[mpich-commits] [mpich] MPICH primary repository branch, master, updated. v3.1.2-152-g0eeed17
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http://git.mpich.org/mpich.git/commitdiff/0eeed17df88f41285e43c61a4f6863c0c0b85fb3
commit 0eeed17df88f41285e43c61a4f6863c0c0b85fb3
Author: Huiwei Lu <huiweilu at mcs.anl.gov>
Date: Tue Jul 15 17:34:26 2014 -0500
Fixes deadlock in multi-threaded MPI_Comm_idup
This patch implements the "eager" protocol used in MPI_Comm_idup.
Without this patch, test/mpi/threads/comm/comm_idup will crash due to
segmentation fault caused by livelock.
It uses the same algorithm as multi-threaded
MPIR_Get_contextid_sparse_group to avoid deadlock in multi-threaded
context_id allocation, but in a nonblocking way. The nonblocking
mechanism is explained in the comment of function
sched_get_cid_nonblock.
Fixes #2069
Signed-off-by: Pavan Balaji <balaji at anl.gov>
diff --git a/src/mpi/comm/commutil.c b/src/mpi/comm/commutil.c
index 8713a2f..60db478 100644
--- a/src/mpi/comm/commutil.c
+++ b/src/mpi/comm/commutil.c
@@ -833,7 +833,17 @@ fn_fail:
}
-/* In multi-threaded case, mask_in_used is used to maintain thread safety. In
+/* EAGER CONTEXT ID ALLOCATION: Attempt to allocate the context ID during the
+ * initial synchronization step. If eager protocol fails, threads fall back to
+ * the base algorithm.
+ *
+ * They are used to avoid deadlock in multi-threaded case. In single-threaded
+ * case, they are not used.
+ */
+static volatile int eager_nelem = -1;
+static volatile int eager_in_use = 0;
+
+/* In multi-threaded case, mask_in_use is used to maintain thread safety. In
* single-threaded case, it is always 0. */
static volatile int mask_in_use = 0;
@@ -938,13 +948,6 @@ fn_fail:
#else /* MPICH_IS_THREADED is set and true */
-/* EAGER CONTEXT ID ALLOCATION: Attempt to allocate the context ID during the
- * initial synchronization step. If eager protocol fails, threads fall back to
- * the base algorithm.
- */
-static volatile int eager_nelem = -1;
-static volatile int eager_in_use = 0;
-
#undef FUNCNAME
#define FUNCNAME MPIR_Get_contextid_sparse
#undef FCNAME
@@ -1230,6 +1233,8 @@ struct gcn_state {
MPIR_Context_id_t *ctx0;
MPIR_Context_id_t *ctx1;
int own_mask;
+ int own_eager_mask;
+ int first_iter;
MPID_Comm *comm_ptr;
MPID_Comm *comm_ptr_inter;
MPID_Sched_t s;
@@ -1283,21 +1288,48 @@ static int sched_cb_gcn_allocate_cid(MPID_Comm *comm, int tag, void *state)
MPIR_Context_id_t newctxid;
MPIU_THREAD_CS_ENTER(CONTEXTID,);
- if (st->own_mask) {
+ if (st->own_eager_mask) {
+ newctxid = MPIR_Find_and_allocate_context_id(st->local_mask);
+ if (st->ctx0)
+ *st->ctx0 = newctxid;
+ if (st->ctx1)
+ *st->ctx1 = newctxid;
+
+ st->own_eager_mask = 0;
+ eager_in_use = 0;
+
+ if (newctxid <= 0) {
+ /* else we did not find a context id. Give up the mask in case
+ * there is another thread (with a lower input context id)
+ * waiting for it. We need to ensure that any other threads
+ * have the opportunity to run, hence yielding */
+ MPIU_THREAD_CS_YIELD(CONTEXTID,);
+ }
+ } else if (st->own_mask) {
newctxid = MPIR_Find_and_allocate_context_id(st->local_mask);
if (st->ctx0)
*st->ctx0 = newctxid;
if (st->ctx1)
*st->ctx1 = newctxid;
+
+ /* reset flags for the next try */
mask_in_use = 0;
if (newctxid > 0) {
if (lowestContextId == st->comm_ptr->context_id)
lowestContextId = MPIR_MAXID;
+ } else {
+ /* else we did not find a context id. Give up the mask in case
+ * there is another thread (with a lower input context id)
+ * waiting for it. We need to ensure that any other threads
+ * have the opportunity to run, hence yielding */
+ MPIU_THREAD_CS_YIELD(CONTEXTID,);
}
+ } else {
+ /* As above, force this thread to yield */
+ MPIU_THREAD_CS_YIELD(CONTEXTID,);
}
- MPIU_THREAD_CS_EXIT(CONTEXTID,);
if (*st->ctx0 == 0) {
/* do not own mask, try again */
@@ -1311,6 +1343,8 @@ static int sched_cb_gcn_allocate_cid(MPID_Comm *comm, int tag, void *state)
MPID_SCHED_BARRIER(st->s);
}
+ MPIU_THREAD_CS_EXIT(CONTEXTID,);
+
/* --BEGIN ERROR HANDLING-- */
/* --END ERROR HANDLING-- */
fn_fail:
@@ -1327,18 +1361,40 @@ static int sched_cb_gcn_copy_mask(MPID_Comm *comm, int tag, void *state)
struct gcn_state *st = state;
MPIU_THREAD_CS_ENTER(CONTEXTID,);
- if (st->comm_ptr->context_id < lowestContextId) {
- lowestContextId = st->comm_ptr->context_id;
- }
- if (mask_in_use || (st->comm_ptr->context_id != lowestContextId)) {
+ if (st->first_iter) {
memset(st->local_mask, 0, MPIR_MAX_CONTEXT_MASK * sizeof(int));
- st->own_mask = 0;
+ st->own_eager_mask = 0;
+
+ /* Attempt to reserve the eager mask segment */
+ if (!eager_in_use && eager_nelem > 0) {
+ int i;
+ for (i = 0; i < eager_nelem; i++)
+ st->local_mask[i] = context_mask[i];
+
+ eager_in_use = 1;
+ st->own_eager_mask = 1;
+ }
+ st->first_iter = 0;
} else {
- MPIU_Memcpy(st->local_mask, context_mask, MPIR_MAX_CONTEXT_MASK * sizeof(uint32_t));
- mask_in_use = 1;
- st->own_mask = 1;
+ if (st->comm_ptr->context_id < lowestContextId) {
+ lowestContextId = st->comm_ptr->context_id;
+ }
+ if (mask_in_use || (st->comm_ptr->context_id != lowestContextId)) {
+ memset(st->local_mask, 0, MPIR_MAX_CONTEXT_MASK * sizeof(int));
+ st->own_mask = 0;
+ } else {
+ /* Copy safe mask segment to local_mask */
+ int i;
+ for (i = 0; i < eager_nelem; i++)
+ st->local_mask[i] = 0;
+ for (i = eager_nelem; i < MPIR_MAX_CONTEXT_MASK; i++)
+ st->local_mask[i] = context_mask[i];
+
+ mask_in_use = 1;
+ st->own_mask = 1;
+ }
}
- MPIU_THREAD_CS_ENTER(CONTEXTID,);
+ MPIU_THREAD_CS_EXIT(CONTEXTID,);
mpi_errno = st->comm_ptr->coll_fns->Iallreduce_sched(MPI_IN_PLACE, st->local_mask, MPIR_MAX_CONTEXT_MASK,
MPI_UINT32_T, MPI_BAND, st->comm_ptr, st->s);
@@ -1354,28 +1410,41 @@ fn_fail:
}
-/** The multi-threaded nonblocking algorithm of getting a context id
+/** Allocating a new context ID collectively over the given communicator in a
+ * nonblocking way.
+ *
+ * The nonblocking mechanism is implemented by inserting MPIDU_Sched_entry to
+ * the nonblocking collective progress, which is a part of the progress engine.
+ * It uses a two-level linked list 'all_schedules' to manager all nonblocking
+ * collective calls: the first level is a linked list of struct MPIDU_Sched;
+ * and each struct MPIDU_Sched is an array of struct MPIDU_Sched_entry. The
+ * following four functions are used together to implement the algorithm:
+ * sched_cb_gcn_copy_mask, sched_cb_gcn_allocate_cid, sched_cb_gcn_bcast and
+ * sched_get_cid_nonblock.
*
- * 1. It shares the same global flag 'mask_in_use' with other communicator
- * functions to protect access to context_mask. And use CONTEXTID lock to
- * protext critical sections.
+ * The above four functions use the same algorithm as
+ * MPIR_Get_contextid_sparse_group (multi-threaded version) to allocate a
+ * context id. The algorithm needs to retry the allocation process in the case
+ * of conflicts. In MPIR_Get_contextid_sparse_group, it is a while loop. In
+ * the nonblocking algorithm, 1) new entries are inserted to the end of
+ * schedule to replace the 'while' loop in MPI_Comm_dup algorithm; 2) all
+ * arguments passed to sched_get_cid_nonblock are saved to gcn_state in order
+ * to be called in the future; 3) in sched_cb_gcn_allocate_cid, if the first
+ * try failed, it will insert sched_cb_gcn_copy_mask to the schedule again.
*
- * 2. It uses the same algorithm as multithreaded MPI_Comm_dup (multi-threaded
- * vertion of MPIR_Get_contextid_sparse_group) to allocate a context id, but in
- * a nonblocking way. In the case of conflicts, the algorithm needs to retry
- * the allocation process again. In the nonblocking algorithm, 1) new entries
- * are inserted to the end of schedule to replace the 'while' loop in
- * MPI_Comm_dup algorithm; 2) all arguments passed to sched_get_cid_nonblock
- * are saved to gcn_state in order to be called in the future; 3) in
- * sched_cb_gcn_allocate_cid, if the first try failed, it will insert
- * sched_cb_gcn_copy_mask to the schedule again.
+ * To ensure thread-safety, it shares the same global flag 'mask_in_use' with
+ * other communicator functions to protect access to context_mask. And use
+ * CONTEXTID lock to protect critical sections.
*
- * 3. There is a subtle difference between INTRACOMM and INTERCOMM when
+ * There is a subtle difference between INTRACOMM and INTERCOMM when
* duplicating a communicator. They needed to be treated differently in
* current algorithm. Specifically, 1) when calling sched_get_cid_nonblock, the
* parameters are different; 2) updating newcommp->recvcontext_id in
* MPIR_Get_intercomm_contextid_nonblock has been moved to sched_cb_gcn_bcast
* because this should happen after sched_cb_gcn_allocate_cid has succeed.
+ *
+ * To avoid deadlock or livelock, it uses the same eager protocol as
+ * multi-threaded MPIR_Get_contextid_sparse_group.
*/
#undef FUNCNAME
#define FUNCNAME sched_get_cid_nonblock
@@ -1406,6 +1475,14 @@ static int sched_get_cid_nonblock(MPID_Comm *comm_ptr, MPIR_Context_id_t *ctx0,
st->s = s;
st->gcn_cid_kind = gcn_cid_kind;
*(st->ctx0) = 0;
+ st->own_eager_mask = 0;
+ st->first_iter = 1;
+ if (eager_nelem < 0) {
+ /* Ensure that at least one word of deadlock-free context IDs is
+ always set aside for the base protocol */
+ MPIU_Assert( MPIR_CVAR_CTXID_EAGER_SIZE >= 0 && MPIR_CVAR_CTXID_EAGER_SIZE < MPIR_MAX_CONTEXT_MASK-1 );
+ eager_nelem = MPIR_CVAR_CTXID_EAGER_SIZE;
+ }
MPIU_THREAD_CS_EXIT(CONTEXTID,);
mpi_errno = MPID_Sched_cb(&sched_cb_gcn_copy_mask, st, s);
diff --git a/test/mpi/threads/comm/testlist b/test/mpi/threads/comm/testlist
index 6d94573..2dfc780 100644
--- a/test/mpi/threads/comm/testlist
+++ b/test/mpi/threads/comm/testlist
@@ -3,5 +3,5 @@ dup_leak_test 2
comm_dup_deadlock 4
comm_create_threads 4
comm_create_group_threads 4
-comm_idup 4 mpiversion=3.0 xfail=ticket2069
+comm_idup 4 mpiversion=3.0
ctxidup 4
-----------------------------------------------------------------------
Summary of changes:
src/mpi/comm/commutil.c | 143 ++++++++++++++++++++++++++++++---------
test/mpi/threads/comm/testlist | 2 +-
2 files changed, 111 insertions(+), 34 deletions(-)
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