Re: [PATCH 2/3] lto-plugin: make claim_file_handler thread-safe

["Martin Liška" <mliska@suse.cz>]

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On 6/21/22 09:56, Richard Biener wrote:
> On Mon, Jun 20, 2022 at 12:20 PM Martin Liška <mliska@suse.cz> wrote:
>>
>> On 6/20/22 11:32, Richard Biener wrote:
>>> On Thu, Jun 16, 2022 at 9:01 AM Martin Liška <mliska@suse.cz> wrote:
>>>>
>>>> lto-plugin/ChangeLog:
>>>>
>>>>         * lto-plugin.c (plugin_lock): New lock.
>>>>         (claim_file_handler): Use mutex for critical section.
>>>>         (onload): Initialize mutex.
>>>> ---
>>>>  lto-plugin/lto-plugin.c | 16 +++++++++++++++-
>>>>  1 file changed, 15 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/lto-plugin/lto-plugin.c b/lto-plugin/lto-plugin.c
>>>> index 00b760636dc..13118c4983c 100644
>>>> --- a/lto-plugin/lto-plugin.c
>>>> +++ b/lto-plugin/lto-plugin.c
>>>> @@ -55,6 +55,7 @@ along with this program; see the file COPYING3.  If not see
>>>>  #include <unistd.h>
>>>>  #include <fcntl.h>
>>>>  #include <sys/types.h>
>>>> +#include <pthread.h>
>>>
>>> Not sure if we support any non-pthread target for building the LTO
>>> plugin, but it
>>> seems we have
>>>
>>>   # Among non-ELF, only Windows platforms support the lto-plugin so far.
>>>   # Build it unless LTO was explicitly disabled.
>>>   case $target in
>>>     *-cygwin* | *-mingw*) build_lto_plugin=$enable_lto ;;
>>>
>>> which suggests that at least build validating the above with --enable-lto
>>
>> Verified that it's fine.
>>
>>>
>>> IIRC we have gthr-*.h in libgcc/, not sure if that's usable in a
>>> host linker plugin.
>>>
>>>>  #ifdef HAVE_SYS_WAIT_H
>>>>  #include <sys/wait.h>
>>>>  #endif
>>>> @@ -157,6 +158,9 @@ enum symbol_style
>>>>    ss_uscore,   /* Underscore prefix all symbols.  */
>>>>  };
>>>>
>>>> +/* Plug-in mutex.  */
>>>> +static pthread_mutex_t plugin_lock;
>>>> +
>>>>  static char *arguments_file_name;
>>>>  static ld_plugin_register_claim_file register_claim_file;
>>>>  static ld_plugin_register_all_symbols_read register_all_symbols_read;
>>>> @@ -1262,15 +1266,18 @@ claim_file_handler (const struct ld_plugin_input_file *file, int *claimed)
>>>>                               lto_file.symtab.syms);
>>>>        check (status == LDPS_OK, LDPL_FATAL, "could not add symbols");
>>>>
>>>> +      pthread_mutex_lock (&plugin_lock);
>>>>        num_claimed_files++;
>>>>        claimed_files =
>>>>         xrealloc (claimed_files,
>>>>                   num_claimed_files * sizeof (struct plugin_file_info));
>>>>        claimed_files[num_claimed_files - 1] = lto_file;
>>>> +      pthread_mutex_unlock (&plugin_lock);
>>>>
>>>>        *claimed = 1;
>>>>      }
>>>>
>>>> +  pthread_mutex_lock (&plugin_lock);
>>>>    if (offload_files == NULL)
>>>>      {
>>>>        /* Add dummy item to the start of the list.  */
>>>> @@ -1333,11 +1340,12 @@ claim_file_handler (const struct ld_plugin_input_file *file, int *claimed)
>>>>         offload_files_last_lto = ofld;
>>>>        num_offload_files++;
>>>>      }
>>>> +  pthread_mutex_unlock (&plugin_lock);
>>>>
>>>>    goto cleanup;
>>>>
>>>>   err:
>>>> -  non_claimed_files++;
>>>> +  __atomic_fetch_add (&non_claimed_files, 1, __ATOMIC_RELAXED);
>>>
>>> is it worth "optimizing" this with yet another need for target specific support
>>> (just use pthread_mutex here as well?)
>>
>> Sure.
>>
>> May I install the patch with the change?
> 
> Can you at least add a configure check for pthread.h and maybe disable
> locking when not found or erroring out?  I figure we have GCC_AC_THREAD_HEADER

All right, let's error out then.

> for the gthr.h stuff using $target_thread_file (aka --enable-threads=XYZ),
> but as said that's for the target and I don't see any host uses.  We might also
> add an explicit list of hosts (*-linux*?) where we enable thread support for
> lto-plugin, providing opt-in (so you'd have to wrap the mutex taking or
> if-def it out).
> 
> I think you also need to link lto-plugin with -pthread, no?

Yep.

Please see the updated patch.

> On linux
> it might work omitting that but I'm not sure other libc have serial pthread
> stubs in their libc.  BFD ld definitely doesn't link against pthread so
> dlopening lto-plugin will fail (also not all libc might like
> initializing threads
> from a dlopen _init).

What initializing threads do you mean?

Martin

> 
> Richard.
> 
>> Cheers,
>> Martin
>>
>>>
>>>>    free (lto_file.name);
>>>>
>>>>   cleanup:
>>>> @@ -1415,6 +1423,12 @@ onload (struct ld_plugin_tv *tv)
>>>>    struct ld_plugin_tv *p;
>>>>    enum ld_plugin_status status;
>>>>
>>>> +  if (pthread_mutex_init (&plugin_lock, NULL) != 0)
>>>> +    {
>>>> +      fprintf (stderr, "mutex init failed\n");
>>>> +      abort ();
>>>> +    }
>>>> +
>>>>    p = tv;
>>>>    while (p->tv_tag)
>>>>      {
>>>> --
>>>> 2.36.1
>>>>
>>>>

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From f1e2f84dbfdac5c7aee7036e78841cb33c3bad50 Mon Sep 17 00:00:00 2001
From: Martin Liska <mliska@suse.cz>
Date: Mon, 16 May 2022 14:18:41 +0200
Subject: [PATCH] lto-plugin: make claim_file_handler thread-safe

lto-plugin/ChangeLog:

	* lto-plugin.c (plugin_lock): New lock.
	(claim_file_handler): Use mutex for critical section.
	(onload): Initialize mutex.
---
 lto-plugin/config.h.in  |  3 +++
 lto-plugin/configure    | 17 +++++++++++++++--
 lto-plugin/configure.ac |  7 +++++++
 lto-plugin/lto-plugin.c | 20 ++++++++++++++++++++
 4 files changed, 45 insertions(+), 2 deletions(-)

diff --git a/lto-plugin/config.h.in b/lto-plugin/config.h.in
index ddbde7619d5..029e782f1ee 100644
--- a/lto-plugin/config.h.in
+++ b/lto-plugin/config.h.in
@@ -9,6 +9,9 @@
 /* Define to 1 if you have the <memory.h> header file. */
 #undef HAVE_MEMORY_H
 
+/* Define to 1 if pthread.h is present. */
+#undef HAVE_PTHREAD_H
+
 /* Define to 1 if you have the <stdint.h> header file. */
 #undef HAVE_STDINT_H
 
diff --git a/lto-plugin/configure b/lto-plugin/configure
index b820accfd65..6d452063cfb 100755
--- a/lto-plugin/configure
+++ b/lto-plugin/configure
@@ -5643,6 +5643,9 @@ ac_compiler_gnu=$ac_cv_c_compiler_gnu
 
 
 
+# The plug-in depends on pthreads
+LDFLAGS="-lpthread"
+
 # Check whether -static-libgcc is supported.
 saved_LDFLAGS="$LDFLAGS"
 LDFLAGS="$LDFLAGS -static-libgcc"
@@ -6010,6 +6013,16 @@ else
 fi
 
 
+# Check for thread headers.
+ac_fn_c_check_header_mongrel "$LINENO" "pthread.h" "ac_cv_header_pthread_h" "$ac_includes_default"
+if test "x$ac_cv_header_pthread_h" = xyes; then :
+
+$as_echo "#define HAVE_PTHREAD_H 1" >>confdefs.h
+
+fi
+
+
+
 case `pwd` in
   *\ * | *\	*)
     { $as_echo "$as_me:${as_lineno-$LINENO}: WARNING: Libtool does not cope well with whitespace in \`pwd\`" >&5
@@ -12081,7 +12094,7 @@ else
   lt_dlunknown=0; lt_dlno_uscore=1; lt_dlneed_uscore=2
   lt_status=$lt_dlunknown
   cat > conftest.$ac_ext <<_LT_EOF
-#line 12084 "configure"
+#line 12097 "configure"
 #include "confdefs.h"
 
 #if HAVE_DLFCN_H
@@ -12187,7 +12200,7 @@ else
   lt_dlunknown=0; lt_dlno_uscore=1; lt_dlneed_uscore=2
   lt_status=$lt_dlunknown
   cat > conftest.$ac_ext <<_LT_EOF
-#line 12190 "configure"
+#line 12203 "configure"
 #include "confdefs.h"
 
 #if HAVE_DLFCN_H
diff --git a/lto-plugin/configure.ac b/lto-plugin/configure.ac
index bc5b618a495..aafabd4fa7b 100644
--- a/lto-plugin/configure.ac
+++ b/lto-plugin/configure.ac
@@ -13,6 +13,9 @@ AC_PROG_CC
 AC_SYS_LARGEFILE
 ACX_PROG_CC_WARNING_OPTS([-Wall], [ac_lto_plugin_warn_cflags])
 
+# The plug-in depends on pthreads
+LDFLAGS="-lpthread"
+
 # Check whether -static-libgcc is supported.
 saved_LDFLAGS="$LDFLAGS"
 LDFLAGS="$LDFLAGS -static-libgcc"
@@ -87,6 +90,10 @@ AM_CONDITIONAL(LTO_PLUGIN_USE_SYMVER, [test "x$lto_plugin_use_symver" != xno])
 AM_CONDITIONAL(LTO_PLUGIN_USE_SYMVER_GNU, [test "x$lto_plugin_use_symver" = xgnu])
 AM_CONDITIONAL(LTO_PLUGIN_USE_SYMVER_SUN, [test "x$lto_plugin_use_symver" = xsun])
 
+# Check for thread headers.
+AC_CHECK_HEADER(pthread.h,
+  [AC_DEFINE(HAVE_PTHREAD_H, 1, [Define to 1 if pthread.h is present.])])
+
 AM_PROG_LIBTOOL
 ACX_LT_HOST_FLAGS
 AC_SUBST(target_noncanonical)
diff --git a/lto-plugin/lto-plugin.c b/lto-plugin/lto-plugin.c
index 00b760636dc..635e126946b 100644
--- a/lto-plugin/lto-plugin.c
+++ b/lto-plugin/lto-plugin.c
@@ -40,7 +40,11 @@ along with this program; see the file COPYING3.  If not see
 
 #ifdef HAVE_CONFIG_H
 #include "config.h"
+#if !HAVE_PTHREAD_H
+#error POSIX threads are mandatory dependency
 #endif
+#endif
+
 #if HAVE_STDINT_H
 #include <stdint.h>
 #endif
@@ -55,6 +59,7 @@ along with this program; see the file COPYING3.  If not see
 #include <unistd.h>
 #include <fcntl.h>
 #include <sys/types.h>
+#include <pthread.h>
 #ifdef HAVE_SYS_WAIT_H
 #include <sys/wait.h>
 #endif
@@ -157,6 +162,9 @@ enum symbol_style
   ss_uscore,	/* Underscore prefix all symbols.  */
 };
 
+/* Plug-in mutex.  */
+static pthread_mutex_t plugin_lock;
+
 static char *arguments_file_name;
 static ld_plugin_register_claim_file register_claim_file;
 static ld_plugin_register_all_symbols_read register_all_symbols_read;
@@ -1262,15 +1270,18 @@ claim_file_handler (const struct ld_plugin_input_file *file, int *claimed)
 			      lto_file.symtab.syms);
       check (status == LDPS_OK, LDPL_FATAL, "could not add symbols");
 
+      pthread_mutex_lock (&plugin_lock);
       num_claimed_files++;
       claimed_files =
 	xrealloc (claimed_files,
 		  num_claimed_files * sizeof (struct plugin_file_info));
       claimed_files[num_claimed_files - 1] = lto_file;
+      pthread_mutex_unlock (&plugin_lock);
 
       *claimed = 1;
     }
 
+  pthread_mutex_lock (&plugin_lock);
   if (offload_files == NULL)
     {
       /* Add dummy item to the start of the list.  */
@@ -1333,11 +1344,14 @@ claim_file_handler (const struct ld_plugin_input_file *file, int *claimed)
 	offload_files_last_lto = ofld;
       num_offload_files++;
     }
+  pthread_mutex_unlock (&plugin_lock);
 
   goto cleanup;
 
  err:
+  pthread_mutex_lock (&plugin_lock);
   non_claimed_files++;
+  pthread_mutex_unlock (&plugin_lock);
   free (lto_file.name);
 
  cleanup:
@@ -1415,6 +1429,12 @@ onload (struct ld_plugin_tv *tv)
   struct ld_plugin_tv *p;
   enum ld_plugin_status status;
 
+  if (pthread_mutex_init (&plugin_lock, NULL) != 0)
+    {
+      fprintf (stderr, "mutex init failed\n");
+      abort ();
+    }
+
   p = tv;
   while (p->tv_tag)
     {
-- 
2.36.1