From ba6b17d68c8e3aa8d55d0474299cb931965c5ea5 Mon Sep 17 00:00:00 2001 From: Sergey Senozhatsky Date: Thu, 12 Feb 2015 15:00:36 -0800 Subject: [PATCH] zram: fix umount-reset_store-mount race condition Ganesh Mahendran was the first one who proposed to use bdev->bd_mutex to avoid ->bd_holders race condition: CPU0 CPU1 umount /* zram->init_done is true */ reset_store() bdev->bd_holders == 0 mount ... zram_make_request() zram_reset_device() However, his solution required some considerable amount of code movement, which we can avoid. Apart from using bdev->bd_mutex in reset_store(), this patch also simplifies zram_reset_device(). zram_reset_device() has a bool parameter reset_capacity which tells it whether disk capacity and itself disk should be reset. There are two zram_reset_device() callers: -- zram_exit() passes reset_capacity=false -- reset_store() passes reset_capacity=true So we can move reset_capacity-sensitive work out of zram_reset_device() and perform it unconditionally in reset_store(). This also lets us drop reset_capacity parameter from zram_reset_device() and pass zram pointer only. Signed-off-by: Sergey Senozhatsky Reported-by: Ganesh Mahendran Cc: Minchan Kim Cc: Vlastimil Babka Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- drivers/block/zram/zram_drv.c | 23 +++++++++-------------- 1 file changed, 9 insertions(+), 14 deletions(-) diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c index 0e07652cf7c1..2607bd9f4955 100644 --- a/drivers/block/zram/zram_drv.c +++ b/drivers/block/zram/zram_drv.c @@ -715,7 +715,7 @@ static void zram_bio_discard(struct zram *zram, u32 index, } } -static void zram_reset_device(struct zram *zram, bool reset_capacity) +static void zram_reset_device(struct zram *zram) { down_write(&zram->init_lock); @@ -734,18 +734,7 @@ static void zram_reset_device(struct zram *zram, bool reset_capacity) memset(&zram->stats, 0, sizeof(zram->stats)); zram->disksize = 0; - if (reset_capacity) - set_capacity(zram->disk, 0); - 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. - */ - if (reset_capacity) - revalidate_disk(zram->disk); } static ssize_t disksize_store(struct device *dev, @@ -818,6 +807,7 @@ static ssize_t reset_store(struct device *dev, if (!bdev) return -ENOMEM; + mutex_lock(&bdev->bd_mutex); /* Do not reset an active device! */ if (bdev->bd_holders) { ret = -EBUSY; @@ -835,12 +825,17 @@ static ssize_t reset_store(struct device *dev, /* Make sure all pending I/O is finished */ fsync_bdev(bdev); + zram_reset_device(zram); + set_capacity(zram->disk, 0); + + mutex_unlock(&bdev->bd_mutex); + revalidate_disk(zram->disk); bdput(bdev); - zram_reset_device(zram, true); return len; out: + mutex_unlock(&bdev->bd_mutex); bdput(bdev); return ret; } @@ -1186,7 +1181,7 @@ static void __exit zram_exit(void) * Shouldn't access zram->disk after destroy_device * because destroy_device already released zram->disk. */ - zram_reset_device(zram, false); + zram_reset_device(zram); } unregister_blkdev(zram_major, "zram"); -- 2.20.1