From: Hou Tao houtao1@huawei.com

hulk inclusion category: bugfix bugzilla: 167067 CVE: NA

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In __blkdev_direct_IO_simple(), when bi_private is NULL, it assumes bi_css must be NULL as showed below:

CPU 1: CPU 2:

__blkdev_direct_IO_simple submit_bio

bio_endio bio_uninit(bio) css_put(bi_css) bi_css = NULL set_current_state(TASK_UNINTERRUPTIBLE) bio->bi_end_io blkdev_bio_end_io_simple bio->bi_private = NULL // bi_private is NULL READ_ONCE(bio->bi_private) wake_up_process smp_mb__after_spinlock

bio_unint(bio) // read bi_css as no-NULL css_put(bi_css)

Because there is no memory barrier between the reading and the writing of these two variables, the assumption is wrong under weak-memory model machine (e.g. arm64). bi_css will be put twice and leads to the following warning:

percpu_ref_switch_to_atomic_rcu: percpu ref (css_release) <= 0 (-3) after switching to atomic

There is a similar problem in __blkdev_direct_IO() which occurs between dio->waiter and bio.bi_status.

Fixing it by adding a smp_rmb() between the reads of two variables, and a corresponding smp_wmb() between the writes.

Signed-off-by: Hou Tao houtao1@huawei.com Signed-off-by: Yu Kuai yukuai3@huawei.com Reviewed-by: Jason Yan yanaijie@huawei.com Signed-off-by: Yang Yingliang yangyingliang@huawei.com --- fs/block_dev.c | 24 ++++++++++++++++++++++-- 1 file changed, 22 insertions(+), 2 deletions(-)

diff --git a/fs/block_dev.c b/fs/block_dev.c index 786d105692e85..30dd7b19bd2e3 100644 --- a/fs/block_dev.c +++ b/fs/block_dev.c @@ -195,6 +195,11 @@ static void blkdev_bio_end_io_simple(struct bio *bio) { struct task_struct *waiter = bio->bi_private;

+ /* + * Paired with smp_rmb() after reading bio->bi_private + * in __blkdev_direct_IO_simple() + */ + smp_wmb(); WRITE_ONCE(bio->bi_private, NULL); wake_up_process(waiter); } @@ -251,8 +256,14 @@ __blkdev_direct_IO_simple(struct kiocb *iocb, struct iov_iter *iter, qc = submit_bio(&bio); for (;;) { set_current_state(TASK_UNINTERRUPTIBLE); - if (!READ_ONCE(bio.bi_private)) + if (!READ_ONCE(bio.bi_private)) { + /* + * Paired with smp_wmb() in + * blkdev_bio_end_io_simple() + */ + smp_rmb(); break; + } if (!(iocb->ki_flags & IOCB_HIPRI) || !blk_poll(bdev_get_queue(bdev), qc)) io_schedule(); @@ -317,6 +328,12 @@ static void blkdev_bio_end_io(struct bio *bio) } else { struct task_struct *waiter = dio->waiter;

+ if (!dio->multi_bio) + /* + * Paired with smp_rmb() after reading + * dio->waiter in __blkdev_direct_IO() + */ + smp_wmb(); WRITE_ONCE(dio->waiter, NULL); wake_up_process(waiter); } @@ -417,8 +434,11 @@ __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter, int nr_pages)

for (;;) { set_current_state(TASK_UNINTERRUPTIBLE); - if (!READ_ONCE(dio->waiter)) + if (!READ_ONCE(dio->waiter)) { + /* Paired with smp_wmb() in blkdev_bio_end_io() */ + smp_rmb(); break; + }

if (!(iocb->ki_flags & IOCB_HIPRI) || !blk_poll(bdev_get_queue(bdev), qc))