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Don't deadlock in __dl_iterate_phdr while (un)loading objects.
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Andreas Schwab authored and Ulrich Drepper committed May 3, 2010
1 parent c739ec3 commit 5a2a1d7
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Showing 8 changed files with 39 additions and 4 deletions.
13 changes: 13 additions & 0 deletions ChangeLog
Original file line number Diff line number Diff line change
@@ -1,3 +1,16 @@
2010-02-02 Andreas Schwab <schwab@redhat.com>

* sysdeps/generic/ldsodefs.h (struct rtld_global): Add
_dl_load_write_lock.
* elf/rtld.c (_rtld_global): Initialize it.
* elf/dl-support.c (_dl_load_write_lock): Define .
* elf/dl-close.c (_dl_close_worker): Lock GL(dl_load_write_lock)
when modifying the list of loaded objects.
* elf/dl-load.c (lose): Likewise.
* elf/dl-object.c (_dl_new_object): Likewise.
* elf/dl-iteratephdr.c (__dl_iterate_phdr): Lock
GL(dl_load_write_lock) instead of GL(dl_load_lock).

2010-05-03 Ulrich Drepper <drepper@redhat.com>

* elf/dl-iteratephdr.c (__dl_iterate_phdr): Remove unnecessary
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5 changes: 5 additions & 0 deletions elf/dl-close.c
Original file line number Diff line number Diff line change
Expand Up @@ -507,6 +507,9 @@ _dl_close_worker (struct link_map *map)
size_t tls_free_end;
tls_free_start = tls_free_end = NO_TLS_OFFSET;

/* We modify the list of loaded objects. */
__rtld_lock_lock_recursive (GL(dl_load_write_lock));

/* Check each element of the search list to see if all references to
it are gone. */
for (unsigned int i = first_loaded; i < nloaded; ++i)
Expand Down Expand Up @@ -665,6 +668,8 @@ _dl_close_worker (struct link_map *map)
}
}

__rtld_lock_unlock_recursive (GL(dl_load_write_lock));

/* If we removed any object which uses TLS bump the generation counter. */
if (any_tls)
{
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8 changes: 4 additions & 4 deletions elf/dl-iteratephdr.c
Original file line number Diff line number Diff line change
Expand Up @@ -26,7 +26,7 @@
static void
cancel_handler (void *arg __attribute__((unused)))
{
__rtld_lock_unlock_recursive (GL(dl_load_lock));
__rtld_lock_unlock_recursive (GL(dl_load_write_lock));
}

hidden_proto (__dl_iterate_phdr)
Expand All @@ -38,8 +38,8 @@ __dl_iterate_phdr (int (*callback) (struct dl_phdr_info *info,
struct dl_phdr_info info;
int ret = 0;

/* Make sure we are alone. */
__rtld_lock_lock_recursive (GL(dl_load_lock));
/* Make sure nobody modifies the list of loaded objects. */
__rtld_lock_lock_recursive (GL(dl_load_write_lock));
__libc_cleanup_push (cancel_handler, 0);

/* We have to determine the namespace of the caller since this determines
Expand Down Expand Up @@ -79,7 +79,7 @@ __dl_iterate_phdr (int (*callback) (struct dl_phdr_info *info,

/* Release the lock. */
__libc_cleanup_pop (0);
__rtld_lock_unlock_recursive (GL(dl_load_lock));
__rtld_lock_unlock_recursive (GL(dl_load_write_lock));

return ret;
}
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3 changes: 3 additions & 0 deletions elf/dl-load.c
Original file line number Diff line number Diff line change
Expand Up @@ -803,6 +803,8 @@ lose (int code, int fd, const char *name, char *realname, struct link_map *l,
(void) __close (fd);
if (l != NULL)
{
/* We modify the list of loaded objects. */
__rtld_lock_lock_recursive (GL(dl_load_write_lock));
/* Remove the stillborn object from the list and free it. */
assert (l->l_next == NULL);
if (l->l_prev == NULL)
Expand All @@ -813,6 +815,7 @@ lose (int code, int fd, const char *name, char *realname, struct link_map *l,
l->l_prev->l_next = NULL;
--GL(dl_ns)[l->l_ns]._ns_nloaded;
free (l);
__rtld_lock_unlock_recursive (GL(dl_load_write_lock));
}
free (realname);

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5 changes: 5 additions & 0 deletions elf/dl-object.c
Original file line number Diff line number Diff line change
Expand Up @@ -93,6 +93,9 @@ _dl_new_object (char *realname, const char *libname, int type,
new->l_scope = new->l_scope_mem;
new->l_scope_max = sizeof (new->l_scope_mem) / sizeof (new->l_scope_mem[0]);

/* We modify the list of loaded objects. */
__rtld_lock_lock_recursive (GL(dl_load_write_lock));

/* Counter for the scopes we have to handle. */
idx = 0;

Expand All @@ -114,6 +117,8 @@ _dl_new_object (char *realname, const char *libname, int type,
new->l_serial = GL(dl_load_adds);
++GL(dl_load_adds);

__rtld_lock_unlock_recursive (GL(dl_load_write_lock));

/* If we have no loader the new object acts as it. */
if (loader == NULL)
loader = new;
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4 changes: 4 additions & 0 deletions elf/dl-support.c
Original file line number Diff line number Diff line change
Expand Up @@ -166,6 +166,10 @@ const ElfW(Ehdr) *_dl_sysinfo_dso;
the loaded object might as well require a call to this function.
At this time it is not anymore a problem to modify the tables. */
__rtld_lock_define_initialized_recursive (, _dl_load_lock)
/* This lock is used to keep __dl_iterate_phdr from inspecting the
list of loaded objects while an object is added to or removed from
that list. */
__rtld_lock_define_initialized_recursive (, _dl_load_write_lock)


#ifdef HAVE_AUX_VECTOR
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1 change: 1 addition & 0 deletions elf/rtld.c
Original file line number Diff line number Diff line change
Expand Up @@ -126,6 +126,7 @@ struct rtld_global _rtld_global =
._dl_stack_flags = PF_R|PF_W|PF_X,
#ifdef _LIBC_REENTRANT
._dl_load_lock = _RTLD_LOCK_RECURSIVE_INITIALIZER,
._dl_load_write_lock = _RTLD_LOCK_RECURSIVE_INITIALIZER,
#endif
._dl_nns = 1,
._dl_ns =
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4 changes: 4 additions & 0 deletions sysdeps/generic/ldsodefs.h
Original file line number Diff line number Diff line change
Expand Up @@ -416,6 +416,10 @@ struct rtld_global
the loaded object might as well require a call to this function.
At this time it is not anymore a problem to modify the tables. */
__rtld_lock_define_recursive (EXTERN, _dl_load_lock)
/* This lock is used to keep __dl_iterate_phdr from inspecting the
list of loaded objects while an object is added to or removed
from that list. */
__rtld_lock_define_recursive (EXTERN, _dl_load_write_lock)

/* Incremented whenever something may have been added to dl_loaded. */
EXTERN unsigned long long _dl_load_adds;
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