> 2025年1月14日 11:21，Kun Hu <huk23@xxxxxxxxxxxxxx> 写道：
>
>> If vfs_flush() is called with queue frozen, the queue freeze lock may be
>> connected with FS internal lock, and potential deadlock could be
>> triggered.
>>
>> Fix it by moving vfs_flush() out of queue freezing.
>>
>> Reported-by: Kun Hu <huk23@xxxxxxxxxxxxxx>
>> Reported-by: Jiaji Qin <jjtan24@xxxxxxxxxxxxxx>
>> Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx>
>> ---
>> drivers/block/loop.c | 21 +++++++++++++++------
>> 1 file changed, 15 insertions(+), 6 deletions(-)
>>
>> diff --git a/drivers/block/loop.c b/drivers/block/loop.c
>> index 1ec7417c7f00..9adf496b3f93 100644
>> --- a/drivers/block/loop.c
>> +++ b/drivers/block/loop.c
>> @@ -203,7 +203,7 @@ static bool lo_can_use_dio(struct loop_device *lo)
>> * loop_get_status will always report the effective LO_FLAGS_DIRECT_IO flag and
>> * not the originally passed in one.
>> */
>> -static inline void loop_update_dio(struct loop_device *lo)
>> +static inline bool loop_update_dio(struct loop_device *lo)
>> {
>> bool dio_in_use = lo->lo_flags & LO_FLAGS_DIRECT_IO;
>>
>> @@ -217,8 +217,7 @@ static inline void loop_update_dio(struct loop_device *lo)
>> lo->lo_flags &= ~LO_FLAGS_DIRECT_IO;
>>
>> /* flush dirty pages before starting to issue direct I/O */
>> - if ((lo->lo_flags & LO_FLAGS_DIRECT_IO) && !dio_in_use)
>> - vfs_fsync(lo->lo_backing_file, 0);
>> + return (lo->lo_flags & LO_FLAGS_DIRECT_IO) && !dio_in_use;
>> }
>>
>> /**
>> @@ -589,6 +588,7 @@ static int loop_change_fd(struct loop_device *lo, struct block_device *bdev,
>> int error;
>> bool partscan;
>> bool is_loop;
>> + bool flush;
>>
>> if (!file)
>> return -EBADF;
>> @@ -629,11 +629,14 @@ static int loop_change_fd(struct loop_device *lo, struct block_device *bdev,
>> lo->old_gfp_mask = mapping_gfp_mask(file->f_mapping);
>> mapping_set_gfp_mask(file->f_mapping,
>> lo->old_gfp_mask & ~(__GFP_IO|__GFP_FS));
>> - loop_update_dio(lo);
>> + flush = loop_update_dio(lo);
>> blk_mq_unfreeze_queue(lo->lo_queue);
>> partscan = lo->lo_flags & LO_FLAGS_PARTSCAN;
>> loop_global_unlock(lo, is_loop);
>>
>> + if (flush)
>> + vfs_fsync(lo->lo_backing_file, 0);
>> +
>> /*
>> * Flush loop_validate_file() before fput(), for l->lo_backing_file
>> * might be pointing at old_file which might be the last reference.
>> @@ -1255,6 +1258,7 @@ loop_set_status(struct loop_device *lo, const struct loop_info64 *info)
>> int err;
>> bool partscan = false;
>> bool size_changed = false;
>> + bool flush = false;
>>
>> err = mutex_lock_killable(&lo->lo_mutex);
>> if (err)
>> @@ -1292,7 +1296,7 @@ loop_set_status(struct loop_device *lo, const struct loop_info64 *info)
>> }
>>
>> /* update the direct I/O flag if lo_offset changed */
>> - loop_update_dio(lo);
>> + flush = loop_update_dio(lo);
>>
>> out_unfreeze:
>> blk_mq_unfreeze_queue(lo->lo_queue);
>> @@ -1302,6 +1306,8 @@ loop_set_status(struct loop_device *lo, const struct loop_info64 *info)
>> mutex_unlock(&lo->lo_mutex);
>> if (partscan)
>> loop_reread_partitions(lo);
>> + if (flush)
>> + vfs_fsync(lo->lo_backing_file, 0);
>>
>> return err;
>> }
>> @@ -1473,6 +1479,7 @@ static int loop_set_block_size(struct loop_device *lo, unsigned long arg)
>> {
>> struct queue_limits lim;
>> int err = 0;
>> + bool flush;
>>
>> if (lo->lo_state != Lo_bound)
>> return -ENXIO;
>> @@ -1488,8 +1495,10 @@ static int loop_set_block_size(struct loop_device *lo, unsigned long arg)
>>
>> blk_mq_freeze_queue(lo->lo_queue);
>> err = queue_limits_commit_update(lo->lo_queue, &lim);
>> - loop_update_dio(lo);
>> + flush = loop_update_dio(lo);
>> blk_mq_unfreeze_queue(lo->lo_queue);
>> + if (flush)
>> + vfs_fsync(lo->lo_backing_file, 0);
>>
>> return err;
>> }
>> --
>> 2.44.0
>>
Hi Ming,
I wanted to follow up as I haven’t yet seen the fix you provided, titled “[PATCH] loop: don't call vfs_flush() with queue frozen” and “[PATCH] loop: move vfs_fsync() out of loop_update_dio()" in the kernel tree. Could you kindly confirm if this resolves the issue we’ve been discussing? Additionally, I would greatly appreciate it if you could share any updates regarding the resolution of this matter.
