branches/zip: Fix two bugs.

mtr_commit(): Do not acquire the log mutex if no log records are to be written.

ibuf_set_free_bits_func(): Do not clear mtr.modifications, because that would
prevent the dirty insert buffer bitmap block from being moved to the flush
list.  Instead, assume that mtr_commit() will not acquire log_sys->mutex
because redo logging is disabled.

buf_page_init_for_read(): I/O-fix the block before buf_buddy_alloc(), because
the newly allocated block could otherwise be reused by the compressed page.

buf/buf0buf.c

@@ -2440,6 +2440,7 @@ err_exit2:
 		io-handler thread. */
 
 		rw_lock_x_lock_gen(&block->lock, BUF_IO_READ);
+		buf_page_set_io_fix(bpage, BUF_IO_READ);
 
 		if (UNIV_UNLIKELY(zip_size)) {
 			page_zip_set_size(&block->page.zip, zip_size);
@@ -2458,8 +2459,6 @@ err_exit2:
 			block->page.zip.data = data;
 		}
 
-		buf_page_set_io_fix(bpage, BUF_IO_READ);
-
 		mutex_exit(&block->mutex);
 	} else {
 		/* Defer buf_buddy_alloc() until after the block has

ibuf/ibuf0ibuf.c

@@ -860,6 +860,11 @@ ibuf_set_free_bits_func(
 	mtr_start(&mtr);
 
 	if (recv_recovery_is_on()) {
+		/* Do not write to the redo log, because there is
+		crash recovery in progress.  Flushing the log would
+		require the possession of log_sys->mutex, which is
+		being held by the main thread. */
+
 		mtr_set_log_mode(&mtr, MTR_LOG_NONE);
 	}
 
@@ -896,14 +901,6 @@ ibuf_set_free_bits_func(
 #endif /* UNIV_IBUF_DEBUG */
 	ibuf_bitmap_page_set_bits(bitmap_page, page_no, zip_size,
 				  IBUF_BITMAP_FREE, val, &mtr);
-
-	if (recv_recovery_is_on()) {
-		/* Do not acquire log_sys->mutex or attempt to
-		write to the redo log, because the lock is being
-		held by the crash recovery thread. */
-		mtr.modifications = FALSE;
-	}
-
 	mtr_commit(&mtr);
 }
 

mtr/mtr0mtr.c

@@ -167,13 +167,17 @@ mtr_commit(
 /*=======*/
 	mtr_t*	mtr)	/* in: mini-transaction */
 {
+	ibool		write_log;
+
 	ut_ad(mtr);
 	ut_ad(mtr->magic_n == MTR_MAGIC_N);
 	ut_ad(mtr->state == MTR_ACTIVE);
 #ifdef UNIV_DEBUG
 	mtr->state = MTR_COMMITTING;
 #endif
-	if (mtr->modifications) {
+	write_log = mtr->modifications && mtr->n_log_recs;
+
+	if (write_log) {
 		mtr_log_reserve_and_write(mtr);
 	}
 
@@ -187,7 +191,7 @@ mtr_commit(
 
 	mtr_memo_pop_all(mtr);
 
-	if (mtr->modifications) {
+	if (write_log) {
 		log_release();
 	}