curvefs/mds: fix deadlock in UpdateClientAliveTime

[surpassly]

What problem does this PR solve?

Fix deadlock caused by UmontFs and UpdateClientAliveTime

Issue Number: #2308

Problem Summary: A deadlock happens when two bthread block each other.

What is changed and how it works?

What's Changed: Change the functions UpdateClientAliveTime and RefreshSession

How it Works: Make sure that the program acquires NameLock before WriteLock

Side effects(Breaking backward compatibility? Performance regression?): Unknown

Check List

• Relevant documentation/comments is changed or added
• I acknowledge that all my contributions will be made under the project's license

[Cyber-SiKu]

cicheck

[surpassly]

cicheck

[SeanHai]

1. There is no NameLock acquires in function 'AddMountPoint', so now there is no deadlock in the code, but NameLock really need added in.
2. If deal with AddMountPoint in RefreshSession, the third param 'addMountPoint' of functon 'UpdateClientAliveTime' is needn't.
3. The code you fixed in 'RefreshSession' still have some issues, if a UmountFs request get namelock and wait for WriteLock and another refresh session request get ReadLock here，then UmountFs request finished and this request will add mountpoint to the file which have umounted.

bool found;
{
ReadLockGuard rlock(recorderMutex_);
auto iter = mpTimeRecorder_.find(mountpath);
found = (iter == mpTimeRecorder_.end());
}
if (!found) {
// client hang timeout and recover later
// need add mountpoint to fsInfo
AddMountPoint(request->mountpoint(), request->fsname());
} else {
// update this client's alive time
UpdateClientAliveTime(request->mountpoint(), request->fsname(), false);
}

[surpassly]

1. There is no NameLock acquires in function 'AddMountPoint', so now there is no deadlock in the code, but NameLock really need added in.
2. If deal with AddMountPoint in RefreshSession, the third param 'addMountPoint' of functon 'UpdateClientAliveTime' is needn't.
3. The code you fixed in 'RefreshSession' still have some issues, if a UmountFs request get namelock and wait for WriteLock and another refresh session request get ReadLock here，then UmountFs request finished and this request will add mountpoint to the file which have umounted.

bool found; { ReadLockGuard rlock(recorderMutex_); auto iter = mpTimeRecorder_.find(mountpath); found = (iter == mpTimeRecorder_.end()); } if (!found) { // client hang timeout and recover later // need add mountpoint to fsInfo AddMountPoint(request->mountpoint(), request->fsname()); } else { // update this client's alive time UpdateClientAliveTime(request->mountpoint(), request->fsname(), false); }

I see, I closed this PR for now, maybe revisit it for future improvements.