zram: remove init_lock in zram_make_request

Admin could reset zram during I/O operation going on so we have used
zram->init_lock as read-side lock in I/O path to prevent sudden zram
meta freeing.

However, the init_lock is really troublesome.  We can't do call
zram_meta_alloc under init_lock due to lockdep splat because
zram_rw_page is one of the function under reclaim path and hold it as
read_lock while other places in process context hold it as write_lock.
So, we have used allocation out of the lock to avoid lockdep warn but
it's not good for readability and fainally, I met another lockdep splat
between init_lock and cpu_hotplug from kmem_cache_destroy during working
zsmalloc compaction.  :(

Yes, the ideal is to remove horrible init_lock of zram in rw path.  This
patch removes it in rw path and instead, add atomic refcount for meta
lifetime management and completion to free meta in process context.
It's important to free meta in process context because some of resource
destruction needs mutex lock, which could be held if we releases the
resource in reclaim context so it's deadlock, again.

As a bonus, we could remove init_done check in rw path because
zram_meta_get will do a role for it, instead.

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Minchan Kim <minchan@kernel.org>
Cc: Nitin Gupta <ngupta@vflare.org>
Cc: Jerome Marchand <jmarchan@redhat.com>
Cc: Ganesh Mahendran <opensource.ganesh@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 11 insertions, 9 deletions

diff --git a/drivers/block/zram/zram_drv.h b/drivers/block/zram/zram_drv.h
index b05a816b09ac..5249f51ccdb3 100644
--- a/drivers/block/zram/zram_drv.h
+++ b/drivers/block/zram/zram_drv.h
@@ -100,24 +100,26 @@ struct zram_meta {
 
 struct zram {
 	struct zram_meta *meta;
+	struct zcomp *comp;
 	struct request_queue *queue;
 	struct gendisk *disk;
-	struct zcomp *comp;
-
-	/* Prevent concurrent execution of device init, reset and R/W request */
+	/* Prevent concurrent execution of device init */
 	struct rw_semaphore init_lock;
 	/*
-	 * This is the limit on amount of *uncompressed* worth of data
-	 * we can store in a disk.
+	 * the number of pages zram can consume for storing compressed data
 	 */
-	u64 disksize;	/* bytes */
+	unsigned long limit_pages;
 	int max_comp_streams;
+
 	struct zram_stats stats;
+	atomic_t refcount; /* refcount for zram_meta */
+	/* wait all IO under all of cpu are done */
+	wait_queue_head_t io_done;
 	/*
-	 * the number of pages zram can consume for storing compressed data
+	 * This is the limit on amount of *uncompressed* worth of data
+	 * we can store in a disk.
 	 */
-	unsigned long limit_pages;
-
+	u64 disksize;	/* bytes */
 	char compressor[10];
 };
 #endif