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cam: Run all XPT_ASYNC ccbs in a dedicated thread

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Queue all XPT_ASYNC ccb's and run those in a new cam async thread. This thread
is allowed to sleep for things like memory. This should allow us to make all the
registration routines for cam periph drivers simpler since they can assume they
can always allocate memory. This is a separate thread so that any I/O that's
completed in xpt_done_td isn't held up.

This should fix the panics for WAITOK alloations that are elsewhere in the
storage stack that aren't so easy to convert to NOWAIT. Additional future work
will convert other allocations in the registration path to WAITOK should
detailed analysis show it to be safe.

Reviewed by: chs@, rpokala@
Differential Revision:	https://reviews.freebsd.org/D29210
This commit is contained in:
Warner Losh 2021-03-12 13:20:52 -07:00
parent 5fe0cd6503
commit 7381bbee29
2 changed files with 51 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
sys/cam/cam.h
View File

@ -96,6 +96,7 @@ typedef struct {
#define CAM_UNQUEUED_INDEX -1
#define CAM_ACTIVE_INDEX -2
#define CAM_DONEQ_INDEX -3
#define CAM_ASYNC_INDEX -4
#define CAM_EXTRAQ_INDEX INT_MAX
} cam_pinfo;

49
sys/cam/cam_xpt.c
View File

@ -180,6 +180,7 @@ struct cam_doneq {
static struct cam_doneq cam_doneqs[MAXCPU];
static u_int __read_mostly cam_num_doneqs;
static struct proc *cam_proc;
static struct cam_doneq cam_async;
SYSCTL_INT(_kern_cam, OID_AUTO, num_doneqs, CTLFLAG_RDTUN,
&cam_num_doneqs, 0, "Number of completion queues/threads");
@ -271,6 +272,7 @@ static void xptpoll(struct cam_sim *sim);
static void camisr_runqueue(void);
static void xpt_done_process(struct ccb_hdr *ccb_h);
static void xpt_done_td(void *);
static void xpt_async_td(void *);
static dev_match_ret xptbusmatch(struct dev_match_pattern *patterns,
u_int num_patterns, struct cam_eb *bus);
static dev_match_ret xptdevicematch(struct dev_match_pattern *patterns,
@ -972,6 +974,15 @@ xpt_init(void *dummy)
return (ENOMEM);
}
mtx_init(&cam_async.cam_doneq_mtx, "CAM async", NULL, MTX_DEF);
STAILQ_INIT(&cam_async.cam_doneq);
if (kproc_kthread_add(xpt_async_td, &cam_async,
&cam_proc, NULL, 0, 0, "cam", "async") != 0) {
printf("xpt_init: Cannot init async thread "
"- failing attach\n");
return (ENOMEM);
}
/*
* Register a callback for when interrupts are enabled.
*/
@ -3146,8 +3157,16 @@ xpt_action_default(union ccb *start_ccb)
xpt_done(start_ccb);
break;
case XPT_ASYNC:
/*
* Queue the async operation so it can be run from a sleepable
* context.
*/
start_ccb->ccb_h.status = CAM_REQ_CMP;
xpt_done(start_ccb);
mtx_lock(&cam_async.cam_doneq_mtx);
STAILQ_INSERT_TAIL(&cam_async.cam_doneq, &start_ccb->ccb_h, sim_links.stqe);
start_ccb->ccb_h.pinfo.index = CAM_ASYNC_INDEX;
mtx_unlock(&cam_async.cam_doneq_mtx);
wakeup(&cam_async.cam_doneq);
break;
default:
case XPT_SDEV_TYPE:
@ -5472,6 +5491,34 @@ xpt_done_process(struct ccb_hdr *ccb_h)
mtx_unlock(mtx);
}
/*
* Parameterize instead and use xpt_done_td?
*/
static void
xpt_async_td(void *arg)
{
struct cam_doneq *queue = arg;
struct ccb_hdr *ccb_h;
STAILQ_HEAD(, ccb_hdr) doneq;
STAILQ_INIT(&doneq);
mtx_lock(&queue->cam_doneq_mtx);
while (1) {
while (STAILQ_EMPTY(&queue->cam_doneq))
msleep(&queue->cam_doneq, &queue->cam_doneq_mtx,
PRIBIO, "-", 0);
STAILQ_CONCAT(&doneq, &queue->cam_doneq);
mtx_unlock(&queue->cam_doneq_mtx);
while ((ccb_h = STAILQ_FIRST(&doneq)) != NULL) {
STAILQ_REMOVE_HEAD(&doneq, sim_links.stqe);
xpt_done_process(ccb_h);
}
mtx_lock(&queue->cam_doneq_mtx);
}
}
void
xpt_done_td(void *arg)
{