[13/16] libdw: Make libdw_findcu thread-safe

Message ID 20231010134300.53830-13-mark@klomp.org
State Changes Requested
Headers
Series [01/16] lib: Add new once_define and once macros to eu-config.h |

Commit Message

Mark Wielaard Oct. 10, 2023, 1:42 p.m. UTC
  From: Heather McIntyre <hsm2@rice.edu>

	* libdw/libdw_findcu.c (findcu_cb): Use eu_tsearch.
	(__libdw_findcu): Use eu_tfind and next_tucu_offset_lock.
	(__libdw_findcu_addr): Use eu_tfind.
	(__libdw_find_split_dbg_addr): Likewise.

Signed-off-by: Heather S. McIntyre <hsm2@rice.edu>
Signed-off-by: Mark Wielaard <mark@klomp.org>
---
 libdw/libdw_findcu.c | 54 ++++++++++++++++++++++++++++----------------
 1 file changed, 35 insertions(+), 19 deletions(-)
  

Comments

Mark Wielaard Oct. 12, 2023, 10:02 p.m. UTC | #1
Hi Heather,

On Tue, Oct 10, 2023 at 03:42:57PM +0200, Mark Wielaard wrote:
> From: Heather McIntyre <hsm2@rice.edu>
> 
> 	* libdw/libdw_findcu.c (findcu_cb): Use eu_tsearch.
> 	(__libdw_findcu): Use eu_tfind and next_tucu_offset_lock.
> 	(__libdw_findcu_addr): Use eu_tfind.
> 	(__libdw_find_split_dbg_addr): Likewise.
> 
> Signed-off-by: Heather S. McIntyre <hsm2@rice.edu>
> Signed-off-by: Mark Wielaard <mark@klomp.org>
> ---
>  libdw/libdw_findcu.c | 54 ++++++++++++++++++++++++++++----------------
>  1 file changed, 35 insertions(+), 19 deletions(-)
> 
> diff --git a/libdw/libdw_findcu.c b/libdw/libdw_findcu.c
> index ed744231..e546fb0f 100644
> --- a/libdw/libdw_findcu.c
> +++ b/libdw/libdw_findcu.c
> @@ -32,9 +32,13 @@
>  #endif
>  
>  #include <assert.h>
> -#include <search.h>
> +#include <eu-search.h>
>  #include "libdwP.h"
>  
> +/* __libdw_findcu modifies "&dbg->next_tu_offset : &dbg->next_cu_offset".
> +   May read or write, so mutual exclusion is enforced to prevent a race. */
> +rwlock_define(static, next_tucu_offset_lock);
> +

Could this be a per struct Dwarf lock?

>  static int
>  findcu_cb (const void *arg1, const void *arg2)
>  {
> @@ -213,7 +217,7 @@ __libdw_intern_next_unit (Dwarf *dbg, bool debug_types)
>
>      Dwarf_Sig8_Hash_insert (&dbg->sig8_hash, unit_id8, newp);
>  
>    /* Add the new entry to the search tree.  */
> -  if (tsearch (newp, tree, findcu_cb) == NULL)
> +  if (eu_tsearch (newp, tree, findcu_cb) == NULL)
>      {
>        /* Something went wrong.  Undo the operation.  */
>        *offsetp = oldoff;

This is OK since when __libdw_intern_next_unit is called from
__libdw_findcu the next_tucu_offset_lock is held.

But there is also a call to __libdw_intern_next_unit from
dwarf_formref_die. So there should also be a lock there?

> @@ -234,28 +238,40 @@ __libdw_findcu (Dwarf *dbg, Dwarf_Off start, bool v4_debug_types)
>  
>    /* Maybe we already know that CU.  */
>    struct Dwarf_CU fake = { .start = start, .end = 0 };
> -  struct Dwarf_CU **found = tfind (&fake, tree, findcu_cb);
> +  struct Dwarf_CU **found = eu_tfind (&fake, tree, findcu_cb);
> +  struct Dwarf_CU *result = NULL;
> +
>    if (found != NULL)
>      return *found;
>  
> -  if (start < *next_offset)
> -    {
> -      __libdw_seterrno (DWARF_E_INVALID_DWARF);
> -      return NULL;
> -    }
> +  rwlock_wrlock(next_tucu_offset_lock);
>  
> -  /* No.  Then read more CUs.  */
> -  while (1)
> +  if (start < *next_offset)
> +    __libdw_seterrno (DWARF_E_INVALID_DWARF);
> +  else
>      {
> -      struct Dwarf_CU *newp = __libdw_intern_next_unit (dbg, v4_debug_types);
> -      if (newp == NULL)
> -	return NULL;
> +      /* No.  Then read more CUs.  */
> +      while (1)
> +	{
> +	  struct Dwarf_CU *newp = __libdw_intern_next_unit (dbg,
> +							    v4_debug_types);
> +	  if (newp == NULL)
> +	    {
> +	      result = NULL;
> +	      break;
> +	    }
>  
> -      /* Is this the one we are looking for?  */
> -      if (start < *next_offset || start == newp->start)
> -	return newp;
> +	  /* Is this the one we are looking for?  */
> +	  if (start < *next_offset || start == newp->start)
> +	    {
> +	      result = newp;
> +	      break;
> +	    }
> +	}
>      }
> -  /* NOTREACHED */
> +
> +  rwlock_unlock(next_tucu_offset_lock);
> +  return result;
>  }

This look OK.

>  struct Dwarf_CU *
> @@ -283,7 +299,7 @@ __libdw_findcu_addr (Dwarf *dbg, void *addr)
>      return NULL;
>  
>    struct Dwarf_CU fake = { .start = start, .end = 0 };
> -  struct Dwarf_CU **found = tfind (&fake, tree, findcu_cb);
> +  struct Dwarf_CU **found = eu_tfind (&fake, tree, findcu_cb);
>  
>    if (found != NULL)
>      return *found;
> @@ -298,7 +314,7 @@ __libdw_find_split_dbg_addr (Dwarf *dbg, void *addr)
>    /* XXX Assumes split DWARF only has CUs in main IDX_debug_info.  */
>    Elf_Data fake_data = { .d_buf = addr, .d_size = 0 };
>    Dwarf fake = { .sectiondata[IDX_debug_info] = &fake_data };
> -  Dwarf **found = tfind (&fake, &dbg->split_tree, __libdw_finddbg_cb);
> +  Dwarf **found = eu_tfind (&fake, &dbg->split_tree, __libdw_finddbg_cb);
>  
>    if (found != NULL)
>      return *found;

OK.

Thanks,

Mark
  
Heather McIntyre Oct. 17, 2023, 8:10 p.m. UTC | #2
Hi Mark,

For the call to __libdw_intern_next_unit in __libdw_findcu, I have updated
the locking to the per struct drawf lock. Although I have not encountered a
data race report regarding the call to __libdw_intern_next_unit in
dwarf_formref_die, I have also placed the updated locking there as well.

On Thu, Oct 12, 2023 at 5:03 PM Mark Wielaard <mark@klomp.org> wrote:

> Hi Heather,
>
> On Tue, Oct 10, 2023 at 03:42:57PM +0200, Mark Wielaard wrote:
> > From: Heather McIntyre <hsm2@rice.edu>
> >
> >       * libdw/libdw_findcu.c (findcu_cb): Use eu_tsearch.
> >       (__libdw_findcu): Use eu_tfind and next_tucu_offset_lock.
> >       (__libdw_findcu_addr): Use eu_tfind.
> >       (__libdw_find_split_dbg_addr): Likewise.
> >
> > Signed-off-by: Heather S. McIntyre <hsm2@rice.edu>
> > Signed-off-by: Mark Wielaard <mark@klomp.org>
> > ---
> >  libdw/libdw_findcu.c | 54 ++++++++++++++++++++++++++++----------------
> >  1 file changed, 35 insertions(+), 19 deletions(-)
> >
> > diff --git a/libdw/libdw_findcu.c b/libdw/libdw_findcu.c
> > index ed744231..e546fb0f 100644
> > --- a/libdw/libdw_findcu.c
> > +++ b/libdw/libdw_findcu.c
> > @@ -32,9 +32,13 @@
> >  #endif
> >
> >  #include <assert.h>
> > -#include <search.h>
> > +#include <eu-search.h>
> >  #include "libdwP.h"
> >
> > +/* __libdw_findcu modifies "&dbg->next_tu_offset :
> &dbg->next_cu_offset".
> > +   May read or write, so mutual exclusion is enforced to prevent a
> race. */
> > +rwlock_define(static, next_tucu_offset_lock);
> > +
>
> Could this be a per struct Dwarf lock?
>
> >  static int
> >  findcu_cb (const void *arg1, const void *arg2)
> >  {
> > @@ -213,7 +217,7 @@ __libdw_intern_next_unit (Dwarf *dbg, bool
> debug_types)
> >
> >      Dwarf_Sig8_Hash_insert (&dbg->sig8_hash, unit_id8, newp);
> >
> >    /* Add the new entry to the search tree.  */
> > -  if (tsearch (newp, tree, findcu_cb) == NULL)
> > +  if (eu_tsearch (newp, tree, findcu_cb) == NULL)
> >      {
> >        /* Something went wrong.  Undo the operation.  */
> >        *offsetp = oldoff;
>
> This is OK since when __libdw_intern_next_unit is called from
> __libdw_findcu the next_tucu_offset_lock is held.
>
> But there is also a call to __libdw_intern_next_unit from
> dwarf_formref_die. So there should also be a lock there?
>
> > @@ -234,28 +238,40 @@ __libdw_findcu (Dwarf *dbg, Dwarf_Off start, bool
> v4_debug_types)
> >
> >    /* Maybe we already know that CU.  */
> >    struct Dwarf_CU fake = { .start = start, .end = 0 };
> > -  struct Dwarf_CU **found = tfind (&fake, tree, findcu_cb);
> > +  struct Dwarf_CU **found = eu_tfind (&fake, tree, findcu_cb);
> > +  struct Dwarf_CU *result = NULL;
> > +
> >    if (found != NULL)
> >      return *found;
> >
> > -  if (start < *next_offset)
> > -    {
> > -      __libdw_seterrno (DWARF_E_INVALID_DWARF);
> > -      return NULL;
> > -    }
> > +  rwlock_wrlock(next_tucu_offset_lock);
> >
> > -  /* No.  Then read more CUs.  */
> > -  while (1)
> > +  if (start < *next_offset)
> > +    __libdw_seterrno (DWARF_E_INVALID_DWARF);
> > +  else
> >      {
> > -      struct Dwarf_CU *newp = __libdw_intern_next_unit (dbg,
> v4_debug_types);
> > -      if (newp == NULL)
> > -     return NULL;
> > +      /* No.  Then read more CUs.  */
> > +      while (1)
> > +     {
> > +       struct Dwarf_CU *newp = __libdw_intern_next_unit (dbg,
> > +
>  v4_debug_types);
> > +       if (newp == NULL)
> > +         {
> > +           result = NULL;
> > +           break;
> > +         }
> >
> > -      /* Is this the one we are looking for?  */
> > -      if (start < *next_offset || start == newp->start)
> > -     return newp;
> > +       /* Is this the one we are looking for?  */
> > +       if (start < *next_offset || start == newp->start)
> > +         {
> > +           result = newp;
> > +           break;
> > +         }
> > +     }
> >      }
> > -  /* NOTREACHED */
> > +
> > +  rwlock_unlock(next_tucu_offset_lock);
> > +  return result;
> >  }
>
> This look OK.
>
> >  struct Dwarf_CU *
> > @@ -283,7 +299,7 @@ __libdw_findcu_addr (Dwarf *dbg, void *addr)
> >      return NULL;
> >
> >    struct Dwarf_CU fake = { .start = start, .end = 0 };
> > -  struct Dwarf_CU **found = tfind (&fake, tree, findcu_cb);
> > +  struct Dwarf_CU **found = eu_tfind (&fake, tree, findcu_cb);
> >
> >    if (found != NULL)
> >      return *found;
> > @@ -298,7 +314,7 @@ __libdw_find_split_dbg_addr (Dwarf *dbg, void *addr)
> >    /* XXX Assumes split DWARF only has CUs in main IDX_debug_info.  */
> >    Elf_Data fake_data = { .d_buf = addr, .d_size = 0 };
> >    Dwarf fake = { .sectiondata[IDX_debug_info] = &fake_data };
> > -  Dwarf **found = tfind (&fake, &dbg->split_tree, __libdw_finddbg_cb);
> > +  Dwarf **found = eu_tfind (&fake, &dbg->split_tree,
> __libdw_finddbg_cb);
> >
> >    if (found != NULL)
> >      return *found;
>
> OK.
>
> Thanks,
>
> Mark
>
  

Patch

diff --git a/libdw/libdw_findcu.c b/libdw/libdw_findcu.c
index ed744231..e546fb0f 100644
--- a/libdw/libdw_findcu.c
+++ b/libdw/libdw_findcu.c
@@ -32,9 +32,13 @@ 
 #endif
 
 #include <assert.h>
-#include <search.h>
+#include <eu-search.h>
 #include "libdwP.h"
 
+/* __libdw_findcu modifies "&dbg->next_tu_offset : &dbg->next_cu_offset".
+   May read or write, so mutual exclusion is enforced to prevent a race. */
+rwlock_define(static, next_tucu_offset_lock);
+
 static int
 findcu_cb (const void *arg1, const void *arg2)
 {
@@ -213,7 +217,7 @@  __libdw_intern_next_unit (Dwarf *dbg, bool debug_types)
     Dwarf_Sig8_Hash_insert (&dbg->sig8_hash, unit_id8, newp);
 
   /* Add the new entry to the search tree.  */
-  if (tsearch (newp, tree, findcu_cb) == NULL)
+  if (eu_tsearch (newp, tree, findcu_cb) == NULL)
     {
       /* Something went wrong.  Undo the operation.  */
       *offsetp = oldoff;
@@ -234,28 +238,40 @@  __libdw_findcu (Dwarf *dbg, Dwarf_Off start, bool v4_debug_types)
 
   /* Maybe we already know that CU.  */
   struct Dwarf_CU fake = { .start = start, .end = 0 };
-  struct Dwarf_CU **found = tfind (&fake, tree, findcu_cb);
+  struct Dwarf_CU **found = eu_tfind (&fake, tree, findcu_cb);
+  struct Dwarf_CU *result = NULL;
+
   if (found != NULL)
     return *found;
 
-  if (start < *next_offset)
-    {
-      __libdw_seterrno (DWARF_E_INVALID_DWARF);
-      return NULL;
-    }
+  rwlock_wrlock(next_tucu_offset_lock);
 
-  /* No.  Then read more CUs.  */
-  while (1)
+  if (start < *next_offset)
+    __libdw_seterrno (DWARF_E_INVALID_DWARF);
+  else
     {
-      struct Dwarf_CU *newp = __libdw_intern_next_unit (dbg, v4_debug_types);
-      if (newp == NULL)
-	return NULL;
+      /* No.  Then read more CUs.  */
+      while (1)
+	{
+	  struct Dwarf_CU *newp = __libdw_intern_next_unit (dbg,
+							    v4_debug_types);
+	  if (newp == NULL)
+	    {
+	      result = NULL;
+	      break;
+	    }
 
-      /* Is this the one we are looking for?  */
-      if (start < *next_offset || start == newp->start)
-	return newp;
+	  /* Is this the one we are looking for?  */
+	  if (start < *next_offset || start == newp->start)
+	    {
+	      result = newp;
+	      break;
+	    }
+	}
     }
-  /* NOTREACHED */
+
+  rwlock_unlock(next_tucu_offset_lock);
+  return result;
 }
 
 struct Dwarf_CU *
@@ -283,7 +299,7 @@  __libdw_findcu_addr (Dwarf *dbg, void *addr)
     return NULL;
 
   struct Dwarf_CU fake = { .start = start, .end = 0 };
-  struct Dwarf_CU **found = tfind (&fake, tree, findcu_cb);
+  struct Dwarf_CU **found = eu_tfind (&fake, tree, findcu_cb);
 
   if (found != NULL)
     return *found;
@@ -298,7 +314,7 @@  __libdw_find_split_dbg_addr (Dwarf *dbg, void *addr)
   /* XXX Assumes split DWARF only has CUs in main IDX_debug_info.  */
   Elf_Data fake_data = { .d_buf = addr, .d_size = 0 };
   Dwarf fake = { .sectiondata[IDX_debug_info] = &fake_data };
-  Dwarf **found = tfind (&fake, &dbg->split_tree, __libdw_finddbg_cb);
+  Dwarf **found = eu_tfind (&fake, &dbg->split_tree, __libdw_finddbg_cb);
 
   if (found != NULL)
     return *found;