HDFS-16244.Add the necessary write lock in Checkpointer#doCheckpoint().

[jianghuazhu]

Description of PR

In Checkpointer#doCheckpoint(), when you need to execute reloadFromImageFile(), you need to add the necessary write lock.
Details: HDFS-16244

How was this patch tested?

Need to verify the correctness of Checkpointer#doCheckpoint().

[hadoop-yetus]

💔 -1 overall

Vote	Subsystem	Runtime	Logfile	Comment
+0 🆗	reexec	1m 3s		Docker mode activated.
			_ Prechecks _
+1 💚	dupname	0m 0s		No case conflicting files found.
+0 🆗	codespell	0m 0s		codespell was not available.
+1 💚	@author	0m 0s		The patch does not contain any @author tags.
-1 ❌	test4tests	0m 0s		The patch doesn't appear to include any new or modified tests. Please justify why no new tests are needed for this patch. Also please list what manual steps were performed to verify this patch.
			_ trunk Compile Tests _
+1 💚	mvninstall	35m 1s		trunk passed
+1 💚	compile	1m 24s		trunk passed with JDK Ubuntu-11.0.11+9-Ubuntu-0ubuntu2.20.04
+1 💚	compile	1m 16s		trunk passed with JDK Private Build-1.8.0_292-8u292-b10-0ubuntu1~20.04-b10
+1 💚	checkstyle	0m 58s		trunk passed
+1 💚	mvnsite	1m 25s		trunk passed
+1 💚	javadoc	0m 56s		trunk passed with JDK Ubuntu-11.0.11+9-Ubuntu-0ubuntu2.20.04
+1 💚	javadoc	1m 30s		trunk passed with JDK Private Build-1.8.0_292-8u292-b10-0ubuntu1~20.04-b10
+1 💚	spotbugs	3m 17s		trunk passed
+1 💚	shadedclient	24m 19s		branch has no errors when building and testing our client artifacts.
			_ Patch Compile Tests _
+1 💚	mvninstall	1m 12s		the patch passed
+1 💚	compile	1m 18s		the patch passed with JDK Ubuntu-11.0.11+9-Ubuntu-0ubuntu2.20.04
+1 💚	javac	1m 18s		the patch passed
+1 💚	compile	1m 9s		the patch passed with JDK Private Build-1.8.0_292-8u292-b10-0ubuntu1~20.04-b10
+1 💚	javac	1m 9s		the patch passed
+1 💚	blanks	0m 0s		The patch has no blanks issues.
+1 💚	checkstyle	0m 51s		the patch passed
+1 💚	mvnsite	1m 15s		the patch passed
+1 💚	javadoc	0m 49s		the patch passed with JDK Ubuntu-11.0.11+9-Ubuntu-0ubuntu2.20.04
+1 💚	javadoc	1m 25s		the patch passed with JDK Private Build-1.8.0_292-8u292-b10-0ubuntu1~20.04-b10
+1 💚	spotbugs	3m 21s		the patch passed
+1 💚	shadedclient	25m 6s		patch has no errors when building and testing our client artifacts.
			_ Other Tests _
-1 ❌	unit	381m 11s	/patch-unit-hadoop-hdfs-project_hadoop-hdfs.txt	hadoop-hdfs in the patch passed.
+1 💚	asflicense	1m 3s		The patch does not generate ASF License warnings.
		487m 21s

Reason	Tests
Failed junit tests	hadoop.hdfs.TestViewDistributedFileSystemWithMountLinks

Subsystem	Report/Notes
Docker	ClientAPI=1.41 ServerAPI=1.41 base: https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-3497/1/artifact/out/Dockerfile
GITHUB PR	#3497
Optional Tests	dupname asflicense compile javac javadoc mvninstall mvnsite unit shadedclient spotbugs checkstyle codespell
uname	Linux 38a7a93fc471 4.15.0-142-generic #146-Ubuntu SMP Tue Apr 13 01:11:19 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux
Build tool	maven
Personality	dev-support/bin/hadoop.sh
git revision	trunk / ba908b6
Default Java	Private Build-1.8.0_292-8u292-b10-0ubuntu1~20.04-b10
Multi-JDK versions	/usr/lib/jvm/java-11-openjdk-amd64:Ubuntu-11.0.11+9-Ubuntu-0ubuntu2.20.04 /usr/lib/jvm/java-8-openjdk-amd64:Private Build-1.8.0_292-8u292-b10-0ubuntu1~20.04-b10
Test Results	https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-3497/1/testReport/
Max. process+thread count	1901 (vs. ulimit of 5500)
modules	C: hadoop-hdfs-project/hadoop-hdfs U: hadoop-hdfs-project/hadoop-hdfs
Console output	https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-3497/1/console
versions	git=2.25.1 maven=3.6.3 spotbugs=4.2.2
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[jianghuazhu]

@jojochuang @virajjasani , here are some questions I hope to get your help.
I have resolved this issue (HDFS-16244), but I am not sure if more unit tests are needed here. If necessary, I will continue to work hard. I hope you can give some pointers.
thank you very much.

In addition, there are some exceptions in jenkins, such as:
TestMover
TestViewDistributedFileSystemWithMountLinks
It seems that these exceptions have little to do with the code I submitted.

[jojochuang]

LGTM
But do people still use backup node? IMO, it is deprecated and should be removed in the future.

[jianghuazhu]

Thanks @jojochuang for the comments and review.
I found this issue(HDFS-16244) by accident.
Yes, BackupNode is rarely used anymore. For the sake of system robustness, I propose this JIRA.

[jianghuazhu]

@ayushtkn @ferhui @Hexiaoqiao, can you take some time to review this pr.
thank you very much.

[virajjasani]

Makes sense, +1 (non-binding)

[virajjasani]

In addition, there are some exceptions in jenkins, such as: TestMover TestViewDistributedFileSystemWithMountLinks It seems that these exceptions have little to do with the code I submitted.

The failures in above tests are not relevant to this PR.

I have resolved this issue (HDFS-16244), but I am not sure if more unit tests are needed here. If necessary, I will continue to work hard. I hope you can give some pointers.

I doubt if this change can be unit tested, let's see what others recommend.

[jianghuazhu]

Thanks @virajjasani for the comment and review.

[jianghuazhu]

@ayushtkn @ferhui @Hexiaoqiao , are you willing to spend some time to help review this pr.
Thank you very much.

[ferhui]

@jianghuazhu Thanks for contribution. @virajjasani @jojochuang Thanks for review! Merged

[jianghuazhu]

@ferhui Thank you very much.