[18.03] Fix deadlock introduced in bd613df2

[thaJeztah]

backport of #2180 for the bump_18.03 branch

git checkout -b 18.03-backport-fix-overlay-deadlock-regression upstream/bump_18.03
git cherry-pick -s -S -x 3755f80aa0b178acd0447585539a5c13072fe85e
git push -u origin

no conflicts

Commit bd613df prevented data corruption due to simultaneous
driver.CreateNetwork()/driver.DeleteNetwork() by holding the network
lock through the read/modify part of the operation. However, part of
the DeleteNetwork operation entails sending a message to the peerDB to
tell that goroutine to flush entries on deletion. This can lead to a
deadlock where:

• driver.DeleteNetwork() starts and acquires driver.Lock()
• peerDB receives some other request (e.g. EventNotify) and blocks
  on driver.Lock()
• driver.DeleteNetwork() attempts a peerDB flush and blocks waiting
  on the synchronous peerDB operation channel

This patch fixes the issue by deferring the peerDB flush operation until
after DeleteNetwork() unlocks driver.Lock(). Commit bd613df only
modified CreateNetwork() and DeleteNetwork() and the critical section
that driver.Lock() protects in CreateNetwork() does not perform any
peerDB notifications or other locks of driver data structures. So this
solution should be a complete fix for any regressions introduced in
bd613df.

Signed-off-by: Chris Telfer ctelfer@docker.com
(cherry picked from commit 3755f80)
Signed-off-by: Sebastiaan van Stijn github@gone.nl

[abhi]

LGTM

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (bump_18.03@3931ba4). Click here to learn what that means.
The diff coverage is 0%.

@@             Coverage Diff              @@
##             bump_18.03   #2182   +/-   ##
============================================
  Coverage              ?   40.6%           
============================================
  Files                 ?     139           
  Lines                 ?   22490           
  Branches              ?       0           
============================================
  Hits                  ?    9132           
  Misses                ?   12028           
  Partials              ?    1330

Impacted Files	Coverage Δ
drivers/overlay/ov_network.go	2.77% <0%> (ø)

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