we have seen a few crashes that look like:
[250696.381575] RIP: 0010:[<ffffffffa0a1f9e4>] [<ffffffffa0a1f9e4>]
mdc_exit_request+0x74/0xb0 [mdc]
...
[250696.381575] Call Trace:
[250696.381575] [<ffffffffa0a25042>]
mdc_intent_getattr_async_interpret+0x82/0x500 [mdc]
[250696.381575] [<ffffffffa089efd0>] ptlrpc_check_set+0x200/0x1690 [ptlrpc]
[250696.381575] [<ffffffffa08d3140>] ptlrpcd_check+0x110/0x250 [ptlrpc]
and i sort of gather the problem arises from mdc_enter_request().
it allocates an mdc_cache_waiter on the stack and inserts it into the
wait list and then returns.
int mdc_enter_request(struct client_obd *cli)
...
struct mdc_cache_waiter mcw;
...
list_add_tail(&mcw.mcw_entry, &cli->cl_cache_waiters);
init_waitqueue_head(&mcw.mcw_waitq);
later mdc_exit_request() finds this mcw by iterating the list.
seeing as mcw was allocated on the stack, i dont think you can do this.
mcw might have been reused by the time mdc_exit_request() gets around
to removing it.
void mdc_exit_request(struct client_obd *cli)
...
mcw = list_entry(l, struct mdc_cache_waiter, mcw_entry);
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