On 10/29/19 7:01 PM, Joe Thornber wrote:
> On Tue, Oct 29, 2019 at 05:07:30AM +0000, Heming Zhao wrote:
>> Hello Joe,
>>
>> Please check my comments for your commit 2938b4dcc & 6b0d969b
>>
>> 1. b->ref_count is non-zero, and write error happens, the data never release?
>> (no place to call _unlink_block & _free_block)
>
> Correct, the data will not be released until the client calls bcache_abort_fd(), to
> indicate that it's giving up on the write. That way the client is free to retry
> io, eg, see this unit test:
>
> 689│static void test_write_bad_issue_stops_flush(void *context)
> 1│{
> 2│ struct fixture *f = context;
> 3│ struct mock_engine *me = f->me;
> 4│ struct bcache *cache = f->cache;
> 5│ struct block *b;
> 6│ int fd = 17;
> 7│
> 8│ T_ASSERT(bcache_get(cache, fd, 0, GF_ZERO, &b));
> 9│ _expect_write_bad_issue(me, fd, 0);
> 10│ bcache_put(b);
> 11│ T_ASSERT(!bcache_flush(cache));
> 12│
> 13│ // we'll let it succeed the second time
> 14│ _expect_write(me, fd, 0);
> 15│ _expect(me, E_WAIT);
> 16│ T_ASSERT(bcache_flush(cache));
> 17│}
>
you are right.
>
>> 2. when dev_write_bytes failed, call dev_unset_last_byte with "fd=-1" is wrong.
>
> Quite possibly, this unset_last_byte stuff is a hack that Dave put in. I'll look some more.
>
>
>> 3. I still think below error handling should be added.
>> Below base on stable-2.02, but the core idea is same, should access the return value of io_submit & io_getevents.
>>
>> ```
>> static bool _async_issue(struct io_engine *ioe, enum dir d, int fd,
>> ... ...
>> if (r < 0) {
>> _cb_free(e->cbs, cb);
>> + ((struct block *)context)->error = r; <== assign errno & print warning
>> + log_warn("io_submit <%c> off %llu bytes %llu return %d:%s",
>> + (d == DIR_READ) ? 'R' : 'W', (long long unsigned)offset,
>> + (long long unsigned)nbytes, r, strerror(-r));
>> return false;
>> }
>>
>> static void _issue_low_level(struct block *b, enum dir d)
>> ... ...
>> dm_list_move(&cache->io_pending, &b->list);
>>
>> if (!cache->engine->issue(cache->engine, d, b->fd, sb, se, b->data, b)) {
>> - /* FIXME: if io_submit() set an errno, return that instead of EIO? */
>> - _complete_io(b, -EIO);
>> + _complete_io(b, b->error); <=== this pass the right errno to caller.
>> return;
>> }
>> }
>
> Yep, this is good. Added.
>
>
>> -static void _wait_all(struct bcache *cache)
>> +static bool _wait_all(struct bcache *cache) <=== change to return error
>> {
>> + bool ret = true;
>> while (!dm_list_empty(&cache->io_pending))
>> - _wait_io(cache);
>> + ret = _wait_io(cache);
>> + return ret;
>> }
>>
>> -static void _wait_specific(struct block *b)
>> +static bool _wait_specific(struct block *b) <=== change to return error
>> {
>> + bool ret = true;
>> while (_test_flags(b, BF_IO_PENDING))
>> - _wait_io(b->cache);
>> + ret = _wait_io(b->cache);
>> + return ret;
>> }
>
> No, the wait functions just wait for io to complete, they're not interested
> in whether it succeeded. That's what b->error is for.
>
if io_getevents failed, how do you do? just ignore?
the data still in cache->io_pending not in cache->errored.
>
>>
>> bool bcache_flush(struct bcache *cache) <==== add more error handling
>> {
>> + bool write_ret = true, wait_ret = true;
>>
>> ... ...
>> _issue_write(b);
>> + if (b->error) write_ret = false;
>> }
>>
>> - _wait_all(cache);
>> + wait_ret = _wait_all(cache);
>>
>> - return dm_list_empty(&cache->errored);
>> + if (write_ret == false || wait_ret == false ||
>> + !dm_list_empty(&cache->errored))
>> + return false;
>> + else
>> + return true;
>> }
>
> I don't understand how this changes the behaviour from just checking the
> size of cache->errored.
this is stable-2.02 code. master branch like below.
the core idea is to check the io_submit & io_getevents return value. (refer above codes changes)
```
bool bcache_flush(struct bcache *cache)
{
+ bool write_ret = true, wait_ret = true;
+
// Only dirty data is on the errored list, since bad read blocks get
// recycled straight away. So we put these back on the dirty list, and
// try and rewrite everything.
dm_list_splice(&cache->dirty, &cache->errored);
while (!dm_list_empty(&cache->dirty)) {
struct block *b = dm_list_item(_list_pop(&cache->dirty), struct block);
if (b->ref_count || _test_flags(b, BF_IO_PENDING)) {
// The superblock may well be still locked.
continue;
}
- _issue_write(b);
+ if (b->error) write_ret = false;
}
- _wait_all(cache);
+ wait_ret = _wait_all(cache);
- return dm_list_empty(&cache->errored);
+ if (write_ret == false || wait_ret == false ||
+ !dm_list_empty(&cache->errored))
+ return false;
+ else
+ return true;
}
```
>
> - Joe
>
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