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[libzstd] Fix ZSTD_compress2() for multithreaded compression

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`ZSTD_compress2()` wouldn't wait for multithreaded compression to
finish. We didn't find this because ZSTDMT will block when it can
compress all in one go, but it can't do that if it doesn't have enough
output space, or if `ZSTD_c_rsyncable` is enabled.

Since we will already sometimes block when using `ZSTD_e_end`, I've
changed `ZSTD_e_end` and `ZSTD_e_flush` to guarantee maximum forward
progress. This simplifies the API, and helps users avoid the easy bug
that was made in `ZSTD_compress2()`

* Found by the libfuzzer fuzzers.
* Added a test case that catches the problem.
* I will make the fuzzers sometimes allocate less than
  `ZSTD_compressBound()` output space.
This commit is contained in:
Nick Terrell
2019-04-09 16:24:17 -07:00
parent 7a1fde2957
commit 48a6427d22
3 changed files with 40 additions and 6 deletions
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lib/compress/zstd_compress.c
+14 -4
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@@ -4179,18 +4179,28 @@ size_t ZSTD_compressStream2( ZSTD_CCtx* cctx,
/* compression stage */
#ifdef ZSTD_MULTITHREAD
if (cctx->appliedParams.nbWorkers > 0) {
int const forceMaxProgress = (endOp == ZSTD_e_flush || endOp == ZSTD_e_end);
size_t flushMin;
assert(forceMaxProgress || endOp == ZSTD_e_continue /* Protection for a new flush type */);
if (cctx->cParamsChanged) {
ZSTDMT_updateCParams_whileCompressing(cctx->mtctx, &cctx->requestedParams);
cctx->cParamsChanged = 0;
}
{ size_t const flushMin = ZSTDMT_compressStream_generic(cctx->mtctx, output, input, endOp);
do {
flushMin = ZSTDMT_compressStream_generic(cctx->mtctx, output, input, endOp);
if ( ZSTD_isError(flushMin)
|| (endOp == ZSTD_e_end && flushMin == 0) ) { /* compression completed */
ZSTD_CCtx_reset(cctx, ZSTD_reset_session_only);
}
DEBUGLOG(5, "completed ZSTD_compressStream2 delegating to ZSTDMT_compressStream_generic");
return flushMin;
} }
FORWARD_IF_ERROR(flushMin);
} while (forceMaxProgress && flushMin != 0 && output->pos < output->size);
DEBUGLOG(5, "completed ZSTD_compressStream2 delegating to ZSTDMT_compressStream_generic");
/* Either we don't require maximum forward progress, we've finished the
* flush, or we are out of output space.
*/
assert(!forceMaxProgress || flushMin == 0 || output->pos == output->size);
return flushMin;
}
#endif
FORWARD_IF_ERROR( ZSTD_compressStream_generic(cctx, output, input, endOp) );
DEBUGLOG(5, "completed ZSTD_compressStream2");