From 53f6aba3e6e63f7f993bf5c11cdaffab0dc24753 Mon Sep 17 00:00:00 2001
From: Vitaliy Filippov <vitalif@yourcmc.ru>
Date: Sun, 24 May 2020 17:22:12 +0300
Subject: [PATCH] Die when journal_sector_buffer_count is too small

---
 blockstore_journal.cpp | 20 ++++++++++++++++----
 blockstore_journal.h   |  2 +-
 osd_primary_subops.cpp |  2 ++
 3 files changed, 19 insertions(+), 5 deletions(-)

diff --git a/blockstore_journal.cpp b/blockstore_journal.cpp
index c4684bb3..21e70f50 100644
--- a/blockstore_journal.cpp
+++ b/blockstore_journal.cpp
@@ -6,18 +6,24 @@ blockstore_journal_check_t::blockstore_journal_check_t(blockstore_impl_t *bs)
     sectors_required = 0;
     next_pos = bs->journal.next_free;
     next_sector = bs->journal.cur_sector;
+    first_sector = -1;
     next_in_pos = bs->journal.in_sector_pos;
     right_dir = next_pos >= bs->journal.used_start;
 }
 
 // Check if we can write <required> entries of <size> bytes and <data_after> data bytes after them to the journal
-int blockstore_journal_check_t::check_available(blockstore_op_t *op, int required, int size, int data_after)
+int blockstore_journal_check_t::check_available(blockstore_op_t *op, int entries_required, int size, int data_after)
 {
+    int required = entries_required;
     while (1)
     {
         int fits = (bs->journal.block_size - next_in_pos) / size;
         if (fits > 0)
         {
+            if (first_sector == -1)
+            {
+                first_sector = next_sector;
+            }
             required -= fits;
             next_in_pos += fits * size;
             sectors_required++;
@@ -38,10 +44,15 @@ int blockstore_journal_check_t::check_available(blockstore_op_t *op, int require
             right_dir = false;
         }
         next_in_pos = 0;
-        if (bs->journal.sector_info[next_sector].usage_count > 0 ||
-            bs->journal.sector_info[next_sector].dirty)
+        next_sector = ((next_sector + 1) % bs->journal.sector_count);
+        if (next_sector == first_sector)
         {
-            next_sector = ((next_sector + 1) % bs->journal.sector_count);
+            // next_sector may wrap when all sectors are flushed and the incoming batch is too big
+            // This is an error condition, we can't wait for anything in this case
+            throw std::runtime_error(
+                "Blockstore journal_sector_buffer_count="+std::to_string(bs->journal.sector_count)+
+                " is too small for a batch of "+std::to_string(entries_required)+" entries of "+std::to_string(size)+" bytes"
+            );
         }
         if (bs->journal.sector_info[next_sector].usage_count > 0 ||
             bs->journal.sector_info[next_sector].dirty)
@@ -107,6 +118,7 @@ journal_entry* prefill_single_journal_entry(journal_t & journal, uint16_t type,
         {
             // Also select next sector buffer in memory
             journal.cur_sector = ((journal.cur_sector + 1) % journal.sector_count);
+            assert(!journal.sector_info[journal.cur_sector].usage_count);
         }
         else
         {
diff --git a/blockstore_journal.h b/blockstore_journal.h
index c3cf6157..ef6af539 100644
--- a/blockstore_journal.h
+++ b/blockstore_journal.h
@@ -166,7 +166,7 @@ struct blockstore_journal_check_t
 {
     blockstore_impl_t *bs;
     uint64_t next_pos, next_sector, next_in_pos;
-    int sectors_required;
+    int sectors_required, first_sector;
     bool right_dir; // writing to the end or the beginning of the ring buffer
 
     blockstore_journal_check_t(blockstore_impl_t *bs);
diff --git a/osd_primary_subops.cpp b/osd_primary_subops.cpp
index 0e78cc4b..ec7ebe21 100644
--- a/osd_primary_subops.cpp
+++ b/osd_primary_subops.cpp
@@ -2,6 +2,8 @@
 
 void osd_t::autosync()
 {
+    // FIXME Autosync based on the number of unstable writes to prevent
+    // "journal_sector_buffer_count is too low for this batch" errors
     if (immediate_commit != IMMEDIATE_ALL && !autosync_op)
     {
         autosync_op = new osd_op_t();