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From: Peter Zijlstra <peterz@infradead.org>
To: Minchan Kim <minchan@kernel.org>
Cc: Mikhail Gavrilov <mikhail.v.gavrilov@gmail.com>,
	Linux List Kernel Mailing <linux-kernel@vger.kernel.org>,
	linux-block@vger.kernel.org,
	Mike Galbraith <umgwanakikbuti@gmail.com>,
	ngupta@vflare.org, sergey.senozhatsky.work@gmail.com,
	bigeasy@linutronix.de, Andrew Morton <akpm@linux-foundation.org>
Subject: [PATCH] zram: Fix __zram_bvec_{read,write}() locking order
Date: Mon, 19 Oct 2020 12:13:53 +0200	[thread overview]
Message-ID: <20201019101353.GJ2628@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20201016153324.GA1976566@google.com>


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(-)

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);

  reply	other threads:[~2020-10-19 10:14 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-16  6:21 swapon/913 is trying to acquire lock at zcomp_stream_get+0x5/0x90 [zram] but task is already holding lock at zs_map_object+0x7a/0x2e0 Mikhail Gavrilov
2020-10-16 12:40 ` Peter Zijlstra
2020-10-16 14:00   ` Mikhail Gavrilov
2020-10-16 15:33   ` Minchan Kim
2020-10-19 10:13     ` Peter Zijlstra [this message]
2020-10-19 14:08       ` [PATCH] zram: Fix __zram_bvec_{read,write}() locking order Minchan Kim
2020-10-19 15:29       ` Sebastian Andrzej Siewior
2020-10-19 15:32       ` Jens Axboe

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