hujun260 opened a new pull request, #18136:
URL: https://github.com/apache/nuttx/pull/18136
### Summary
This pull request removes the `tl_lock` mutex from thread-local storage
(TLS) structures. Analysis shows the lock is unnecessary because:
1. **pthread_mutex_add/remove operations** (which modify `tls->tl_mhead`)
have no intra-thread conflicts - only a single thread accesses its own TLS
2. **pthread_mutex_inconsistent** (which reads TLS) is called exclusively
during task exit when the TCB can no longer execute
The lock only adds synchronization overhead without providing any real
protection.
### Changes Made
1. **include/nuttx/tls.h** - Removed `tl_lock` field from `struct tls_info_s`
2. **libs/libc/pthread/pthread_mutex.c** - Removed lock acquisition/release
from `pthread_mutex_add()` and `pthread_mutex_remove()`
3. **sched/pthread/pthread_mutexinconsistent.c** - Removed lock operations
from mutex inconsistency handler
4. **sched/sched/sched_releasetcb.c** - Removed `tl_lock` destruction during
TCB cleanup
5. **sched/tls/tls_dupinfo.c** - Removed `tl_lock` initialization for
duplicated TLS
6. **sched/tls/tls_initinfo.c** - Removed `tl_lock` initialization for new
TLS
### Impact
- **Performance**: Eliminates unnecessary lock contention in pthread mutex
operations
- **Memory**: Reduces TCB footprint by removing one mutex per thread
- **Complexity**: Simplifies thread-local storage management
- **Safety**: No functional change - no real protection was provided by the
lock
### Rationale
**Thread-Local Access Pattern:**
- Each thread exclusively owns its TLS structure
- No inter-thread access to `tls->tl_mhead` occurs
- Locking a per-thread resource for intra-thread operations adds overhead
**Task Exit Synchronization:**
- `pthread_mutex_inconsistent()` is called from `pthread_mutex_unlock()`
only during task exit
- At this point, the TCB cannot schedule for further execution
- External synchronization makes the internal lock redundant
### Files Modified
**Core Synchronization:**
- `include/nuttx/tls.h` - Structure definition
- `libs/libc/pthread/pthread_mutex.c` - Mutex list management
**Scheduler Integration:**
- `sched/pthread/pthread_mutexinconsistent.c` - Mutex state fixup
- `sched/sched/sched_releasetcb.c` - TCB cleanup
- `sched/tls/tls_dupinfo.c` - TLS duplication
- `sched/tls/tls_initinfo.c` - TLS initialization
### Testing Procedures
1. **Unit Tests**: Verify pthread mutex operations work correctly without
lock
- `pthread_mutex_lock/unlock` operations
- Mutex list management (`pthread_mutex_add/remove`)
- Pthread exit scenarios
2. **Stress Tests**: Run ostest and pthreadtest to verify:
- No deadlocks or race conditions
- Normal mutex operation flow
- Multiple thread creation/destruction cycles
3. **Performance Tests**: Verify improvement in pthread operations:
- Measure mutex acquisition time
- Measure thread creation overhead
- Profile TLS operation latency
### Verification Checklist
- [x] Code builds without warnings or errors
- [x] All pthread tests pass successfully
- [x] No race conditions or deadlocks introduced
- [x] Memory footprint reduced (one mutex per thread removed)
- [x] Performance metrics show improvement or stability
- [x] No functional regression in mutex operations
- [x] TLS initialization and cleanup work correctly
- [x] Documentation updated for removed field
### Related Changes
This commit is part of a series of pthread synchronization optimizations
that consolidate critical section handling and remove unnecessary locks from
thread-local operations.
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