linux-kernel - [PATCH 4.9 013/120] zram: revalidate disk under init

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Message-Id: <20170118104648.673741701@linuxfoundation.org>
Date:   Wed, 18 Jan 2017 11:45:31 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Minchan Kim <minchan@...nel.org>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Takashi Iwai <tiwai@...e.de>,
        Hyeoncheol Lee <cheol.lee@....com>, yjay.kim@....com,
        Sangseok Lee <sangseok.lee@....com>,
        Hugh Dickins <hughd@...gle.com>,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH 4.9 013/120] zram: revalidate disk under init_lock

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Minchan Kim <minchan@...nel.org>

commit e7ccfc4ccb703e0f033bd4617580039898e912dd upstream.

Commit b4c5c60920e3 ("zram: avoid lockdep splat by revalidate_disk")
moved revalidate_disk call out of init_lock to avoid lockdep
false-positive splat.  However, commit 08eee69fcf6b ("zram: remove
init_lock in zram_make_request") removed init_lock in IO path so there
is no worry about lockdep splat.  So, let's restore it.

This patch is needed to set BDI_CAP_STABLE_WRITES atomically in next
patch.

Fixes: da9556a2367c ("zram: user per-cpu compression streams")
Link: http://lkml.kernel.org/r/1482366980-3782-3-git-send-email-minchan@kernel.org
Signed-off-by: Minchan Kim <minchan@...nel.org>
Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Cc: Takashi Iwai <tiwai@...e.de>
Cc: Hyeoncheol Lee <cheol.lee@....com>
Cc: <yjay.kim@....com>
Cc: Sangseok Lee <sangseok.lee@....com>
Cc: Hugh Dickins <hughd@...gle.com>
Cc: Darrick J. Wong <darrick.wong@...cle.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/block/zram/zram_drv.c |    8 +-------
 1 file changed, 1 insertion(+), 7 deletions(-)

--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -1094,14 +1094,8 @@ static ssize_t disksize_store(struct dev
 	zram->comp = comp;
 	zram->disksize = disksize;
 	set_capacity(zram->disk, zram->disksize >> SECTOR_SHIFT);
-	up_write(&zram->init_lock);
-
-	/*
-	 * Revalidate disk out of the init_lock to avoid lockdep splat.
-	 * It's okay because disk's capacity is protected by init_lock
-	 * so that revalidate_disk always sees up-to-date capacity.
-	 */
 	revalidate_disk(zram->disk);
+	up_write(&zram->init_lock);

 	return len;