diff mbox series

zram: Fix __zram_bvec_{read,write}() locking order

Message ID 20201019101353.GJ2628@hirez.programming.kicks-ass.net (mailing list archive)
State New, archived
Headers show
Series zram: Fix __zram_bvec_{read,write}() locking order | expand

Commit Message

Peter Zijlstra Oct. 19, 2020, 10:13 a.m. UTC 
Mikhail reported a lockdep spat detailing how __zram_bvec_read() and
__zram_bvec_write() use zstrm->lock and zspage->lock in opposite order.

Reported-by: Mikhail Gavrilov <mikhail.v.gavrilov@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Mikhail Gavrilov <mikhail.v.gavrilov@gmail.com>
---
 drivers/block/zram/zram_drv.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

Comments

Minchan Kim Oct. 19, 2020, 2:08 p.m. UTC | #1 
On Mon, Oct 19, 2020 at 12:13:53PM +0200, Peter Zijlstra wrote:
> 
> Mikhail reported a lockdep spat detailing how __zram_bvec_read() and
> __zram_bvec_write() use zstrm->lock and zspage->lock in opposite order.
> 
> Reported-by: Mikhail Gavrilov <mikhail.v.gavrilov@gmail.com>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> Tested-by: Mikhail Gavrilov <mikhail.v.gavrilov@gmail.com>
Acked-by: Minchan Kim <minchan@kernel.org>

Thanks for the fix.
Sebastian Andrzej Siewior Oct. 19, 2020, 3:29 p.m. UTC | #2 
On 2020-10-19 12:13:53 [+0200], Peter Zijlstra wrote:
> 
> Mikhail reported a lockdep spat detailing how __zram_bvec_read() and
> __zram_bvec_write() use zstrm->lock and zspage->lock in opposite order.
> 
> Reported-by: Mikhail Gavrilov <mikhail.v.gavrilov@gmail.com>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> Tested-by: Mikhail Gavrilov <mikhail.v.gavrilov@gmail.com>

We have the same patch in RT. I didn't submit it with the other
local-lock patches because this splat pops up once pin_tag() is made a
sleeping lock. I missed the part where migrate_read_lock() can be a
lock. So:

Acked-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

Sebastian
Jens Axboe Oct. 19, 2020, 3:32 p.m. UTC | #3 
On 10/19/20 4:13 AM, Peter Zijlstra wrote:
> 
> Mikhail reported a lockdep spat detailing how __zram_bvec_read() and
> __zram_bvec_write() use zstrm->lock and zspage->lock in opposite order.

Applied, thanks.
diff mbox series

Patch

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 9100ac36670a..c1e2c2e1cde8 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -1216,10 +1216,11 @@  static void zram_free_page(struct zram *zram, size_t index)
 static int __zram_bvec_read(struct zram *zram, struct page *page, u32 index,
 				struct bio *bio, bool partial_io)
 {
-	int ret;
+	struct zcomp_strm *zstrm;
 	unsigned long handle;
 	unsigned int size;
 	void *src, *dst;
+	int ret;
 
 	zram_slot_lock(zram, index);
 	if (zram_test_flag(zram, index, ZRAM_WB)) {
@@ -1250,6 +1251,9 @@  static int __zram_bvec_read(struct zram *zram, struct page *page, u32 index,
 
 	size = zram_get_obj_size(zram, index);
 
+	if (size != PAGE_SIZE)
+		zstrm = zcomp_stream_get(zram->comp);
+
 	src = zs_map_object(zram->mem_pool, handle, ZS_MM_RO);
 	if (size == PAGE_SIZE) {
 		dst = kmap_atomic(page);
@@ -1257,8 +1261,6 @@  static int __zram_bvec_read(struct zram *zram, struct page *page, u32 index,
 		kunmap_atomic(dst);
 		ret = 0;
 	} else {
-		struct zcomp_strm *zstrm = zcomp_stream_get(zram->comp);
-
 		dst = kmap_atomic(page);
 		ret = zcomp_decompress(zstrm, src, size, dst);
 		kunmap_atomic(dst);