tree 40a881aaed9d2ede15b1290b3223a8e1291736e8
parent 10a76acb0f2564a525887f88c4e3aea10f3fc1f2
author David Benjamin <davidben@google.com> 1623873613 -0400
committer Boringssl LUCI CQ <boringssl-scoped@luci-project-accounts.iam.gserviceaccount.com> 1624496313 +0000

Reduce bouncing on the cache lock in ssl_update_cache.

ssl_update_cache takes the cache lock to add to the session cache,
releases it, and then immediately takes and releases the lock to
increment handshakes_since_cache_flush. Then, in 1/255 connections, does
the same thing again to flush stale sessions.

Merge the first two into one lock. In doing so, move ssl_update_cache to
ssl_session.cc, so it can access a newly-extracted add_session_lock.
Also remove the mode parameter (the SSL knows if it's a client or
server), and move the established_session != session check to the
caller, which more directly knows whether there was a new session.

Also add some TSan coverage for this path in the tests. In an earlier
iteration of this patch, I managed to introduce a double-locking bug
because we weren't testing it at all. Confirmed this test catches both
double-locking and insufficient locking. (It doesn't seem able to catch
using a read lock instead of a write lock in SSL_CTX_flush_sessions,
however. I suspect the hash table is distributing the cells each thread
touches.)

Update-Note: This reshuffles some locks around the session cache.
(Hopefully for the better.)

Change-Id: I78dca53fda74e036b90110cca7fbcc306a5c8ebe
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/48133
Commit-Queue: David Benjamin <davidben@google.com>
Reviewed-by: Adam Langley <agl@google.com>