[13/16] libdw: Make libdw_findcu thread-safe
Commit Message
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
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
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
>
@@ -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;