Messages in this thread Patch in this message | | | Date | Wed, 12 Mar 2008 13:09:21 +0100 | From | Peter Zijlstra <> | Subject | [PATCH 1/2] lockdep: fix recursive read lock validation |
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__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 <a.p.zijlstra@chello.nl> CC: Gautham R Shenoy <ego@in.ibm.com> --- 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); --
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