From: "Luis Claudio R. Goncalves" <[email protected]> zwap uses per-CPU compression. The per-CPU data pointer is acquired with get_cpu_ptr() which implicitly disables preemption. It allocates memory inside the preempt disabled region which conflicts with the PREEMPT_RT semantics.
Replace the implicit preemption control with an explicit local lock. This allows RT kernels to substitute it with a real per CPU lock, which serializes the access but keeps the code section preemptible. On non RT kernels this maps to preempt_disable() as before, i.e. no functional change. [bigeasy: Use local_lock(), additional hunks, patch description] Cc: Seth Jennings <[email protected]> Cc: Dan Streetman <[email protected]> Cc: Vitaly Wool <[email protected]> Cc: Andrew Morton <[email protected]> Cc: [email protected] Signed-off-by: Luis Claudio R. Goncalves <[email protected]> Signed-off-by: Sebastian Andrzej Siewior <[email protected]> --- mm/zswap.c | 23 ++++++++++++++--------- 1 file changed, 14 insertions(+), 9 deletions(-) diff --git a/mm/zswap.c b/mm/zswap.c index fbb782924ccc5..1db2ad941e501 100644 --- 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> @@ -388,6 +389,8 @@ static struct zswap_entry *zswap_entry_find_get(struct rb_root *root, * per-cpu code **********************************/ static DEFINE_PER_CPU(u8 *, zswap_dstmem); +/* Used for zswap_dstmem and tfm */ +static DEFINE_LOCAL_LOCK(zswap_cpu_lock); static int zswap_dstmem_prepare(unsigned int cpu) { @@ -919,10 +922,11 @@ static int zswap_writeback_entry(struct zpool *pool, unsigned long handle) dlen = PAGE_SIZE; src = (u8 *)zhdr + sizeof(struct zswap_header); dst = kmap_atomic(page); - tfm = *get_cpu_ptr(entry->pool->tfm); + local_lock(zswap_cpu_lock); + tfm = *this_cpu_ptr(entry->pool->tfm); ret = crypto_comp_decompress(tfm, src, entry->length, dst, &dlen); - put_cpu_ptr(entry->pool->tfm); + local_unlock(zswap_cpu_lock); kunmap_atomic(dst); BUG_ON(ret); BUG_ON(dlen != PAGE_SIZE); @@ -1074,12 +1078,12 @@ static int zswap_frontswap_store(unsigned type, pgoff_t offset, } /* compress */ - dst = get_cpu_var(zswap_dstmem); - tfm = *get_cpu_ptr(entry->pool->tfm); + local_lock(zswap_cpu_lock); + dst = *this_cpu_ptr(&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; @@ -1103,7 +1107,7 @@ 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); + local_unlock(zswap_cpu_lock); /* populate entry */ entry->offset = offset; @@ -1131,7 +1135,7 @@ static int zswap_frontswap_store(unsigned type, pgoff_t offset, return 0; put_dstmem: - put_cpu_var(zswap_dstmem); + local_unlock(zswap_cpu_lock); zswap_pool_put(entry->pool); freepage: zswap_entry_cache_free(entry); @@ -1176,9 +1180,10 @@ static int zswap_frontswap_load(unsigned type, pgoff_t offset, if (zpool_evictable(entry->pool->zpool)) src += sizeof(struct zswap_header); dst = kmap_atomic(page); - tfm = *get_cpu_ptr(entry->pool->tfm); + local_lock(zswap_cpu_lock); + tfm = *this_cpu_ptr(entry->pool->tfm); ret = crypto_comp_decompress(tfm, src, entry->length, dst, &dlen); - put_cpu_ptr(entry->pool->tfm); + local_unlock(zswap_cpu_lock); kunmap_atomic(dst); zpool_unmap_handle(entry->pool->zpool, entry->handle); BUG_ON(ret); -- 2.26.2
