9135286381acbc95a ] 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: | [] 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 Signed-off-by: Luis Claudio R. Goncalves Reviewed-by: Daniel Bristot de Oliveira Signed-off-by: Sebastian Andrzej Siewior Signed-off-by: Steven Rostedt (VMware) --- mm/zswap.c | 12 +++++++----- 1 file changed, 7 insertions(+), 5 deletions(-) diff --git a/mm/zswap.c b/mm/zswap.c index cd91fd9d96b8..420225d3ff0b 100644 --- a/mm/zswap.c +++ b/mm/zswap.c @@ -27,6 +27,7 @@ #include #include #include +#include #include #include #include @@ -990,6 +991,8 @@ static void zswap_fill_page(void *ptr, unsigned long value) memset_l(page, value, PAGE_SIZE / sizeof(unsigned long)); } +/* protect zswap_dstmem from concurrency */ +static DEFINE_LOCAL_IRQ_LOCK(zswap_dstmem_lock); /********************************* * frontswap hooks **********************************/ @@ -1066,12 +1069,11 @@ static int zswap_frontswap_store(unsigned type, pgoff_t offset, } /* 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; @@ -1094,7 +1096,7 @@ static int zswap_frontswap_store(unsigned type, pgoff_t offset, 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; @@ -1122,7 +1124,7 @@ static int zswap_frontswap_store(unsigned type, pgoff_t offset, 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);