__lock_acquire( .read = 2 )
hlock->read = read; /* [1] */
validate_chain()
ret = check_deadlock(); /* returns 2 when recursive */
if (ret == 2)
hlock->read = 2; /* but it was already 2 from [1] */
check_prevs_add()
if (hlock->read != 2)
/* add to dependency chain */
So it will never add a recursive read lock to the dependency chain. Fix this
by setting hlock->read to 1 when its the first recursive lock instance.
This means that the following sequence is now invalid, whereas previously
it was considered valid:
rlock(a); rlock(b); runlock(b); runlock(a)
rlock(b); rlock(a);
It really is invalid when considered against write locks.
Signed-off-by: Peter Zijlstra <[email protected]>
CC: Gautham R Shenoy <[email protected]>
---
kernel/lockdep.c | 9 ++++-----
lib/locking-selftest.c | 12 ++++++------
2 files changed, 10 insertions(+), 11 deletions(-)
Index: linux-2.6-2/kernel/lockdep.c
===================================================================
--- linux-2.6-2.orig/kernel/lockdep.c
+++ linux-2.6-2/kernel/lockdep.c
@@ -1557,12 +1557,11 @@ static int validate_chain(struct task_st
if (!ret)
return 0;
/*
- * Mark recursive read, as we jump over it when
- * building dependencies (just like we jump over
- * trylock entries):
+ * If we are the first recursive read, don't jump over our
+ * dependency.
*/
- if (ret == 2)
- hlock->read = 2;
+ if (hlock->read == 2 && ret != 2)
+ hlock->read = 1;
/*
* Add dependency only if this lock is not the head
* of the chain, and if it's not a secondary read-lock:
Index: linux-2.6-2/lib/locking-selftest.c
===================================================================
--- linux-2.6-2.orig/lib/locking-selftest.c
+++ linux-2.6-2/lib/locking-selftest.c
@@ -1135,12 +1135,12 @@ void locking_selftest(void)
debug_locks_silent = !debug_locks_verbose;
DO_TESTCASE_6R("A-A deadlock", AA);
- DO_TESTCASE_6R("A-B-B-A deadlock", ABBA);
- DO_TESTCASE_6R("A-B-B-C-C-A deadlock", ABBCCA);
- DO_TESTCASE_6R("A-B-C-A-B-C deadlock", ABCABC);
- DO_TESTCASE_6R("A-B-B-C-C-D-D-A deadlock", ABBCCDDA);
- DO_TESTCASE_6R("A-B-C-D-B-D-D-A deadlock", ABCDBDDA);
- DO_TESTCASE_6R("A-B-C-D-B-C-D-A deadlock", ABCDBCDA);
+ DO_TESTCASE_6("A-B-B-A deadlock", ABBA);
+ DO_TESTCASE_6("A-B-B-C-C-A deadlock", ABBCCA);
+ DO_TESTCASE_6("A-B-C-A-B-C deadlock", ABCABC);
+ DO_TESTCASE_6("A-B-B-C-C-D-D-A deadlock", ABBCCDDA);
+ DO_TESTCASE_6("A-B-C-D-B-D-D-A deadlock", ABCDBDDA);
+ DO_TESTCASE_6("A-B-C-D-B-C-D-A deadlock", ABCDBCDA);
DO_TESTCASE_6("double unlock", double_unlock);
DO_TESTCASE_6("initialize held", init_held);
DO_TESTCASE_6_SUCCESS("bad unlock order", bad_unlock_order);
--
On Wed, Mar 12, 2008 at 01:09:21PM +0100, Peter Zijlstra wrote:
> __lock_acquire( .read = 2 )
> hlock->read = read; /* [1] */
> validate_chain()
> ret = check_deadlock(); /* returns 2 when recursive */
>
> if (ret == 2)
> hlock->read = 2; /* but it was already 2 from [1] */
>
> check_prevs_add()
> if (hlock->read != 2)
> /* add to dependency chain */
>
> So it will never add a recursive read lock to the dependency chain. Fix this
> by setting hlock->read to 1 when its the first recursive lock instance.
>
> This means that the following sequence is now invalid, whereas previously
> it was considered valid:
>
> rlock(a); rlock(b); runlock(b); runlock(a)
> rlock(b); rlock(a);
>
> It really is invalid when considered against write locks.
>
> Signed-off-by: Peter Zijlstra <[email protected]>
> CC: Gautham R Shenoy <[email protected]>
Tested-by: Gautham R Shenoy <[email protected]>
> ---
> kernel/lockdep.c | 9 ++++-----
> lib/locking-selftest.c | 12 ++++++------
> 2 files changed, 10 insertions(+), 11 deletions(-)
>
> Index: linux-2.6-2/kernel/lockdep.c
> ===================================================================
> --- linux-2.6-2.orig/kernel/lockdep.c
> +++ linux-2.6-2/kernel/lockdep.c
> @@ -1557,12 +1557,11 @@ static int validate_chain(struct task_st
> if (!ret)
> return 0;
> /*
> - * Mark recursive read, as we jump over it when
> - * building dependencies (just like we jump over
> - * trylock entries):
> + * If we are the first recursive read, don't jump over our
> + * dependency.
> */
> - if (ret == 2)
> - hlock->read = 2;
> + if (hlock->read == 2 && ret != 2)
> + hlock->read = 1;
> /*
> * Add dependency only if this lock is not the head
> * of the chain, and if it's not a secondary read-lock:
> Index: linux-2.6-2/lib/locking-selftest.c
> ===================================================================
> --- linux-2.6-2.orig/lib/locking-selftest.c
> +++ linux-2.6-2/lib/locking-selftest.c
> @@ -1135,12 +1135,12 @@ void locking_selftest(void)
> debug_locks_silent = !debug_locks_verbose;
>
> DO_TESTCASE_6R("A-A deadlock", AA);
> - DO_TESTCASE_6R("A-B-B-A deadlock", ABBA);
> - DO_TESTCASE_6R("A-B-B-C-C-A deadlock", ABBCCA);
> - DO_TESTCASE_6R("A-B-C-A-B-C deadlock", ABCABC);
> - DO_TESTCASE_6R("A-B-B-C-C-D-D-A deadlock", ABBCCDDA);
> - DO_TESTCASE_6R("A-B-C-D-B-D-D-A deadlock", ABCDBDDA);
> - DO_TESTCASE_6R("A-B-C-D-B-C-D-A deadlock", ABCDBCDA);
> + DO_TESTCASE_6("A-B-B-A deadlock", ABBA);
> + DO_TESTCASE_6("A-B-B-C-C-A deadlock", ABBCCA);
> + DO_TESTCASE_6("A-B-C-A-B-C deadlock", ABCABC);
> + DO_TESTCASE_6("A-B-B-C-C-D-D-A deadlock", ABBCCDDA);
> + DO_TESTCASE_6("A-B-C-D-B-D-D-A deadlock", ABCDBDDA);
> + DO_TESTCASE_6("A-B-C-D-B-C-D-A deadlock", ABCDBCDA);
> DO_TESTCASE_6("double unlock", double_unlock);
> DO_TESTCASE_6("initialize held", init_held);
> DO_TESTCASE_6_SUCCESS("bad unlock order", bad_unlock_order);
>
> --
--
Thanks and Regards
gautham