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│}
> 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.
>
> 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.
- Joe
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