When we destroy a cm_id, we must purge associated events from the
event queue. If the cm_id is for a listen request, we also purge
corresponding pending connect requests. This requires destroying
the cm_id's associated with the connect requests by calling
rdma_destroy_id(). rdma_destroy_id() blocks until all outstanding
callbacks have completed.
The issue is that we hold file->mut while purging events from the
event queue. We also acquire file->mut in our event handler.
Calling rdma_destroy_id() while holding file->mut can lead to a
deadlock, since the event handler callback cannot acquire file->mut,
which prevents rdma_destroy_id() from completing.
Fix this by moving events to purge from the event queue to a
temporary list. We can then release file->mut and call
rdma_destroy_id() outside of holding any locks.
Bug report by Or Gerlitz <ogerl...@mellanox.com>:
[ INFO: possible circular locking dependency detected ]
3.3.0-rc5-00008-g79f1e43-dirty #34 Tainted: G I
tgtd/9018 is trying to acquire lock:
(&id_priv->handler_mutex){+.+.+.}, at: [<ffffffffa0359a41>]
rdma_destroy_id+0x33/0x1f0 [rdma_cm]
but task is already holding lock:
(&file->mut){+.+.+.}, at: [<ffffffffa02470fe>] ucma_free_ctx+0xb6/0x196
[rdma_ucm]
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #1 (&file->mut){+.+.+.}:
[<ffffffff810682f3>] lock_acquire+0xf0/0x116
[<ffffffff8135f179>] mutex_lock_nested+0x64/0x2e6
[<ffffffffa0247636>] ucma_event_handler+0x148/0x1dc [rdma_ucm]
[<ffffffffa035a79a>] cma_ib_handler+0x1a7/0x1f7 [rdma_cm]
[<ffffffffa0333e88>] cm_process_work+0x32/0x119 [ib_cm]
[<ffffffffa03362ab>] cm_work_handler+0xfb8/0xfe5 [ib_cm]
[<ffffffff810423e2>] process_one_work+0x2bd/0x4a6
[<ffffffff810429e2>] worker_thread+0x1d6/0x350
[<ffffffff810462a6>] kthread+0x84/0x8c
[<ffffffff81369624>] kernel_thread_helper+0x4/0x10
-> #0 (&id_priv->handler_mutex){+.+.+.}:
[<ffffffff81067b86>] __lock_acquire+0x10d5/0x1752
[<ffffffff810682f3>] lock_acquire+0xf0/0x116
[<ffffffff8135f179>] mutex_lock_nested+0x64/0x2e6
[<ffffffffa0359a41>] rdma_destroy_id+0x33/0x1f0 [rdma_cm]
[<ffffffffa024715f>] ucma_free_ctx+0x117/0x196 [rdma_ucm]
[<ffffffffa0247255>] ucma_close+0x77/0xb4 [rdma_ucm]
[<ffffffff810df6ef>] fput+0x117/0x1cf
[<ffffffff810dc76e>] filp_close+0x6d/0x78
[<ffffffff8102b667>] put_files_struct+0xbd/0x17d
[<ffffffff8102b76d>] exit_files+0x46/0x4e
[<ffffffff8102d057>] do_exit+0x299/0x75d
[<ffffffff8102d599>] do_group_exit+0x7e/0xa9
[<ffffffff8103ae4b>] get_signal_to_deliver+0x536/0x555
[<ffffffff81001717>] do_signal+0x39/0x634
[<ffffffff81001d39>] do_notify_resume+0x27/0x69
[<ffffffff81361c03>] retint_signal+0x46/0x83
other info that might help us debug this:
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
lock(&file->mut);
lock(&id_priv->handler_mutex);
lock(&file->mut);
lock(&id_priv->handler_mutex);
*** DEADLOCK ***
1 lock held by tgtd/9018:
#0: (&file->mut){+.+.+.}, at: [<ffffffffa02470fe>] ucma_free_ctx+0xb6/0x196
[rdma_ucm]
stack backtrace:
Pid: 9018, comm: tgtd Tainted: G I 3.3.0-rc5-00008-g79f1e43-dirty #34
Call Trace:
[<ffffffff81029e9c>] ? console_unlock+0x18e/0x207
[<ffffffff81066433>] print_circular_bug+0x28e/0x29f
[<ffffffff81067b86>] __lock_acquire+0x10d5/0x1752
[<ffffffff810682f3>] lock_acquire+0xf0/0x116
[<ffffffffa0359a41>] ? rdma_destroy_id+0x33/0x1f0 [rdma_cm]
[<ffffffff8135f179>] mutex_lock_nested+0x64/0x2e6
[<ffffffffa0359a41>] ? rdma_destroy_id+0x33/0x1f0 [rdma_cm]
[<ffffffff8106546d>] ? trace_hardirqs_on_caller+0x11e/0x155
[<ffffffff810654b1>] ? trace_hardirqs_on+0xd/0xf
[<ffffffffa0359a41>] rdma_destroy_id+0x33/0x1f0 [rdma_cm]
[<ffffffffa024715f>] ucma_free_ctx+0x117/0x196 [rdma_ucm]
[<ffffffffa0247255>] ucma_close+0x77/0xb4 [rdma_ucm]
[<ffffffff810df6ef>] fput+0x117/0x1cf
[<ffffffff810dc76e>] filp_close+0x6d/0x78
[<ffffffff8102b667>] put_files_struct+0xbd/0x17d
[<ffffffff8102b5cc>] ? put_files_struct+0x22/0x17d
[<ffffffff8102b76d>] exit_files+0x46/0x4e
[<ffffffff8102d057>] do_exit+0x299/0x75d
[<ffffffff8102d599>] do_group_exit+0x7e/0xa9
[<ffffffff8103ae4b>] get_signal_to_deliver+0x536/0x555
[<ffffffff810654b1>] ? trace_hardirqs_on+0xd/0xf
[<ffffffff81001717>] do_signal+0x39/0x634
[<ffffffff8135e037>] ? printk+0x3c/0x45
[<ffffffff8106546d>] ? trace_hardirqs_on_caller+0x11e/0x155
[<ffffffff810654b1>] ? trace_hardirqs_on+0xd/0xf
[<ffffffff81361803>] ? _raw_spin_unlock_irq+0x2b/0x40
[<ffffffff81039011>] ? set_current_blocked+0x44/0x49
[<ffffffff81361bce>] ? retint_signal+0x11/0x83
[<ffffffff81001d39>] do_notify_resume+0x27/0x69
[<ffffffff8118a1fe>] ? trace_hardirqs_on_thunk+0x3a/0x3f
[<ffffffff81361c03>] retint_signal+0x46/0x83
Signed-off-by: Sean Hefty <sean.he...@intel.com>
---
This bug has been in the code for quite a while, and this is the first time
that it's been detected. Given the likelihood of hitting it, it's probably
safe to wait for 3.4
drivers/infiniband/core/ucma.c | 37 ++++++++++++++++++-------------------
1 files changed, 18 insertions(+), 19 deletions(-)
diff --git a/drivers/infiniband/core/ucma.c b/drivers/infiniband/core/ucma.c
index 5034a87..5861cdb 100644
--- a/drivers/infiniband/core/ucma.c
+++ b/drivers/infiniband/core/ucma.c
@@ -449,24 +449,6 @@ static void ucma_cleanup_multicast(struct ucma_context
*ctx)
mutex_unlock(&mut);
}
-static void ucma_cleanup_events(struct ucma_context *ctx)
-{
- struct ucma_event *uevent, *tmp;
-
- list_for_each_entry_safe(uevent, tmp, &ctx->file->event_list, list) {
- if (uevent->ctx != ctx)
- continue;
-
- list_del(&uevent->list);
-
- /* clear incoming connections. */
- if (uevent->resp.event == RDMA_CM_EVENT_CONNECT_REQUEST)
- rdma_destroy_id(uevent->cm_id);
-
- kfree(uevent);
- }
-}
-
static void ucma_cleanup_mc_events(struct ucma_multicast *mc)
{
struct ucma_event *uevent, *tmp;
@@ -480,9 +462,16 @@ static void ucma_cleanup_mc_events(struct ucma_multicast
*mc)
}
}
+/*
+ * We cannot hold file->mut when calling rdma_destroy_id() or we can
+ * deadlock. We also acquire file->mut in ucma_event_handler(), and
+ * rdma_destroy_id() will wait until all callbacks have completed.
+ */
static int ucma_free_ctx(struct ucma_context *ctx)
{
int events_reported;
+ struct ucma_event *uevent, *tmp;
+ LIST_HEAD(list);
/* No new events will be generated after destroying the id. */
rdma_destroy_id(ctx->cm_id);
@@ -491,10 +480,20 @@ static int ucma_free_ctx(struct ucma_context *ctx)
/* Cleanup events not yet reported to the user. */
mutex_lock(&ctx->file->mut);
- ucma_cleanup_events(ctx);
+ list_for_each_entry_safe(uevent, tmp, &ctx->file->event_list, list) {
+ if (uevent->ctx == ctx)
+ list_move_tail(&uevent->list, &list);
+ }
list_del(&ctx->list);
mutex_unlock(&ctx->file->mut);
+ list_for_each_entry_safe(uevent, tmp, &list, list) {
+ list_del(&uevent->list);
+ if (uevent->resp.event == RDMA_CM_EVENT_CONNECT_REQUEST)
+ rdma_destroy_id(uevent->cm_id);
+ kfree(uevent);
+ }
+
events_reported = ctx->events_reported;
kfree(ctx);
return events_reported;
--
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