[pgpool-committers: 5415] pgpool: Fix Pgpool child segfault in a race condition.

[Tatsuo Ishii]

Fix Pgpool child segfault in a race condition.

1) frontend tries to connect to Pgpool-II

2) there's no existing connection cache

3) try to create new backend connections by calling connect_backend()

4) inside connect_backend(), pool_create_cp() gets called

5) pool_create_cp() calls new_connection()

6) failover occurs and the global backend status is set to down, but
   the pgpool main does not send kill signal to the child process yet

7) inside new_connection() after checking VALID_BACKEND, it checks the
   global backend status and finds it is set to down status, so that
   it returns without creating new connection slot

8) connect_backend() continues and accesses the down connection slot
   because local status says it's alive, which results in a segfault.

Since there's already checking for the global status in
new_connection(), a fix could be syncing the local status with the
global status there.

See [pgpool-hackers: 3214] for discussion.

Branch
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V4_0_STABLE

Details
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https://git.postgresql.org/gitweb?p=pgpool2.git;a=commitdiff;h=5234b6e46091abd3f7c07772598cc63a83c6bd53

Modified Files
--------------
src/protocol/pool_connection_pool.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)