Patch "blk-cgroup: Fix the recursive blkg rwstat" has been added to the 5.11-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    blk-cgroup: Fix the recursive blkg rwstat

to the 5.11-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     blk-cgroup-fix-the-recursive-blkg-rwstat.patch
and it can be found in the queue-5.11 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 128922884b3598bd8021f22fd0cf9fec17dd427f
Author: Xunlei Pang <xlpang@xxxxxxxxxxxxxxxxx>
Date:   Fri Mar 5 16:13:27 2021 +0800

    blk-cgroup: Fix the recursive blkg rwstat
    
    [ Upstream commit 4f44657d74873735e93a50eb25014721a66aac19 ]
    
    The current blkio.throttle.io_service_bytes_recursive doesn't
    work correctly.
    
    As an example, for the following blkcg hierarchy:
     (Made 1GB READ in test1, 512MB READ in test2)
         test
        /    \
     test1   test2
    
    $ head -n 1 test/test1/blkio.throttle.io_service_bytes_recursive
    8:0 Read 1073684480
    $ head -n 1 test/test2/blkio.throttle.io_service_bytes_recursive
    8:0 Read 537448448
    $ head -n 1 test/blkio.throttle.io_service_bytes_recursive
    8:0 Read 537448448
    
    Clearly, above data of "test" reflects "test2" not "test1"+"test2".
    
    Do the correct summary in blkg_rwstat_recursive_sum().
    
    Signed-off-by: Xunlei Pang <xlpang@xxxxxxxxxxxxxxxxx>
    Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/block/blk-cgroup-rwstat.c b/block/blk-cgroup-rwstat.c
index 85d5790ac49b..3304e841df7c 100644
--- a/block/blk-cgroup-rwstat.c
+++ b/block/blk-cgroup-rwstat.c
@@ -109,6 +109,7 @@ void blkg_rwstat_recursive_sum(struct blkcg_gq *blkg, struct blkcg_policy *pol,
 
 	lockdep_assert_held(&blkg->q->queue_lock);
 
+	memset(sum, 0, sizeof(*sum));
 	rcu_read_lock();
 	blkg_for_each_descendant_pre(pos_blkg, pos_css, blkg) {
 		struct blkg_rwstat *rwstat;
@@ -122,7 +123,7 @@ void blkg_rwstat_recursive_sum(struct blkcg_gq *blkg, struct blkcg_policy *pol,
 			rwstat = (void *)pos_blkg + off;
 
 		for (i = 0; i < BLKG_RWSTAT_NR; i++)
-			sum->cnt[i] = blkg_rwstat_read_counter(rwstat, i);
+			sum->cnt[i] += blkg_rwstat_read_counter(rwstat, i);
 	}
 	rcu_read_unlock();
 }