tsan: update docs

[dvyukov]

Summary

update docs for no_sanitize_thread attribute and blacklist

[samsonov]

docs/ThreadSanitizer.rst

109

Please double check this. Is it not the case that frontend drops sanitize_thread attribute from function
if it is blacklisted? In this case it can't be inlined into another function.

[dvyukov]

docs/ThreadSanitizer.rst

109

Yes, it seems to be the case.
PTAL

[samsonov]

LGTM

[Eugene.Zelenko]

Committed in r192872.

docs/LanguageExtensions.rst

 ----------------
 
 Use ``__has_feature(thread_sanitizer)`` to check if the code is being built
 with :doc:`ThreadSanitizer`.
 
 Use ``__attribute__((no_sanitize_thread))`` on a function declaration
 to specify that checks for data races on plain (non-atomic) memory accesses
 should not be inserted by ThreadSanitizer.
-The function may still be instrumented by the tool
-to avoid false positives in other places.
+The function is still instrumented by the tool to avoid false positives and
+provide meaningful stack traces.
 
 .. _langext-memory_sanitizer:
 
 MemorySanitizer
 ----------------
 Use ``__has_feature(memory_sanitizer)`` to check if the code is being built
 with :doc:`MemorySanitizer`.
 

docs/ThreadSanitizer.rst

 
 ``__attribute__((no_sanitize_thread))``
 -----------------------------------------------
 
 Some code should not be instrumented by ThreadSanitizer.
 One may use the function attribute
 :ref:`no_sanitize_thread <langext-thread_sanitizer>`
 to disable instrumentation of plain (non-atomic) loads/stores in a particular function.
-ThreadSanitizer may still instrument such functions to avoid false positives.
+ThreadSanitizer still instruments such functions to avoid false positives and
+provide meaningful stack traces.
 This attribute may not be
 supported by other compilers, so we suggest to use it together with
 ``__has_feature(thread_sanitizer)``.
 
 Blacklist
 ---------
 
 ThreadSanitizer supports ``src`` and ``fun`` entity types in
 :doc:`SanitizerSpecialCaseList`, that can be used to suppress data race reports in
-the specified source files or functions.
+the specified source files or functions. Unlike functions marked with
+:ref:`no_sanitize_thread <langext-thread_sanitizer>` attribute,
+blacklisted functions are not instrumented at all. This can lead to false positives
+due to missed synchronization via atomic operations and missed stack frames in reports.
 
 Limitations
 -----------
 
 * ThreadSanitizer uses more real memory than a native run. At the default
   settings the memory overhead is 5x plus 1Mb per each thread. Settings with 3x
   (less accurate analysis) and 9x (more accurate analysis) overhead are also
   available.
 * ThreadSanitizer maps (but does not reserve) a lot of virtual address space.