From: Tang Junhui <tang.junhui@xxxxxxxxxx>
>On 24/01/2018 2:54 PM, tang.junhui@xxxxxxxxxx wrote:
>> From: Tang Junhui <tang.junhui@xxxxxxxxxx>
>>
>> In btree_flush_write(), two places need to take a locker to
>> avoid races:
>>
>> Firstly, we need take rcu read locker to protect the bucket_hash
>> traverse, since hlist_for_each_entry_rcu() must be called under
>> the protection of rcu read locker.
>>
>> Secondly, we need take b->write_lock locker to protect journal
>> of the btree node, otherwise, the btree node may have been
>> written, and the journal have been assign to NULL.
>>
>> Signed-off-by: Tang Junhui <tang.junhui@xxxxxxxxxx>
>> ---
>> drivers/md/bcache/journal.c | 7 ++++++-
>> 1 file changed, 6 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/md/bcache/journal.c b/drivers/md/bcache/journal.c
>> index 02a98dd..505f9f3 100644
>> --- a/drivers/md/bcache/journal.c
>> +++ b/drivers/md/bcache/journal.c
>> @@ -375,7 +375,9 @@ static void btree_flush_write(struct cache_set *c)
>> retry:
>> best = NULL;
>>
>> - for_each_cached_btree(b, c, i)
>> + rcu_read_lock();
>> + for_each_cached_btree(b, c, i) {
>> + mutex_lock(&b->write_lock);
>> if (btree_current_write(b)->journal) {
>> if (!best)
>> best = b;
>> @@ -385,6 +387,9 @@ static void btree_flush_write(struct cache_set *c)
>> best = b;
>> }
>> }
>> + mutex_unlock(&b->write_lock);
>> + }
>> + rcu_read_unlock();
>>
>> b = best;
>> if (b) {
>>
>
>Hi Junhui,
>
>Do you run into some real problem ? The patch looks good to me at first
>glance, but I need time to dig it more before I provide my response.
>
>Thanks.
No real problem run out, I find it by code reading, I think we'd better
lock it for safety.
Thanks,
Tang Junhui
