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Lunev" To: qemu-block@nongnu.org, qemu-devel@nongnu.org Cc: den@openvz.org, Kevin Wolf , Hanna Reitz , Vladimir Sementsov-Ogievskiy Subject: [PATCH 2/3] block/qapi: take stats->lock when reading BlockAcctStats for query-blockstats Date: Thu, 23 Jul 2026 14:37:44 +0200 Message-ID: <20260723123745.3294227-3-den@openvz.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260723123745.3294227-1-den@openvz.org> References: <20260723123745.3294227-1-den@openvz.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=2a00:1450:4864:20::632; envelope-from=den@openvz.org; helo=mail-ej1-x632.google.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: qemu development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org bdrv_query_blk_stats() reads nr_bytes[], nr_ops[], failed_ops[], invalid_ops[], merged[], total_time_ns[], last_access_time_ns, and the latency histogram bins directly off BlockAcctStats, without taking stats->lock. block_account_one_io() updates the same fields under that lock from whatever iothread completes the I/O, so this is an unsynchronized read of concurrently-updated state. This is a narrower issue than the one fixed for the histogram setters. query-blockstats and block-latency-histogram-set are both plain (non-allow-oob) QMP commands, so they always run serialized on the monitor thread and can never execute concurrently with each other. Take stats->lock around the read for consistency. Signed-off-by: Denis V. Lunev CC: Kevin Wolf CC: Hanna Reitz CC: Vladimir Sementsov-Ogievskiy --- block/qapi.c | 102 ++++++++++++++++++++++++++++++--------------------- 1 file changed, 60 insertions(+), 42 deletions(-) diff --git a/block/qapi.c b/block/qapi.c index eabfbfc258..c3f20832b7 100644 --- a/block/qapi.c +++ b/block/qapi.c @@ -535,49 +535,67 @@ static void bdrv_query_blk_stats(BlockDeviceStats *ds, BlockBackend *blk) BlockAcctTimedStats *ts = NULL; BlockLatencyHistogram *hgram; - ds->rd_bytes = stats->nr_bytes[BLOCK_ACCT_READ]; - ds->wr_bytes = stats->nr_bytes[BLOCK_ACCT_WRITE]; - ds->zone_append_bytes = stats->nr_bytes[BLOCK_ACCT_ZONE_APPEND]; - ds->unmap_bytes = stats->nr_bytes[BLOCK_ACCT_UNMAP]; - ds->rd_operations = stats->nr_ops[BLOCK_ACCT_READ]; - ds->wr_operations = stats->nr_ops[BLOCK_ACCT_WRITE]; - ds->zone_append_operations = stats->nr_ops[BLOCK_ACCT_ZONE_APPEND]; - ds->unmap_operations = stats->nr_ops[BLOCK_ACCT_UNMAP]; - - ds->failed_rd_operations = stats->failed_ops[BLOCK_ACCT_READ]; - ds->failed_wr_operations = stats->failed_ops[BLOCK_ACCT_WRITE]; - ds->failed_zone_append_operations = - stats->failed_ops[BLOCK_ACCT_ZONE_APPEND]; - ds->failed_flush_operations = stats->failed_ops[BLOCK_ACCT_FLUSH]; - ds->failed_unmap_operations = stats->failed_ops[BLOCK_ACCT_UNMAP]; - - ds->invalid_rd_operations = stats->invalid_ops[BLOCK_ACCT_READ]; - ds->invalid_wr_operations = stats->invalid_ops[BLOCK_ACCT_WRITE]; - ds->invalid_zone_append_operations = - stats->invalid_ops[BLOCK_ACCT_ZONE_APPEND]; - ds->invalid_flush_operations = - stats->invalid_ops[BLOCK_ACCT_FLUSH]; - ds->invalid_unmap_operations = stats->invalid_ops[BLOCK_ACCT_UNMAP]; - - ds->rd_merged = stats->merged[BLOCK_ACCT_READ]; - ds->wr_merged = stats->merged[BLOCK_ACCT_WRITE]; - ds->zone_append_merged = stats->merged[BLOCK_ACCT_ZONE_APPEND]; - ds->unmap_merged = stats->merged[BLOCK_ACCT_UNMAP]; - ds->flush_operations = stats->nr_ops[BLOCK_ACCT_FLUSH]; - ds->wr_total_time_ns = stats->total_time_ns[BLOCK_ACCT_WRITE]; - ds->zone_append_total_time_ns = - stats->total_time_ns[BLOCK_ACCT_ZONE_APPEND]; - ds->rd_total_time_ns = stats->total_time_ns[BLOCK_ACCT_READ]; - ds->flush_total_time_ns = stats->total_time_ns[BLOCK_ACCT_FLUSH]; - ds->unmap_total_time_ns = stats->total_time_ns[BLOCK_ACCT_UNMAP]; - - ds->has_idle_time_ns = stats->last_access_time_ns > 0; - if (ds->has_idle_time_ns) { - ds->idle_time_ns = block_acct_idle_time_ns(stats); - } + /* + * nr_bytes[] etc. are mutated under stats->lock by block_account_one_io() + * from an iothread, and latency_histogram[].{nbins,boundaries,bins} can + * be freed and reallocated by a concurrent block_latency_histogram_set() + * on the monitor thread, so every read here needs the same lock. + */ + WITH_QEMU_LOCK_GUARD(&stats->lock) { + ds->rd_bytes = stats->nr_bytes[BLOCK_ACCT_READ]; + ds->wr_bytes = stats->nr_bytes[BLOCK_ACCT_WRITE]; + ds->zone_append_bytes = stats->nr_bytes[BLOCK_ACCT_ZONE_APPEND]; + ds->unmap_bytes = stats->nr_bytes[BLOCK_ACCT_UNMAP]; + ds->rd_operations = stats->nr_ops[BLOCK_ACCT_READ]; + ds->wr_operations = stats->nr_ops[BLOCK_ACCT_WRITE]; + ds->zone_append_operations = stats->nr_ops[BLOCK_ACCT_ZONE_APPEND]; + ds->unmap_operations = stats->nr_ops[BLOCK_ACCT_UNMAP]; + + ds->failed_rd_operations = stats->failed_ops[BLOCK_ACCT_READ]; + ds->failed_wr_operations = stats->failed_ops[BLOCK_ACCT_WRITE]; + ds->failed_zone_append_operations = + stats->failed_ops[BLOCK_ACCT_ZONE_APPEND]; + ds->failed_flush_operations = stats->failed_ops[BLOCK_ACCT_FLUSH]; + ds->failed_unmap_operations = stats->failed_ops[BLOCK_ACCT_UNMAP]; + + ds->invalid_rd_operations = stats->invalid_ops[BLOCK_ACCT_READ]; + ds->invalid_wr_operations = stats->invalid_ops[BLOCK_ACCT_WRITE]; + ds->invalid_zone_append_operations = + stats->invalid_ops[BLOCK_ACCT_ZONE_APPEND]; + ds->invalid_flush_operations = + stats->invalid_ops[BLOCK_ACCT_FLUSH]; + ds->invalid_unmap_operations = stats->invalid_ops[BLOCK_ACCT_UNMAP]; + + ds->rd_merged = stats->merged[BLOCK_ACCT_READ]; + ds->wr_merged = stats->merged[BLOCK_ACCT_WRITE]; + ds->zone_append_merged = stats->merged[BLOCK_ACCT_ZONE_APPEND]; + ds->unmap_merged = stats->merged[BLOCK_ACCT_UNMAP]; + ds->flush_operations = stats->nr_ops[BLOCK_ACCT_FLUSH]; + ds->wr_total_time_ns = stats->total_time_ns[BLOCK_ACCT_WRITE]; + ds->zone_append_total_time_ns = + stats->total_time_ns[BLOCK_ACCT_ZONE_APPEND]; + ds->rd_total_time_ns = stats->total_time_ns[BLOCK_ACCT_READ]; + ds->flush_total_time_ns = stats->total_time_ns[BLOCK_ACCT_FLUSH]; + ds->unmap_total_time_ns = stats->total_time_ns[BLOCK_ACCT_UNMAP]; + + ds->has_idle_time_ns = stats->last_access_time_ns > 0; + if (ds->has_idle_time_ns) { + ds->idle_time_ns = block_acct_idle_time_ns(stats); + } - ds->account_invalid = stats->account_invalid; - ds->account_failed = stats->account_failed; + ds->account_invalid = stats->account_invalid; + ds->account_failed = stats->account_failed; + + hgram = stats->latency_histogram; + ds->rd_latency_histogram + = bdrv_latency_histogram_stats(&hgram[BLOCK_ACCT_READ]); + ds->wr_latency_histogram + = bdrv_latency_histogram_stats(&hgram[BLOCK_ACCT_WRITE]); + ds->zone_append_latency_histogram + = bdrv_latency_histogram_stats(&hgram[BLOCK_ACCT_ZONE_APPEND]); + ds->flush_latency_histogram + = bdrv_latency_histogram_stats(&hgram[BLOCK_ACCT_FLUSH]); + } while ((ts = block_acct_interval_next(stats, ts))) { BlockDeviceTimedStats *dev_stats = g_malloc0(sizeof(*dev_stats)); -- 2.53.0