On 12/01/2018 11:24 PM, Pavel Vazharov wrote:
> There was a possibility for infinite do-while loop inside the GC thread
> function in case of total failure of the caching device. I was able to
> reproduce it 3 times simulating disappearing of the caching device via
> 'echo 1 > /sys/block/<dev>/device/delete'. In that case the btree_root
> starts to return non zero and non -EAGAIN result, 'gc failed' message
> start to fill the kernel log and the do-while becomes infinite loop
> occupying single CPU core at 100%.
> There is already a logic which unregisters the cache_set (or panics) in
> case of io errors and thus we exit the loop here if the unregistering
> procedure has already started.
>
> Signed-off-by: Pavel Vazharov <freakpv@xxxxxxxxx>
> ---
> drivers/md/bcache/btree.c | 8 ++++++--
> 1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/md/bcache/btree.c b/drivers/md/bcache/btree.c
> index 81e8dc3..a672081 100644
> --- a/drivers/md/bcache/btree.c
> +++ b/drivers/md/bcache/btree.c
> @@ -1748,8 +1748,12 @@ static void bch_btree_gc(struct cache_set *c)
> closure_sync(&writes);
> cond_resched();
>
> - if (ret && ret != -EAGAIN)
> - pr_warn("gc failed!");
> + if (ret && ret != -EAGAIN) {
> + if (test_bit(CACHE_SET_UNREGISTERING, &c->flags))
> + break;
> + else
> + pr_warn("gc failed!");
> + }
> } while (ret);
>
> bch_btree_gc_finish(c);
>
Hi Pavel,
I see the point here. But there are 2 code paths to call
cache_set_flush(), one is from bch_cache_set_error(), one is from sysfs
interface (echo 1 > /sys/fs/bcache/<UUID>/stop).
CACHE_SET_UNREGISTERING is set in the first code path, the another code
path from sysfs does not set CACHE_SET_UNREGISTERING. In this case maybe
the above while-loop can not be stopped.
In my device failure cache set, I add an io_disable (in v2 it is
CACHE_SET_IO_DISABLE flag) to disable all cache set I/O, maybe it can be
used to check the condition and break the while-loop.
Thanks for the hint, I will also try to fix it in my patch set. If you
don't mind, I am glad to have your "Reviewed-by:" after I post the v2
patch set.
Thanks.
--
Coly Li
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