Ensure empty error tables in scripts don't crash Valkey

[Fusl]

When calling the command EVAL error{} 0, Valkey crashes with the following stack trace. This patch ensures we never leave the err_info.msg field null when we fail to extract a proper error message.

=== VALKEY BUG REPORT START: Cut & paste starting from here ===
2595901:M 18 Jun 2025 01:20:12.917 # valkey 8.1.2 crashed by signal: 11, si_code: 1
2595901:M 18 Jun 2025 01:20:12.917 # Accessing address: (nil)
2595901:M 18 Jun 2025 01:20:12.917 # Crashed running the instruction at: 0x726f8e57ed1d

------ STACK TRACE ------
EIP:
/usr/lib/libc.so.6(+0x16ed1d) [0x726f8e57ed1d]

2595905 bio_aof
/usr/lib/libc.so.6(+0x9de22) [0x726f8e4ade22]
/usr/lib/libc.so.6(+0x91fda) [0x726f8e4a1fda]
/usr/lib/libc.so.6(+0x9264c) [0x726f8e4a264c]
/usr/lib/libc.so.6(pthread_cond_wait+0x14e) [0x726f8e4a4d1e]
valkey-server *:6379(bioProcessBackgroundJobs+0x1b4) [0x6530abb46db4]
/usr/lib/libc.so.6(+0x957eb) [0x726f8e4a57eb]
/usr/lib/libc.so.6(+0x11918c) [0x726f8e52918c]

2595904 bio_close_file
/usr/lib/libc.so.6(+0x9de22) [0x726f8e4ade22]
/usr/lib/libc.so.6(+0x91fda) [0x726f8e4a1fda]
/usr/lib/libc.so.6(+0x9264c) [0x726f8e4a264c]
/usr/lib/libc.so.6(pthread_cond_wait+0x14e) [0x726f8e4a4d1e]
valkey-server *:6379(bioProcessBackgroundJobs+0x1b4) [0x6530abb46db4]
/usr/lib/libc.so.6(+0x957eb) [0x726f8e4a57eb]
/usr/lib/libc.so.6(+0x11918c) [0x726f8e52918c]

2595901 valkey-server *
/usr/lib/libc.so.6(+0x3def0) [0x726f8e44def0]
/usr/lib/libc.so.6(+0x16ed1d) [0x726f8e57ed1d]
valkey-server *:6379(sdscatfmt+0x894) [0x6530abaa24a4]
valkey-server *:6379(luaCallFunction+0x39a) [0x6530abbc66ea]
valkey-server *:6379(+0x1a0992) [0x6530abbc6992]
valkey-server *:6379(scriptingEngineCallFunction+0x98) [0x6530abbc1298]
valkey-server *:6379(+0x11ff55) [0x6530abb45f55]
valkey-server *:6379(call+0x174) [0x6530aba94454]
valkey-server *:6379(processCommand+0x93d) [0x6530aba958dd]
valkey-server *:6379(processCommandAndResetClient+0x21) [0x6530abaa9d11]
valkey-server *:6379(processInputBuffer+0xe3) [0x6530abaaee83]
valkey-server *:6379(readQueryFromClient+0x65) [0x6530abaaef55]
valkey-server *:6379(+0x18e31a) [0x6530abbb431a]
valkey-server *:6379(aeProcessEvents+0x24a) [0x6530aba790ca]
valkey-server *:6379(aeMain+0x2d) [0x6530aba7938d]
valkey-server *:6379(main+0x3f6) [0x6530aba6e7b6]
/usr/lib/libc.so.6(+0x276b5) [0x726f8e4376b5]
/usr/lib/libc.so.6(__libc_start_main+0x89) [0x726f8e437769]
valkey-server *:6379(_start+0x25) [0x6530aba70235]

2595906 bio_lazy_free
/usr/lib/libc.so.6(+0x9de22) [0x726f8e4ade22]
/usr/lib/libc.so.6(+0x91fda) [0x726f8e4a1fda]
/usr/lib/libc.so.6(+0x9264c) [0x726f8e4a264c]
/usr/lib/libc.so.6(pthread_cond_wait+0x14e) [0x726f8e4a4d1e]
valkey-server *:6379(bioProcessBackgroundJobs+0x1b4) [0x6530abb46db4]
/usr/lib/libc.so.6(+0x957eb) [0x726f8e4a57eb]
/usr/lib/libc.so.6(+0x11918c) [0x726f8e52918c]

4/4 expected stacktraces.

------ STACK TRACE DONE ------

------ REGISTERS ------
2595901:M 18 Jun 2025 01:20:12.920 # 
RAX:0000000000000000 RBX:0000726f8dd35663
RCX:0000000000000000 RDX:0000000000000000
RDI:0000000000000000 RSI:0000000000000010
RBP:00007ffc2b821a80 RSP:00007ffc2b821938
R8 :000000000000000c R9 :00006530abc111b8
R10:0000000000000001 R11:0000000000000003
R12:00006530abc49adc R13:00006530abc111b7
R14:0000000000000001 R15:0000000000000001
RIP:0000726f8e57ed1d EFL:0000000000010283
CSGSFS:002b000000000033
2595901:M 18 Jun 2025 01:20:12.921 * hide-user-data-from-log is on, skip logging stack content to avoid spilling user data.

------ INFO OUTPUT ------
# Server
redis_version:7.2.4
server_name:valkey
valkey_version:8.1.2
valkey_release_stage:ga
redis_git_sha1:00000000
redis_git_dirty:0
redis_build_id:38d65aa7b4148d2c
server_mode:standalone
os:Linux 6.14.6-arch1-1 x86_64
arch_bits:64
monotonic_clock:POSIX clock_gettime
multiplexing_api:epoll
gcc_version:15.1.1
process_id:2595901
process_supervised:no
run_id:a0b75f67a217a81142f17553028c010e86c1ee80
tcp_port:6379
server_time_usec:1750209612917634
uptime_in_seconds:16
uptime_in_days:0
hz:10
configured_hz:10
clients_hz:10
lru_clock:5379148
executable:/home/fusl/valkey-server
config_file:
io_threads_active:0
availability_zone:
listener0:name=tcp,bind=*,bind=-::*,port=6379

# Clients
connected_clients:1
cluster_connections:0
maxclients:10000
client_recent_max_input_buffer:0
client_recent_max_output_buffer:0
blocked_clients:0
tracking_clients:0
pubsub_clients:0
watching_clients:0
clients_in_timeout_table:0
total_watched_keys:0
total_blocking_keys:0
total_blocking_keys_on_nokey:0
paused_reason:none
paused_actions:none
paused_timeout_milliseconds:0

# Memory
used_memory:911824
used_memory_human:890.45K
used_memory_rss:15323136
used_memory_rss_human:14.61M
used_memory_peak:911824
used_memory_peak_human:890.45K
used_memory_peak_perc:100.29%
used_memory_overhead:892232
used_memory_startup:891824
used_memory_dataset:19592
used_memory_dataset_perc:97.96%
allocator_allocated:1845952
allocator_active:1986560
allocator_resident:6672384
allocator_muzzy:0
total_system_memory:67323842560
total_system_memory_human:62.70G
used_memory_lua:34816
used_memory_vm_eval:34816
used_memory_lua_human:34.00K
used_memory_scripts_eval:184
number_of_cached_scripts:1
number_of_functions:0
number_of_libraries:0
used_memory_vm_functions:33792
used_memory_vm_total:68608
used_memory_vm_total_human:67.00K
used_memory_functions:224
used_memory_scripts:408
used_memory_scripts_human:408B
maxmemory:0
maxmemory_human:0B
maxmemory_policy:noeviction
allocator_frag_ratio:1.00
allocator_frag_bytes:0
allocator_rss_ratio:3.36
allocator_rss_bytes:4685824
rss_overhead_ratio:2.30
rss_overhead_bytes:8650752
mem_fragmentation_ratio:17.18
mem_fragmentation_bytes:14431168
mem_not_counted_for_evict:0
mem_replication_backlog:0
mem_total_replication_buffers:0
mem_clients_slaves:0
mem_clients_normal:0
mem_cluster_links:0
mem_aof_buffer:0
mem_allocator:jemalloc-5.3.0
mem_overhead_db_hashtable_rehashing:0
active_defrag_running:0
lazyfree_pending_objects:0
lazyfreed_objects:0

# Persistence
loading:0
async_loading:0
current_cow_peak:0
current_cow_size:0
current_cow_size_age:0
current_fork_perc:0.00
current_save_keys_processed:0
current_save_keys_total:0
rdb_changes_since_last_save:0
rdb_bgsave_in_progress:0
rdb_last_save_time:1750209596
rdb_last_bgsave_status:ok
rdb_last_bgsave_time_sec:-1
rdb_current_bgsave_time_sec:-1
rdb_saves:0
rdb_last_cow_size:0
rdb_last_load_keys_expired:0
rdb_last_load_keys_loaded:0
aof_enabled:0
aof_rewrite_in_progress:0
aof_rewrite_scheduled:0
aof_last_rewrite_time_sec:-1
aof_current_rewrite_time_sec:-1
aof_last_bgrewrite_status:ok
aof_rewrites:0
aof_rewrites_consecutive_failures:0
aof_last_write_status:ok
aof_last_cow_size:0
module_fork_in_progress:0
module_fork_last_cow_size:0

# Stats
total_connections_received:1
total_commands_processed:0
instantaneous_ops_per_sec:0
total_net_input_bytes:34
total_net_output_bytes:0
total_net_repl_input_bytes:0
total_net_repl_output_bytes:0
instantaneous_input_kbps:0.00
instantaneous_output_kbps:0.00
instantaneous_input_repl_kbps:0.00
instantaneous_output_repl_kbps:0.00
rejected_connections:0
sync_full:0
sync_partial_ok:0
sync_partial_err:0
expired_keys:0
expired_stale_perc:0.00
expired_time_cap_reached_count:0
expire_cycle_cpu_milliseconds:0
evicted_keys:0
evicted_clients:0
evicted_scripts:0
total_eviction_exceeded_time:0
current_eviction_exceeded_time:0
keyspace_hits:0
keyspace_misses:0
pubsub_channels:0
pubsub_patterns:0
pubsubshard_channels:0
latest_fork_usec:0
total_forks:0
migrate_cached_sockets:0
slave_expires_tracked_keys:0
active_defrag_hits:0
active_defrag_misses:0
active_defrag_key_hits:0
active_defrag_key_misses:0
total_active_defrag_time:0
current_active_defrag_time:0
tracking_total_keys:0
tracking_total_items:0
tracking_total_prefixes:0
unexpected_error_replies:0
total_error_replies:0
dump_payload_sanitizations:0
total_reads_processed:1
total_writes_processed:0
io_threaded_reads_processed:0
io_threaded_writes_processed:0
io_threaded_freed_objects:0
io_threaded_accept_processed:0
io_threaded_poll_processed:0
io_threaded_total_prefetch_batches:0
io_threaded_total_prefetch_entries:0
client_query_buffer_limit_disconnections:0
client_output_buffer_limit_disconnections:0
reply_buffer_shrinks:0
reply_buffer_expands:0
eventloop_cycles:170
eventloop_duration_sum:17739
eventloop_duration_cmd_sum:0
instantaneous_eventloop_cycles_per_sec:9
instantaneous_eventloop_duration_usec:99
acl_access_denied_auth:0
acl_access_denied_cmd:0
acl_access_denied_key:0
acl_access_denied_channel:0

# Replication
role:master
connected_slaves:0
replicas_waiting_psync:0
master_failover_state:no-failover
master_replid:d35a0bb7979f490a60174bb363524431d7eb2428
master_replid2:0000000000000000000000000000000000000000
master_repl_offset:0
second_repl_offset:-1
repl_backlog_active:0
repl_backlog_size:10485760
repl_backlog_first_byte_offset:0
repl_backlog_histlen:0

# CPU
used_cpu_sys:0.012543
used_cpu_user:0.016853
used_cpu_sys_children:0.000000
used_cpu_user_children:0.000000
used_cpu_sys_main_thread:0.012440
used_cpu_user_main_thread:0.016714

# Modules

# Commandstats

# Errorstats

# Latencystats

# Cluster
cluster_enabled:0

# Keyspace

------ CLIENT LIST OUTPUT ------
id=2 addr=127.0.0.1:41372 laddr=127.0.0.1:6379 fd=10 name=*redacted* age=0 idle=0 flags=N capa= db=0 sub=0 psub=0 ssub=0 multi=-1 watch=0 qbuf=0 qbuf-free=0 argv-mem=12 multi-mem=0 rbs=16384 rbp=16384 obl=0 oll=0 omem=0 tot-mem=17060 events=r cmd=eval user=*redacted* redir=-1 resp=2 lib-name= lib-ver= tot-net-in=34 tot-net-out=0 tot-cmds=0

------ CURRENT CLIENT INFO ------
id=2 addr=127.0.0.1:41372 laddr=127.0.0.1:6379 fd=10 name=*redacted* age=0 idle=0 flags=N capa= db=0 sub=0 psub=0 ssub=0 multi=-1 watch=0 qbuf=0 qbuf-free=0 argv-mem=12 multi-mem=0 rbs=16384 rbp=16384 obl=0 oll=0 omem=0 tot-mem=17060 events=r cmd=eval user=*redacted* redir=-1 resp=2 lib-name= lib-ver= tot-net-in=34 tot-net-out=0 tot-cmds=0
argc: 3
argv[0]: "eval"
argv[1]: 7 bytes
argv[2]: 1 bytes

------ EXECUTING CLIENT INFO ------
id=2 addr=127.0.0.1:41372 laddr=127.0.0.1:6379 fd=10 name=*redacted* age=0 idle=0 flags=N capa= db=0 sub=0 psub=0 ssub=0 multi=-1 watch=0 qbuf=0 qbuf-free=0 argv-mem=12 multi-mem=0 rbs=16384 rbp=16384 obl=0 oll=0 omem=0 tot-mem=17060 events=r cmd=eval user=*redacted* redir=-1 resp=2 lib-name= lib-ver= tot-net-in=34 tot-net-out=0 tot-cmds=0
argc: 3
argv[0]: "eval"
argv[1]: 7 bytes
argv[2]: 1 bytes

------ MODULES INFO OUTPUT ------

------ CONFIG DEBUG OUTPUT ------
repl-diskless-load disabled
debug-context ""
sanitize-dump-payload no
lazyfree-lazy-user-del yes
lazyfree-lazy-server-del yes
import-mode no
lazyfree-lazy-user-flush yes
list-compress-depth 0
dual-channel-replication-enabled no
repl-diskless-sync yes
activedefrag no
lazyfree-lazy-expire yes
io-threads 1
replica-read-only yes
client-query-buffer-limit 1gb
slave-read-only yes
lazyfree-lazy-eviction yes
proto-max-bulk-len 512mb

------ FAST MEMORY TEST ------
2595901:M 18 Jun 2025 01:20:12.921 # Bio worker thread #0 terminated
2595901:M 18 Jun 2025 01:20:12.921 # Bio worker thread #1 terminated
2595901:M 18 Jun 2025 01:20:12.921 # Bio worker thread #2 terminated
*** Preparing to test memory region 6530abce2000 (212992 bytes)
*** Preparing to test memory region 726f8af7f000 (2621440 bytes)
*** Preparing to test memory region 726f8b200000 (8388608 bytes)
*** Preparing to test memory region 726f8ba00000 (4194304 bytes)
*** Preparing to test memory region 726f8bffe000 (8388608 bytes)
*** Preparing to test memory region 726f8c7ff000 (8388608 bytes)
*** Preparing to test memory region 726f8d000000 (8388608 bytes)
*** Preparing to test memory region 726f8dc00000 (4194304 bytes)
*** Preparing to test memory region 726f8e290000 (16384 bytes)
*** Preparing to test memory region 726f8e3d2000 (20480 bytes)
*** Preparing to test memory region 726f8e5f8000 (32768 bytes)
*** Preparing to test memory region 726f8eb58000 (12288 bytes)
*** Preparing to test memory region 726f8eb5c000 (16384 bytes)
*** Preparing to test memory region 726f8ed63000 (4096 bytes)
*** Preparing to test memory region 726f8eef2000 (397312 bytes)
*** Preparing to test memory region 726f8efc7000 (4096 bytes)
.O.O.O.O.O.O.O.O.O.O.O.O.O.O.O.O
Fast memory test PASSED, however your memory can still be broken. Please run a memory test for several hours if possible.

------ DUMPING CODE AROUND EIP ------
Symbol: (null) (base: (nil))
Module: /usr/lib/libc.so.6 (base 0x726f8e410000)
$ xxd -r -p /tmp/dump.hex /tmp/dump.bin
$ objdump --adjust-vma=(nil) -D -b binary -m i386:x86-64 /tmp/dump.bin
------

=== VALKEY BUG REPORT END. Make sure to include from START to END. ===

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 71.59%. Comparing base (a05d1a6) to head (03f37f9).
⚠️ Report is 203 commits behind head on unstable.

Additional details and impacted files

@@             Coverage Diff              @@
##           unstable    #2229      +/-   ##
============================================
- Coverage     71.60%   71.59%   -0.02%     
============================================
  Files           123      123              
  Lines         66801    66803       +2     
============================================
- Hits          47833    47827       -6     
- Misses        18968    18976       +8     

Files with missing lines	Coverage Δ
src/lua/script_lua.c	89.76% <100.00%> (+0.02%)	⬆️

... and 12 files with indirect coverage changes

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• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
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[enjoy-binbin]

Good catch, do you know where it was introduced? I guess it was introduced in 7.0

[Fusl]

do you know where it was introduced?

According to git bisect, this bug was first introduced in Redis 7.0 RC2, specifically this PR.

[ranshid]

@Fusl can be please update the branch to the latest unstable after merging #2225 to verify the tests are no longer failing?

[soloestoy]

I wonder how did you track down this bug? The usage of 'lua error' in this context is not typical for business logic.

[Fusl]

how did you track down this bug?

I write complex Valkey eval scripts for a living. It's the only way to guarantee full atomicity with full flexibility when using Valkey as main database.

[ranshid]

LGTM

[zuiderkwast]

I write complex Valkey eval scripts for a living. It's the only way to guarantee full atomicity with full flexibility when using Valkey as main database.

This sounds interesting! Do you want to share some examples? Do you want to write a blog post?

[hpatro]

Nice finding @Fusl. TIL this exists. +1 to @zuiderkwast's request. Would be nice for the community to learn the best practices while writing scripts.