| Message ID | 20170921195458.53890-1-colyli@suse.de (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
Hey Coly-- On Thu, Sep 21, 2017 at 12:54 PM, Coly Li <colyli@suse.de> wrote: > When bcache does read I/Os, for example in writeback or writethrough mode, > if a read request on cache device is failed, bcache will try to recovery > the request by reading from cached device. If the data on cached device is > not synced with cache device, then requester will get a stale data. [...] > + if (s->recoverable && > + (dc && !atomic_read(&dc->has_dirty)) { Looks like this is missing a parens. Thx, Mike
On 2017/10/17 上午1:39, Michael Lyle wrote: > Hey Coly-- > > On Thu, Sep 21, 2017 at 12:54 PM, Coly Li <colyli@suse.de> wrote: >> When bcache does read I/Os, for example in writeback or writethrough mode, >> if a read request on cache device is failed, bcache will try to recovery >> the request by reading from cached device. If the data on cached device is >> not synced with cache device, then requester will get a stale data. > [...] >> + if (s->recoverable && >> + (dc && !atomic_read(&dc->has_dirty)) { > > Looks like this is missing a parens. Hi Mike, Oops, I am blind ... Thanks for figure out this. V4 patch is out, and I think you may change Acked-by to Reviewed-by, because you reviewed the code and pointed out problem :-) Thanks.
diff --git a/drivers/md/bcache/request.c b/drivers/md/bcache/request.c index 681b4f12b05a..e7f769ff7234 100644 --- a/drivers/md/bcache/request.c +++ b/drivers/md/bcache/request.c @@ -697,8 +697,16 @@ static void cached_dev_read_error(struct closure *cl) { struct search *s = container_of(cl, struct search, cl); struct bio *bio = &s->bio.bio; + struct cached_dev *dc = container_of(s->d, struct cached_dev, disk); - if (s->recoverable) { + /* + * If cache device is dirty (dc->has_dirty is non-zero), then + * recovery a failed read request from cached device may get a + * stale data back. So read failure recovery is only permitted + * when cache device is clean. + */ + if (s->recoverable && + (dc && !atomic_read(&dc->has_dirty)) { /* Retry from the backing device: */ trace_bcache_read_retry(s->orig_bio);
When bcache does read I/Os, for example in writeback or writethrough mode, if a read request on cache device is failed, bcache will try to recovery the request by reading from cached device. If the data on cached device is not synced with cache device, then requester will get a stale data. For critical storage system like database, providing stale data from recovery may result an application level data corruption, which is unacceptible. With this patch, for a failed read request in writeback or writethrough mode, recovery a recoverable read request only happens when cache device is clean. That is to say, all data on cached device is up to update. For other cache modes in bcache, read request will never hit cached_dev_read_error(), they don't need this patch. Please note, because cache mode can be switched arbitrarily in run time, a writethrough mode might be switched from a writeback mode. Therefore checking dc->has_data in writethrough mode still makes sense. Changelog: v3: By response from Kent Oversteet, he thinks recovering stale data is a bug to fix, and option to permit it is unneccessary. So this version the sysfs file is removed. v2: rename sysfs entry from allow_stale_data_on_failure to allow_stale_data_on_failure, and fix the confusing commit log. v1: initial patch posted. Signed-off-by: Coly Li <colyli@suse.de> Reported-by: Arne Wolf <awolf@lenovo.com> Cc: Kent Overstreet <kent.overstreet@gmail.com> Cc: Michael Lyle <mlyle@lyle.org> Cc: Nix <nix@esperi.org.uk> Cc: Kai Krakow <hurikhan77@gmail.com> Cc: Eric Wheeler <bcache@lists.ewheeler.net> Cc: Junhui Tang <tang.junhui@zte.com.cn> Cc: stable@vger.kernel.org --- drivers/md/bcache/request.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-)