From 65e73f38852c6289fc0e499cde7ab6d64514a554 Mon Sep 17 00:00:00 2001
From: Adam Kupczyk <akupczyk@redhat.com>
Date: Sat, 30 Jan 2021 12:57:05 +0100
Subject: [PATCH] os/bluestore: Add option to check BlueFS reads

Add option "bluefs_check_for_zeros" to check if there are any zero-filled page.
If so, reread data. It is known that sometimes BlueStore gets such pages.
See "bluestore_retry_disk_reads".

Signed-off-by: Adam Kupczyk <akupczyk@redhat.com>
(cherry picked from commit 7e495c57fe0ec8d8bdb1dbff90b177e656a22cbe)
---
 src/common/legacy_config_opts.h |   1 +
 src/common/options.cc           |   8 ++
 src/os/bluestore/BlueFS.cc      | 169 +++++++++++++++++++++++++++++++-
 src/os/bluestore/BlueFS.h       |  11 +++
 4 files changed, 185 insertions(+), 4 deletions(-)

diff --git a/src/common/legacy_config_opts.h b/src/common/legacy_config_opts.h
index d30c5fda8a985..5a0aa9545e270 100644
--- a/src/common/legacy_config_opts.h
+++ b/src/common/legacy_config_opts.h
@@ -909,6 +909,7 @@ OPTION(bluefs_allocator, OPT_STR)     // stupid | bitmap
 OPTION(bluefs_log_replay_check_allocations, OPT_BOOL)
 OPTION(bluefs_replay_recovery, OPT_BOOL)
 OPTION(bluefs_replay_recovery_disable_compact, OPT_BOOL)
+OPTION(bluefs_check_for_zeros, OPT_BOOL)
 
 OPTION(bluestore_bluefs, OPT_BOOL)
 OPTION(bluestore_bluefs_env_mirror, OPT_BOOL) // mirror to normal Env for debug
diff --git a/src/common/options.cc b/src/common/options.cc
index 774f263a1e4a7..f9c7f5870b131 100644
--- a/src/common/options.cc
+++ b/src/common/options.cc
@@ -4207,6 +4207,14 @@ std::vector<Option> get_global_options() {
     .set_default(false)
     .set_description(""),
 
+    Option("bluefs_check_for_zeros", Option::TYPE_BOOL, Option::LEVEL_DEV)
+    .set_default(false)
+    .set_flag(Option::FLAG_RUNTIME)
+    .set_description("Check data read for suspicious pages")
+    .set_long_description("Looks into data read to check if there is a 4K block entirely filled with zeros. "
+			  "If this happens, we re-read data. If there is difference, we print error to log.")
+    .add_see_also("bluestore_retry_disk_reads"),
+
     Option("bluestore_bluefs", Option::TYPE_BOOL, Option::LEVEL_DEV)
     .set_default(true)
     .set_flag(Option::FLAG_CREATE)
diff --git a/src/os/bluestore/BlueFS.cc b/src/os/bluestore/BlueFS.cc
index 8081b42e12bd5..4ac3f4c0d145d 100644
--- a/src/os/bluestore/BlueFS.cc
+++ b/src/os/bluestore/BlueFS.cc
@@ -91,6 +91,9 @@ public:
 	r = admin_socket->register_command("bluefs files list", hook,
 					   "print files in bluefs");
 	ceph_assert(r == 0);
+	r = admin_socket->register_command("bluefs debug_inject_read_zeros", hook,
+					   "Injects 8K zeros into next BlueFS read. Debug only.");
+	ceph_assert(r == 0);
       }
     }
     return hook;
@@ -170,6 +173,8 @@ private:
       }
       f->close_section();
       f->flush(out);
+    } else if (command == "bluefs debug_inject_read_zeros") {
+      bluefs->inject_read_zeros++;
     } else {
       errss << "Invalid command" << std::endl;
       return -ENOSYS;
@@ -290,6 +295,10 @@ void BlueFS::_init_logger()
   b.add_u64_counter(l_bluefs_read_prefetch_bytes, "read_prefetch_bytes",
 		    "Bytes requested in prefetch read mode", NULL,
 		    PerfCountersBuilder::PRIO_USEFUL, unit_t(UNIT_BYTES));
+  b.add_u64(l_bluefs_read_zeros_candidate, "read_zeros_candidate",
+	    "How many times bluefs read found page with all 0s");
+  b.add_u64(l_bluefs_read_zeros_errors, "read_zeros_errors",
+	    "How many times bluefs read found transient page with all 0s");
 
   logger = b.create_perf_counters();
   cct->get_perfcounters_collection()->add(logger);
@@ -606,6 +615,146 @@ void BlueFS::_stop_alloc()
   }
 }
 
+int BlueFS::read(uint8_t ndev, uint64_t off, uint64_t len,
+		 ceph::buffer::list *pbl, IOContext *ioc, bool buffered)
+{
+  dout(10) << __func__ << " dev " << int(ndev)
+           << ": 0x" << std::hex << off << "~" << len << std::dec
+	   << (buffered ? " buffered" : "")
+	   << dendl;
+  int r;
+  bufferlist bl;
+  r = bdev[ndev]->read(off, len, &bl, ioc, buffered);
+  if (r != 0) {
+    return r;
+  }
+  uint64_t block_size = bdev[ndev]->get_block_size();
+  if (inject_read_zeros) {
+    if (len >= block_size * 2) {
+      derr << __func__ << " injecting error, zeros at "
+	   << int(ndev) << ": 0x" << std::hex << (off + len / 2)
+	   << "~" << (block_size * 2) << std::dec << dendl;
+      //use beginning, replace 8K in the middle with zeros, use tail
+      bufferlist temp;
+      bl.splice(0, len / 2 - block_size, &temp);
+      temp.append(buffer::create(block_size * 2, 0));
+      bl.splice(block_size * 2, len / 2 - block_size, &temp);
+      bl = temp;
+      inject_read_zeros--;
+    }
+  }
+  //make a check if there is a block with all 0
+  uint64_t to_check_len = len;
+  uint64_t skip = p2nphase(off, block_size);
+  if (skip >= to_check_len) {
+    return r;
+  }
+  auto it = bl.begin(skip);
+  to_check_len -= skip;
+  bool all_zeros = false;
+  while (all_zeros == false && to_check_len >= block_size) {
+    // checking 0s step
+    unsigned block_left = block_size;
+    unsigned avail;
+    const char* data;
+    all_zeros = true;
+    while (all_zeros && block_left > 0) {
+      avail = it.get_ptr_and_advance(block_left, &data);
+      block_left -= avail;
+      all_zeros = mem_is_zero(data, avail);
+    }
+    // skipping step
+    while (block_left > 0) {
+      avail = it.get_ptr_and_advance(block_left, &data);
+      block_left -= avail;
+    }
+    to_check_len -= block_size;
+  }
+  if (all_zeros) {
+    logger->inc(l_bluefs_read_zeros_candidate, 1);
+    bufferlist bl_reread;
+    r = bdev[ndev]->read(off, len, &bl_reread, ioc, buffered);
+    if (r != 0) {
+      return r;
+    }
+    // check if both read gave the same
+    if (!bl.contents_equal(bl_reread)) {
+      // report problems to log, but continue, maybe it will be good now...
+      derr << __func__ << " initial read of " << int(ndev)
+	   << ": 0x" << std::hex << off << "~" << len
+	   << std::dec << ": different then re-read " << dendl;
+      logger->inc(l_bluefs_read_zeros_errors, 1);
+    }
+    // use second read will be better if is different
+    pbl->append(bl_reread);
+  } else {
+    pbl->append(bl);
+  }
+  return r;
+}
+
+int BlueFS::read_random(uint8_t ndev, uint64_t off, uint64_t len, char *buf, bool buffered)
+{
+  dout(10) << __func__ << " dev " << int(ndev)
+           << ": 0x" << std::hex << off << "~" << len << std::dec
+	   << (buffered ? " buffered" : "")
+	   << dendl;
+  int r;
+  r = bdev[ndev]->read_random(off, len, buf, buffered);
+  if (r != 0) {
+    return r;
+  }
+  uint64_t block_size = bdev[ndev]->get_block_size();
+  if (inject_read_zeros) {
+    if (len >= block_size * 2) {
+      derr << __func__ << " injecting error, zeros at "
+	   << int(ndev) << ": 0x" << std::hex << (off + len / 2)
+	   << "~" << (block_size * 2) << std::dec << dendl;
+      //zero middle 8K
+      memset(buf + len / 2 - block_size, 0, block_size * 2);
+      inject_read_zeros--;
+    }
+  }
+  //make a check if there is a block with all 0
+  uint64_t to_check_len = len;
+  const char* data = buf;
+  uint64_t skip = p2nphase(off, block_size);
+  if (skip >= to_check_len) {
+    return r;
+  }
+  to_check_len -= skip;
+  data += skip;
+
+  bool all_zeros = false;
+  while (all_zeros == false && to_check_len >= block_size) {
+    if (mem_is_zero(data, block_size)) {
+      // at least one block is all zeros
+      all_zeros = true;
+      break;
+    }
+    data += block_size;
+    to_check_len -= block_size;
+  }
+  if (all_zeros) {
+    logger->inc(l_bluefs_read_zeros_candidate, 1);
+    std::unique_ptr<char[]> data_reread(new char[len]);
+    r = bdev[ndev]->read_random(off, len, &data_reread[0], buffered);
+    if (r != 0) {
+      return r;
+    }
+    // check if both read gave the same
+    if (memcmp(buf, &data_reread[0], len) != 0) {
+      derr << __func__ << " initial read of " << int(ndev)
+	   << ": 0x" << std::hex << off << "~" << len
+	   << std::dec << ": different then re-read " << dendl;
+      logger->inc(l_bluefs_read_zeros_errors, 1);
+      // second read is probably better
+      memcpy(buf, &data_reread[0], len);
+    }
+  }
+  return r;
+}
+
 int BlueFS::mount()
 {
   dout(1) << __func__ << dendl;
@@ -1750,8 +1899,14 @@ int64_t BlueFS::_read_random(
       dout(20) << __func__ << " read random 0x"
 	       << std::hex << x_off << "~" << l << std::dec
 	       << " of " << *p << dendl;
-      int r = bdev[p->bdev]->read_random(p->offset + x_off, l, out,
-					 cct->_conf->bluefs_buffered_io);
+      int r;
+      if (!cct->_conf->bluefs_check_for_zeros) {
+	r = bdev[p->bdev]->read_random(p->offset + x_off, l, out,
+				       cct->_conf->bluefs_buffered_io);
+      } else {
+	r = read_random(p->bdev, p->offset + x_off, l, out,
+			cct->_conf->bluefs_buffered_io);
+      }
       ceph_assert(r == 0);
       off += l;
       len -= l;
@@ -1865,8 +2020,14 @@ int64_t BlueFS::_read(
         dout(20) << __func__ << " fetching 0x"
                  << std::hex << x_off << "~" << l << std::dec
                  << " of " << *p << dendl;
-        int r = bdev[p->bdev]->read(p->offset + x_off, l, &buf->bl, ioc[p->bdev],
-				    cct->_conf->bluefs_buffered_io);
+	int r;
+	if (!cct->_conf->bluefs_check_for_zeros) {
+	  r = bdev[p->bdev]->read(p->offset + x_off, l, &buf->bl, ioc[p->bdev],
+				  cct->_conf->bluefs_buffered_io);
+	} else {
+	  r = read(p->bdev, p->offset + x_off, l, &buf->bl, ioc[p->bdev],
+		   cct->_conf->bluefs_buffered_io);
+	}
         ceph_assert(r == 0);
       }
       u_lock.unlock();
diff --git a/src/os/bluestore/BlueFS.h b/src/os/bluestore/BlueFS.h
index 0f691adee2d02..72ffd3ff9bad0 100644
--- a/src/os/bluestore/BlueFS.h
+++ b/src/os/bluestore/BlueFS.h
@@ -49,6 +49,8 @@ enum {
   l_bluefs_read_bytes,
   l_bluefs_read_prefetch_count,
   l_bluefs_read_prefetch_bytes,
+  l_bluefs_read_zeros_candidate,
+  l_bluefs_read_zeros_errors,
 
   l_bluefs_last,
 };
@@ -347,6 +349,8 @@ private:
 
   class SocketHook;
   SocketHook* asok_hook = nullptr;
+  // used to trigger zeros into read (debug / verify)
+  std::atomic<uint64_t> inject_read_zeros{0};
 
   void _init_logger();
   void _shutdown_logger();
@@ -613,6 +617,13 @@ public:
   const PerfCounters* get_perf_counters() const {
     return logger;
   }
+
+private:
+  // Wrappers for BlockDevice::read(...) and BlockDevice::read_random(...)
+  // They are used for checking if read values are all 0, and reread if so.
+  int read(uint8_t ndev, uint64_t off, uint64_t len,
+	   ceph::buffer::list *pbl, IOContext *ioc, bool buffered);
+  int read_random(uint8_t ndev, uint64_t off, uint64_t len, char *buf, bool buffered);
 };
 
 class OriginalVolumeSelector : public BlueFSVolumeSelector {
-- 
2.39.5