Otherwise we run into that:

Backtrace:
src/redis-server 127.0.0.1:21322(logStackTrace+0x45)[0x479035]
src/redis-server 127.0.0.1:21322(sigsegvHandler+0xb9)[0x4797f9]
/lib/x86_64-linux-gnu/libpthread.so.0(+0x11390)[0x7fd373c5e390]
src/redis-server 127.0.0.1:21322(_serverAssert+0x6a)[0x47660a]
src/redis-server 127.0.0.1:21322(freeReplicationBacklog+0x42)[0x451282]
src/redis-server 127.0.0.1:21322[0x4552d4]
src/redis-server 127.0.0.1:21322[0x4c5593]
src/redis-server 127.0.0.1:21322(aeProcessEvents+0x2e6)[0x42e786]
src/redis-server 127.0.0.1:21322(aeMain+0x1d)[0x42eb0d]
src/redis-server 127.0.0.1:21322(main+0x4c5)[0x42b145]
/lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xf0)[0x7fd3738a3830]
src/redis-server 127.0.0.1:21322(_start+0x29)[0x42b409]

Since we disconnect all the replicas and free the replication backlog in
certain replication paths, and the code that will free the replication
backlog expects that no replica is connected.

However we still need to free the replicas asynchronously in certain
cases, as documented in the top comment of disconnectSlaves().

Citing from the issue:

btw I suggest we change this fix to something else:
* We revert the fix.
* We add a call that disconnects chained replicas in the place where we trim the replica (that is a master i this case) offset.
This way we can avoid disconnections when there is no trimming of the backlog.

Note that we now want to disconnect replicas asynchronously in
disconnectSlaves(), because it's in general safer now that we can call
it from freeClient(). Otherwise for instance the command:

    CLIENT KILL TYPE master

May crash: clientCommand() starts running the linked of of clients,
looking for clients to kill. However it finds the master, kills it
calling freeClient(), but this in turn calls replicationCacheMaster()
that may also call disconnectSlaves() now. So the linked list iterator
of the clientCommand() will no longer be valid.

Implements sendfile for redis.

EAGAIN not handled for TLS during diskless load

Disconnect chained replicas when the replica performs PSYNC with the master always to avoid replication offset mismatch between master and chained replicas

Disconnect chained replicas when the replica performs PSYNC with the master always to avoid replication offset mismatch between master and chained replicas.

fix server crash for STRALGO command

Replace 'addDeferredMultiBulkLength' with 'addReplyDeferredLen' in comment

TLS: Improve tls-protocols clarity in redis.conf.

Fix reply bytes calculation error on 32bit platform

Fix #7275.

Tracking: flag CLIENT_TRACKING_BROKEN_REDIR when redir broken

fix a rare active defrag edge case bug leading to stagnation

There's a rare case which leads to stagnation in the defragger, causing
it to keep scanning the keyspace and do nothing (not moving any
allocation), this happens when all the allocator slabs of a certain bin
have the same % utilization, but the slab from which new allocations are
made have a lower utilization.

this commit fixes it by removing the current slab from the overall
average utilization of the bin, and also eliminate any precision loss in
the utilization calculation and move the decision about the defrag to
reside inside jemalloc.

and also add a test that consistently reproduce this issue.

also support:
  debug mallctl-str thread.tcache.flush VOID

fix clear USER_FLAG_ALLCOMMANDS flag in acl

Redis Benchmark: make test data better

Redis-Benchmark: avoid potentical memmory leaking

Tcl client support hash tagged keys.

in ACLSetUserCommandBit, when the command bit overflows, no operation
is performed, so no need clear the USER_FLAG_ALLCOMMANDS flag.

in ACLSetUser, when adding subcommand, we don't need to call
ACLGetCommandID ahead since subcommand may be empty.

The function of generating random data is designed by antirez. See #7196.

Use dictSize to get the size of dict in dict.c

Converge hash validation for adding and removing

Redis-cli 6.0.1 `--cluster-yes` doesn't work (fix #7246)

fix valgrind test failure in replication test

in b4416280 i added more keys to that test to make it run longer
but in valgrind this now means the test times out, give valgrind more
time.

add regression test for the race in #7205

with the original version of 6.0.0, this test detects an excessive full
sync.
with the fix in 1a7cd2c0, this test detects memory corruption,
especially when using libc allocator with or without valgrind.

This was broken in 1a7cd2c0: we identified a crash in the CI, what
was happening before the fix should be like that:

1. The client gets in the async free list.
2. However freeClient() gets called again against the same client
   which is a master.
3. The client arrived in freeClient() with the CLOSE_ASAP flag set.
4. The master gets cached, but NOT removed from the CLOSE_ASAP linked
   list.
5. The master client that was cached was immediately removed since it
   was still in the list.
6. Redis accessed a freed cached master.

This is how the crash looked like:

=== REDIS BUG REPORT START: Cut & paste starting from here ===
1092:S 16 May 2020 11:44:09.731 # Redis 999.999.999 crashed by signal: 11
1092:S 16 May 2020 11:44:09.731 # Crashed running the instruction at: 0x447e18
1092:S 16 May 2020 11:44:09.731 # Accessing address: 0xffffffffffffffff
1092:S 16 May 2020 11:44:09.731 # Failed assertion:  (:0)

------ STACK TRACE ------
EIP:
src/redis-server 127.0.0.1:21300(readQueryFromClient+0x48)[0x447e18]

And the 0xffff address access likely comes from accessing an SDS that is
set to NULL (we go -1 offset to read the header).