os/bluestore: fix bugs in bluefs and bdev flush #13911
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Signed-off-by: Sage Weil <sage@redhat.com>
flush() may be called from multiple racing threads (notably, rocksdb can call fsync via bluefs at any time), and we need to make sure that if one thread sees the io_since_flush command and does an actual flush, that other racing threads also wait until that flush is complete. This is accomplished with a simple mutex! Also, set the flag on IO *completion*, since flush is only a promise about completed IOs, not submitted IOs. Document. Fixes: http://tracker.ceph.com/issues/19251 Signed-off-by: Sage Weil <sage@redhat.com>
We need to flush any new writes on any fsync(). Notably, this includes the rocksdb log. However, previously _fsync was only doing a bdev flush if we also had a dirty bluefs journal and called into _sync_and_flush_journal. If we didn't, we weren't doing a flush() at all, which could lead to corrupted data. Fix this by moving the first flush_bdev *out* of _sync_and_flush_log. (The second one is there to flush the bluefs journal; the first one was to ensure prior writes are stable.) Instead, flush prior writes in all of the callers prior to calling _sync_and_flush_log. This includes _fsync (and fixes the bug by covering the non-journal-flush path) as well as several other callers. Fixes: http://tracker.ceph.com/issues/19250 Signed-off-by: Sage Weil <sage@redhat.com>
yuyuyu101
reviewed
Mar 10, 2017
| // aio completion notification will not return before that aio is | ||
| // stable on disk: whichever thread sees the flag first will block | ||
| // followers until the aio is stable. | ||
| std::lock_guard<std::mutex> l(flush_mutex); |
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I suggest we add a perf counter to this flush_mutex lock contention. I suspect it will cause serious performance spike...
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in practice it is very rare that multiple threads call flush... i only saw
it after quite a bit of testing, and it only happened because rocksdb
(compaction?). and if two threads *do* collide on this lock, the whole
point is that they *must* block in order to ensure their data is stable on
disk.
unless i'm misunderstanding what you mean by 'lock contention' in this
case?
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OH, I got the actual idea. |
yuyuyu101
approved these changes
Mar 10, 2017
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http://tracker.ceph.com/issues/19251
http://tracker.ceph.com/issues/19250
These will get backported to kraken too.