pgsql: Drop slot's LWLock before returning from SaveSlotToPath()

Drop slot's LWLock before returning from SaveSlotToPath()

When SaveSlotToPath() is called with elevel=LOG, the early exits didn't
release the slot's io_in_progress_lock.

This could result in a walsender being stuck on the lock forever. A
possible way to get into this situation is if the offending code paths
are triggered in a low disk space situation.

Author: Pavan Deolasee <pavan(dot)deolasee(at)2ndquadrant(dot)com>
Reported-by: Craig Ringer <craig(at)2ndquadrant(dot)com>
Discussion: https://www.postgresql.org/message-id/flat/56a138c5-de61-f553-7e8f-6789296de785%402ndquadrant.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/49bf81536e242f079bfbce6e8f95f53f18207dd5

Modified Files
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src/backend/replication/slot.c | 10 ++++++++++
1 file changed, 10 insertions(+)