mirror of
https://github.com/facebook/rocksdb.git
synced 2026-07-07 14:47:40 +08:00
Anand Ananthabhotla
a0ad7887c9
Summary: Pull Request resolved: https://github.com/facebook/rocksdb/pull/14907 `RandomAccessFileReader::ReadAsync` took its "already aligned" fast path when the request offset and length were sector-aligned, forwarding the caller's `req` (including its `scratch` pointer) straight to the FileSystem. A null `scratch` trivially satisfied the alignment check (`uintptr_t(nullptr) & (alignment - 1) == 0`), so when a caller submitted an aligned request with `scratch == nullptr` and an `aligned_buf` out-parameter for the reader to allocate into, the null buffer was submitted to the async read. For direct IO with io_uring this becomes a null `iovec` base, which the kernel rejects with `EFAULT` (surfaced as `Req failed: Unknown error -14`). This is exactly how `IODispatcher` submits MultiScan async reads for plain direct IO (`scratch == nullptr`, `aligned_buf` provided), so the failure manifested intermittently as `db_stress` iterator divergence ("Iterator diverged from control iterator") in crash tests with `use_direct_reads=1 --use_multiscan=1 --multiscan_use_async_io=1`. It is intermittent because it only triggers when the coalesced read's offset and length both happen to be sector-aligned. Task T267030385. The fix excludes the aligned fast path when the caller provided no `scratch` but did provide an `aligned_buf`, forcing the allocating path so a valid backing buffer is always handed to the async read. This matches the existing behavior of the synchronous `Read`, which already guards its aligned fast path with `scratch != nullptr`. Reviewed By: xingbowang Differential Revision: D110361301 fbshipit-source-id: 3884f7ddbc746cf51b2566d74918e2fb97233dcb