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[PATCH v2 2/7] bfq: protect q->blkg_list iteration in bfq_end_wr_async() with blkcg_mutex

Yu Kuai posted 7 patches 6 days, 12 hours ago
[PATCH v2 2/7] bfq: protect q->blkg_list iteration in bfq_end_wr_async() with blkcg_mutex
Posted by Yu Kuai 6 days, 12 hours ago 
bfq_end_wr_async() iterates q->blkg_list while only holding bfqd->lock,
but not blkcg_mutex. This can race with blkg_free_workfn() that removes
blkgs from the list while holding blkcg_mutex.

Add blkcg_mutex protection in bfq_end_wr() before taking bfqd->lock to
ensure proper synchronization when iterating q->blkg_list.

Signed-off-by: Yu Kuai <yukuai@fnnas.com>
---
 block/bfq-cgroup.c  | 3 ++-
 block/bfq-iosched.c | 2 ++
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/block/bfq-cgroup.c b/block/bfq-cgroup.c
index 6a75fe1c7a5c..839d266a6aa6 100644
--- a/block/bfq-cgroup.c
+++ b/block/bfq-cgroup.c
@@ -940,7 +940,8 @@ void bfq_end_wr_async(struct bfq_data *bfqd)
 	list_for_each_entry(blkg, &bfqd->queue->blkg_list, q_node) {
 		struct bfq_group *bfqg = blkg_to_bfqg(blkg);
 
-		bfq_end_wr_async_queues(bfqd, bfqg);
+		if (bfqg)
+			bfq_end_wr_async_queues(bfqd, bfqg);
 	}
 	bfq_end_wr_async_queues(bfqd, bfqd->root_group);
 }
diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index 3ebdec40e758..617633be8abc 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -2645,6 +2645,7 @@ static void bfq_end_wr(struct bfq_data *bfqd)
 	struct bfq_queue *bfqq;
 	int i;
 
+	mutex_lock(&bfqd->queue->blkcg_mutex);
 	spin_lock_irq(&bfqd->lock);
 
 	for (i = 0; i < bfqd->num_actuators; i++) {
@@ -2656,6 +2657,7 @@ static void bfq_end_wr(struct bfq_data *bfqd)
 	bfq_end_wr_async(bfqd);
 
 	spin_unlock_irq(&bfqd->lock);
+	mutex_unlock(&bfqd->queue->blkcg_mutex);
 }
 
 static sector_t bfq_io_struct_pos(void *io_struct, bool request)
-- 
2.51.0
Re: [PATCH v2 2/7] bfq: protect q->blkg_list iteration in bfq_end_wr_async() with blkcg_mutex
Posted by kernel test robot 6 days, 6 hours ago 
Hi Yu,

kernel test robot noticed the following build errors:

[auto build test ERROR on axboe/for-next]
[also build test ERROR on linus/master v6.19-rc8 next-20260202]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Yu-Kuai/blk-cgroup-protect-q-blkg_list-iteration-in-blkg_destroy_all-with-blkcg_mutex/20260203-161356
base:   https://git.kernel.org/pub/scm/linux/kernel/git/axboe/linux.git for-next
patch link:    https://lore.kernel.org/r/20260203080602.726505-3-yukuai%40fnnas.com
patch subject: [PATCH v2 2/7] bfq: protect q->blkg_list iteration in bfq_end_wr_async() with blkcg_mutex
config: s390-randconfig-002-20260203 (https://download.01.org/0day-ci/archive/20260203/202602032109.oYgANNeZ-lkp@intel.com/config)
compiler: clang version 22.0.0git (https://github.com/llvm/llvm-project 9b8addffa70cee5b2acc5454712d9cf78ce45710)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260203/202602032109.oYgANNeZ-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202602032109.oYgANNeZ-lkp@intel.com/

All errors (new ones prefixed by >>):

>> block/bfq-iosched.c:2648:27: error: no member named 'blkcg_mutex' in 'struct request_queue'
    2648 |         mutex_lock(&bfqd->queue->blkcg_mutex);
         |                     ~~~~~~~~~~~  ^
   include/linux/mutex.h:193:44: note: expanded from macro 'mutex_lock'
     193 | #define mutex_lock(lock) mutex_lock_nested(lock, 0)
         |                                            ^~~~
   block/bfq-iosched.c:2660:29: error: no member named 'blkcg_mutex' in 'struct request_queue'
    2660 |         mutex_unlock(&bfqd->queue->blkcg_mutex);
         |                       ~~~~~~~~~~~  ^
   2 errors generated.


vim +2648 block/bfq-iosched.c

  2642	
  2643	static void bfq_end_wr(struct bfq_data *bfqd)
  2644	{
  2645		struct bfq_queue *bfqq;
  2646		int i;
  2647	
> 2648		mutex_lock(&bfqd->queue->blkcg_mutex);
  2649		spin_lock_irq(&bfqd->lock);
  2650	
  2651		for (i = 0; i < bfqd->num_actuators; i++) {
  2652			list_for_each_entry(bfqq, &bfqd->active_list[i], bfqq_list)
  2653				bfq_bfqq_end_wr(bfqq);
  2654		}
  2655		list_for_each_entry(bfqq, &bfqd->idle_list, bfqq_list)
  2656			bfq_bfqq_end_wr(bfqq);
  2657		bfq_end_wr_async(bfqd);
  2658	
  2659		spin_unlock_irq(&bfqd->lock);
  2660		mutex_unlock(&bfqd->queue->blkcg_mutex);
  2661	}
  2662	

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki
Re: [PATCH v2 2/7] bfq: protect q->blkg_list iteration in bfq_end_wr_async() with blkcg_mutex
Posted by kernel test robot 6 days, 7 hours ago 
Hi Yu,

kernel test robot noticed the following build errors:

[auto build test ERROR on axboe/for-next]
[also build test ERROR on linus/master v6.19-rc8 next-20260202]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Yu-Kuai/blk-cgroup-protect-q-blkg_list-iteration-in-blkg_destroy_all-with-blkcg_mutex/20260203-161356
base:   https://git.kernel.org/pub/scm/linux/kernel/git/axboe/linux.git for-next
patch link:    https://lore.kernel.org/r/20260203080602.726505-3-yukuai%40fnnas.com
patch subject: [PATCH v2 2/7] bfq: protect q->blkg_list iteration in bfq_end_wr_async() with blkcg_mutex
config: i386-buildonly-randconfig-002-20260203 (https://download.01.org/0day-ci/archive/20260203/202602032018.BRG7c7LT-lkp@intel.com/config)
compiler: gcc-13 (Debian 13.3.0-16) 13.3.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260203/202602032018.BRG7c7LT-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202602032018.BRG7c7LT-lkp@intel.com/

All errors (new ones prefixed by >>):

   In file included from include/linux/seqlock.h:19,
                    from include/linux/mmzone.h:17,
                    from include/linux/gfp.h:7,
                    from include/linux/umh.h:4,
                    from include/linux/kmod.h:9,
                    from include/linux/module.h:18,
                    from block/bfq-iosched.c:116:
   block/bfq-iosched.c: In function 'bfq_end_wr':
>> block/bfq-iosched.c:2648:32: error: 'struct request_queue' has no member named 'blkcg_mutex'
    2648 |         mutex_lock(&bfqd->queue->blkcg_mutex);
         |                                ^~
   include/linux/mutex.h:193:44: note: in definition of macro 'mutex_lock'
     193 | #define mutex_lock(lock) mutex_lock_nested(lock, 0)
         |                                            ^~~~
   block/bfq-iosched.c:2660:34: error: 'struct request_queue' has no member named 'blkcg_mutex'
    2660 |         mutex_unlock(&bfqd->queue->blkcg_mutex);
         |                                  ^~


vim +2648 block/bfq-iosched.c

  2642	
  2643	static void bfq_end_wr(struct bfq_data *bfqd)
  2644	{
  2645		struct bfq_queue *bfqq;
  2646		int i;
  2647	
> 2648		mutex_lock(&bfqd->queue->blkcg_mutex);
  2649		spin_lock_irq(&bfqd->lock);
  2650	
  2651		for (i = 0; i < bfqd->num_actuators; i++) {
  2652			list_for_each_entry(bfqq, &bfqd->active_list[i], bfqq_list)
  2653				bfq_bfqq_end_wr(bfqq);
  2654		}
  2655		list_for_each_entry(bfqq, &bfqd->idle_list, bfqq_list)
  2656			bfq_bfqq_end_wr(bfqq);
  2657		bfq_end_wr_async(bfqd);
  2658	
  2659		spin_unlock_irq(&bfqd->lock);
  2660		mutex_unlock(&bfqd->queue->blkcg_mutex);
  2661	}
  2662	

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki
Re: [PATCH v2 2/7] bfq: protect q->blkg_list iteration in bfq_end_wr_async() with blkcg_mutex
Posted by Yu Kuai 6 days, 7 hours ago 
Hi,

在 2026/2/3 20:54, kernel test robot 写道:
> Hi Yu,
>
> kernel test robot noticed the following build errors:
>
> [auto build test ERROR on axboe/for-next]
> [also build test ERROR on linus/master v6.19-rc8 next-20260202]
> [If your patch is applied to the wrong git tree, kindly drop us a note.
> And when submitting patch, we suggest to use '--base' as documented in
> https://git-scm.com/docs/git-format-patch#_base_tree_information]
>
> url:    https://github.com/intel-lab-lkp/linux/commits/Yu-Kuai/blk-cgroup-protect-q-blkg_list-iteration-in-blkg_destroy_all-with-blkcg_mutex/20260203-161356
> base:   https://git.kernel.org/pub/scm/linux/kernel/git/axboe/linux.git for-next
> patch link:    https://lore.kernel.org/r/20260203080602.726505-3-yukuai%40fnnas.com
> patch subject: [PATCH v2 2/7] bfq: protect q->blkg_list iteration in bfq_end_wr_async() with blkcg_mutex
> config: i386-buildonly-randconfig-002-20260203 (https://download.01.org/0day-ci/archive/20260203/202602032018.BRG7c7LT-lkp@intel.com/config)
> compiler: gcc-13 (Debian 13.3.0-16) 13.3.0
> reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260203/202602032018.BRG7c7LT-lkp@intel.com/reproduce)
>
> If you fix the issue in a separate patch/commit (i.e. not just a new version of
> the same patch/commit), kindly add following tags
> | Reported-by: kernel test robot <lkp@intel.com>
> | Closes: https://lore.kernel.org/oe-kbuild-all/202602032018.BRG7c7LT-lkp@intel.com/

Looks like this is due to CONFIG_BLK_CGROUP is disabled, will fix this in the next
version.

>
> All errors (new ones prefixed by >>):
>
>     In file included from include/linux/seqlock.h:19,
>                      from include/linux/mmzone.h:17,
>                      from include/linux/gfp.h:7,
>                      from include/linux/umh.h:4,
>                      from include/linux/kmod.h:9,
>                      from include/linux/module.h:18,
>                      from block/bfq-iosched.c:116:
>     block/bfq-iosched.c: In function 'bfq_end_wr':
>>> block/bfq-iosched.c:2648:32: error: 'struct request_queue' has no member named 'blkcg_mutex'
>      2648 |         mutex_lock(&bfqd->queue->blkcg_mutex);
>           |                                ^~
>     include/linux/mutex.h:193:44: note: in definition of macro 'mutex_lock'
>       193 | #define mutex_lock(lock) mutex_lock_nested(lock, 0)
>           |                                            ^~~~
>     block/bfq-iosched.c:2660:34: error: 'struct request_queue' has no member named 'blkcg_mutex'
>      2660 |         mutex_unlock(&bfqd->queue->blkcg_mutex);
>           |                                  ^~
>
>
> vim +2648 block/bfq-iosched.c
>
>    2642	
>    2643	static void bfq_end_wr(struct bfq_data *bfqd)
>    2644	{
>    2645		struct bfq_queue *bfqq;
>    2646		int i;
>    2647	
>> 2648		mutex_lock(&bfqd->queue->blkcg_mutex);
>    2649		spin_lock_irq(&bfqd->lock);
>    2650	
>    2651		for (i = 0; i < bfqd->num_actuators; i++) {
>    2652			list_for_each_entry(bfqq, &bfqd->active_list[i], bfqq_list)
>    2653				bfq_bfqq_end_wr(bfqq);
>    2654		}
>    2655		list_for_each_entry(bfqq, &bfqd->idle_list, bfqq_list)
>    2656			bfq_bfqq_end_wr(bfqq);
>    2657		bfq_end_wr_async(bfqd);
>    2658	
>    2659		spin_unlock_irq(&bfqd->lock);
>    2660		mutex_unlock(&bfqd->queue->blkcg_mutex);
>    2661	}
>    2662	
>
-- 
Thansk,
Kuai

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