mm/zswap: add the flag can_sleep_mapped

Patch series "Fix the compatibility of zsmalloc and zswap".

Patch #1 adds a flag to zpool, then zswap used to determine if zpool
drivers such as zbud/z3fold/zsmalloc will enter an atomic context after
mapping.

The difference between zbud/z3fold and zsmalloc is that zsmalloc requires
an atomic context that since its map function holds a preempt-disabled,
but zbud/z3fold don't require an atomic context.  So patch #2 sets flag
sleep_mapped to true indicating that zbud/z3fold can sleep after mapping.
zsmalloc didn't support sleep after mapping, so don't set that flag to
true.

This patch (of 2):

Add a flag to zpool, named is "can_sleep_mapped", and have it set true for
zbud/z3fold, not set this flag for zsmalloc, so its default value is
false.  Then zswap could go the current path if the flag is true; and if
it's false, copy data from src to a temporary buffer, then unmap the
handle, take the mutex, process the buffer instead of src to avoid
sleeping function called from atomic context.

[[email protected]: add return value in zswap_frontswap_load]
  Link: https://lkml.kernel.org/r/[email protected]
[[email protected]: fix potential memory leak]
  Link: https://lkml.kernel.org/r/[email protected]
[[email protected]: fix potential uninitialized pointer read on tmp]
  Link: https://lkml.kernel.org/r/[email protected]
[[email protected]: fix variable 'entry' is uninitialized when used]
  Link: https://lkml.kernel.org/r/[email protected]: https://lkml.kernel.org/r/[email protected]

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Tian Tao <[email protected]>
Signed-off-by: Nathan Chancellor <[email protected]>
Signed-off-by: Colin Ian King <[email protected]>
Reviewed-by: Vitaly Wool <[email protected]>
Acked-by: Sebastian Andrzej Siewior <[email protected]>
Reported-by: Mike Galbraith <[email protected]>
Cc: Barry Song <[email protected]>
Cc: Dan Streetman <[email protected]>
Cc: Seth Jennings <[email protected]>
Cc: Dan Carpenter <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

1 files changed, 3 insertions, 0 deletions

diff --git a/include/linux/zpool.h b/include/linux/zpool.h
index 51bf43076165..e8997010612a 100644
--- a/include/linux/zpool.h
+++ b/include/linux/zpool.h
@@ -73,6 +73,7 @@ u64 zpool_get_total_size(struct zpool *pool);
  * @malloc:	allocate mem from a pool.
  * @free:	free mem from a pool.
  * @shrink:	shrink the pool.
+ * @sleep_mapped: whether zpool driver can sleep during map.
  * @map:	map a handle.
  * @unmap:	unmap a handle.
  * @total_size:	get total size of a pool.
@@ -100,6 +101,7 @@ struct zpool_driver {
 	int (*shrink)(void *pool, unsigned int pages,
 				unsigned int *reclaimed);
 
+	bool sleep_mapped;
 	void *(*map)(void *pool, unsigned long handle,
 				enum zpool_mapmode mm);
 	void (*unmap)(void *pool, unsigned long handle);
@@ -112,5 +114,6 @@ void zpool_register_driver(struct zpool_driver *driver);
 int zpool_unregister_driver(struct zpool_driver *driver);
 
 bool zpool_evictable(struct zpool *pool);
+bool zpool_can_sleep_mapped(struct zpool *pool);
 
 #endif