From b4aebc839a1a4dc87275739d0d2c85504074e036 Mon Sep 17 00:00:00 2001
From: Nikos Gorogiannis <nikosg@meta.com>
Date: Fri, 13 Dec 2024 08:31:37 -0800
Subject: [PATCH] [multicore] avoid racing on chdir

Summary:
In multicore we can't allow the workers to change the working directory concurrently in `Utils.do_in_dir` as they will eventually execute their functions in the wrong directory.

This diff introduces a mutex for exclusion, and removes redundant uses of the function which can crash due to recursively locking the mutex.

Reviewed By: jvillard

Differential Revision:
D67195918

Privacy Context Container: L1208441

fbshipit-source-id: 6f7c3518fbc9b638e8a5e71fa15bf4ce621ffe22
---
 infer/src/base/DBWriter.ml | 10 +++++-----
 infer/src/base/Utils.ml    |  9 ++++++---
 infer/src/base/Utils.mli   |  3 ++-
 3 files changed, 13 insertions(+), 9 deletions(-)

diff --git a/infer/src/base/DBWriter.ml b/infer/src/base/DBWriter.ml
index b538a58f62..0ba47fb9ef 100644
--- a/infer/src/base/DBWriter.ml
+++ b/infer/src/base/DBWriter.ml
@@ -12,6 +12,8 @@ module F = Format
 module ServerSocket = struct
   let socket_name = ResultsDirEntryName.db_writer_socket_name
 
+  let socket_path = Config.toplevel_results_dir ^/ socket_name
+
   let socket_addr = Unix.ADDR_UNIX socket_name
 
   let socket_domain = Unix.domain_of_sockaddr socket_addr
@@ -22,7 +24,7 @@ module ServerSocket = struct
       function. *)
   let in_results_dir ~f = Utils.do_in_dir ~dir:Config.toplevel_results_dir ~f
 
-  let socket_exists () = in_results_dir ~f:(fun () -> Sys.file_exists_exn socket_name)
+  let socket_exists () = Sys.file_exists_exn socket_path
 
   (* Error recuperation is done by attempting this function at module initialization time, and
      not using DbWriter at all in case it fails. See {!can_use_socket} below. *)
@@ -37,12 +39,10 @@ module ServerSocket = struct
     socket
 
 
-  let remove_socket_file () =
-    in_results_dir ~f:(fun () -> if socket_exists () then Unix.unlink socket_name)
-
+  let remove_socket_file () = if socket_exists () then Unix.unlink socket_path
 
   let remove_socket socket =
-    in_results_dir ~f:(fun () -> Unix.close socket) ;
+    Unix.close socket ;
     remove_socket_file ()
 
 
diff --git a/infer/src/base/Utils.ml b/infer/src/base/Utils.ml
index f35b0d8f55..a8e7bf42ae 100644
--- a/infer/src/base/Utils.ml
+++ b/infer/src/base/Utils.ml
@@ -435,10 +435,13 @@ let timeit ~f =
   (ret_val, duration)
 
 
+let mutex = Error_checking_mutex.create ()
+
 let do_in_dir ~dir ~f =
-  let cwd = Unix.getcwd () in
-  Unix.chdir dir ;
-  Exception.try_finally ~f ~finally:(fun () -> Unix.chdir cwd)
+  Error_checking_mutex.critical_section mutex ~f:(fun () ->
+      let cwd = Unix.getcwd () in
+      Unix.chdir dir ;
+      Exception.try_finally ~f ~finally:(fun () -> Unix.chdir cwd) )
 
 
 let get_available_memory_MB () =
diff --git a/infer/src/base/Utils.mli b/infer/src/base/Utils.mli
index c36392e5d1..b2e27397f4 100644
--- a/infer/src/base/Utils.mli
+++ b/infer/src/base/Utils.mli
@@ -127,7 +127,8 @@ val timeit : f:(unit -> 'a) -> 'a * Mtime.Span.t
 (** Returns the execution time of [f] together with its result *)
 
 val do_in_dir : dir:string -> f:(unit -> 'a) -> 'a
-(** executes [f] after cding into [dir] and then restores original cwd *)
+(** executes [f] after cding into [dir] and then restores original cwd. Uses a mutex to prevent
+    races on [chdir] in multicore mode. *)
 
 val get_available_memory_MB : unit -> int option
 (** On Linux systems, return [Some x] where [MemAvailable x] is in [/proc/meminfo]. Returns [None]