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Re: [PATCH][BZ #16573] Fix for hang when using mtrace with MALLOC_TRACE set


On 8/8/14 3:46 PM, Kwok Cheung Yeung wrote:
A hang can occur if the mtrace output is diverted to a file (by
setting the MALLOC_TRACE environment variable) and an mtrace problem
is found. The mtrace hook leads to a call of __libc_message(), which
eventually results in a call to malloc(), causing another mtrace hook
to be called.  This hook then attempts to reacquire the same lock
that was already claimed by the first hook, resulting in an infinite
hang.

This patch fixes this by making all mtrace hooks temporarily
uninstall all mtrace hooks for the duration of the call, so that
there will not be another call to an mtrace hook further down the
call chain.

I'm cleaning up the queue of old malloc patches.

I'm proposing a similar patch but refactored slightly.

Thank you for waiting almost 5 years :}

2014-08-08  Kwok Cheung Yeung  <kcy@codesourcery.com>

     [BZ #16573]
     * malloc/mtrace.c (tr_freehook): Move function prototype to
     before the hook definitions.  Disable all hooks before calling
     the caller or old hook, and re-enable all hooks afterwards.
     (tr_mallochook): Likewise.
     (tr_reallochook): Likewise.
     (tr_freehook): Likewise.
---
diff --git a/malloc/mtrace.c b/malloc/mtrace.c
index 91e5710..593b212 100644
--- a/malloc/mtrace.c
+++ b/malloc/mtrace.c
@@ -120,6 +120,10 @@ lock_and_info (const __ptr_t caller, Dl_info *mem)
    return res;
  }

+static __ptr_t tr_mallochook (size_t, const __ptr_t);
+static __ptr_t tr_reallochook (__ptr_t, size_t, const __ptr_t);
+static __ptr_t tr_memalignhook (size_t, size_t, const __ptr_t);
+
  static void
  tr_freehook (__ptr_t ptr, const __ptr_t caller)
  {
@@ -138,11 +142,17 @@ tr_freehook (__ptr_t ptr, const __ptr_t caller)
        __libc_lock_lock (lock);
      }
    __free_hook = tr_old_free_hook;
+  __malloc_hook = tr_old_malloc_hook;
+  __realloc_hook = tr_old_realloc_hook;
+  __memalign_hook = tr_old_memalign_hook;
    if (tr_old_free_hook != NULL)
      (*tr_old_free_hook)(ptr, caller);
    else
      free (ptr);
    __free_hook = tr_freehook;
+  __malloc_hook = tr_mallochook;
+  __realloc_hook = tr_reallochook;
+  __memalign_hook = tr_memalignhook;
    __libc_lock_unlock (lock);
  }

@@ -154,12 +164,18 @@ tr_mallochook (size_t size, const __ptr_t caller)
    Dl_info mem;
    Dl_info *info = lock_and_info (caller, &mem);

+  __free_hook = tr_old_free_hook;
    __malloc_hook = tr_old_malloc_hook;
+  __realloc_hook = tr_old_realloc_hook;
+  __memalign_hook = tr_old_memalign_hook;
    if (tr_old_malloc_hook != NULL)
      hdr = (__ptr_t) (*tr_old_malloc_hook)(size, caller);
    else
      hdr = (__ptr_t) malloc (size);
+  __free_hook = tr_freehook;
    __malloc_hook = tr_mallochook;
+  __realloc_hook = tr_reallochook;
+  __memalign_hook = tr_memalignhook;

    tr_where (caller, info);
    /* We could be printing a NULL here; that's OK.  */
@@ -187,6 +203,7 @@ tr_reallochook (__ptr_t ptr, size_t size, const __ptr_t caller)
    __free_hook = tr_old_free_hook;
    __malloc_hook = tr_old_malloc_hook;
    __realloc_hook = tr_old_realloc_hook;
+  __memalign_hook = tr_old_memalign_hook;
    if (tr_old_realloc_hook != NULL)
      hdr = (__ptr_t) (*tr_old_realloc_hook)(ptr, size, caller);
    else
@@ -194,6 +211,7 @@ tr_reallochook (__ptr_t ptr, size_t size, const __ptr_t caller)
    __free_hook = tr_freehook;
    __malloc_hook = tr_mallochook;
    __realloc_hook = tr_reallochook;
+  __memalign_hook = tr_memalignhook;

    tr_where (caller, info);
    if (hdr == NULL)
@@ -229,14 +247,18 @@ tr_memalignhook (size_t alignment, size_t size, const __ptr_t caller)
    Dl_info mem;
    Dl_info *info = lock_and_info (caller, &mem);

-  __memalign_hook = tr_old_memalign_hook;
+  __free_hook = tr_old_free_hook;
    __malloc_hook = tr_old_malloc_hook;
+  __realloc_hook = tr_old_realloc_hook;
+  __memalign_hook = tr_old_memalign_hook;
    if (tr_old_memalign_hook != NULL)
      hdr = (__ptr_t) (*tr_old_memalign_hook)(alignment, size, caller);
    else
      hdr = (__ptr_t) memalign (alignment, size);
-  __memalign_hook = tr_memalignhook;
+  __free_hook = tr_freehook;
    __malloc_hook = tr_mallochook;
+  __realloc_hook = tr_reallochook;
+  __memalign_hook = tr_memalignhook;

    tr_where (caller, info);
    /* We could be printing a NULL here; that's OK.  */


--
Cheers,
Carlos.


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