"panic: malloc(M_WAITOK) in non-sleepable context" after r364296 -> r364341

[Mark Johnston]

On Tue, Aug 18, 2020 at 03:24:52PM +0200, Mateusz Guzik wrote:
> Try this:
> 
> diff --git a/sys/kern/kern_malloc.c b/sys/kern/kern_malloc.c
> index 46eb1c4347c..7b94ca7b880 100644
> --- a/sys/kern/kern_malloc.c
> +++ b/sys/kern/kern_malloc.c
> @@ -618,8 +618,8 @@ void *
>         unsigned long osize = size;
>  #endif
> 
> -       KASSERT((flags & M_WAITOK) == 0 || THREAD_CAN_SLEEP(),
> -           ("malloc(M_WAITOK) in non-sleepable context"));
> +       if ((flags & M_WAITOK) != 0)
> +               WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, NULL, __func__);
> 
>  #ifdef MALLOC_DEBUG
>         va = NULL;
> diff --git a/sys/vm/uma_core.c b/sys/vm/uma_core.c
> index 37d78354200..2e1267ec02f 100644
> --- a/sys/vm/uma_core.c
> +++ b/sys/vm/uma_core.c
> @@ -3355,8 +3355,8 @@ uma_zalloc_arg(uma_zone_t zone, void *udata, int flags)
>         uma_cache_bucket_t bucket;
>         uma_cache_t cache;
> 
> -       KASSERT((flags & M_WAITOK) == 0 || THREAD_CAN_SLEEP(),
> -           ("uma_zalloc(M_WAITOK) in non-sleepable context"));
> +       if ((flags & M_WAITOK) != 0)
> +               WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, NULL, __func__);
> 
>         /* Enable entropy collection for RANDOM_ENABLE_UMA kernel option */
>         random_harvest_fast_uma(&zone, sizeof(zone), RANDOM_UMA);

Doesn't it only print a warning if non-sleepable locks are held?
THREAD_CAN_SLEEP() catches other cases, like epoch sections and worker
threads that are not allowed to sleep (CAM doneq threads in this case).
Otherwise uma_zalloc_debug() already checks with WITNESS.

I'm inclined to simply revert the commit for now.  Alternately,
disk_alloc() could be modified to handle M_NOWAIT/M_WAITOK flags, and
that could be used in daregister() and other CAM periph drivers.
daregister() already uses M_NOWAIT to allocate the driver softc itself.

diff --git a/sys/cam/scsi/scsi_da.c b/sys/cam/scsi/scsi_da.c
index d648d511b1a2..d940e7db24e0 100644
--- a/sys/cam/scsi/scsi_da.c
+++ b/sys/cam/scsi/scsi_da.c
@@ -2767,18 +2767,23 @@ daregister(struct cam_periph *periph, void *arg)
 		return(CAM_REQ_CMP_ERR);
 	}
 
-	softc = (struct da_softc *)malloc(sizeof(*softc), M_DEVBUF,
-	    M_NOWAIT|M_ZERO);
-
+	softc = malloc(sizeof(*softc), M_DEVBUF, M_NOWAIT | M_ZERO);
 	if (softc == NULL) {
 		printf("daregister: Unable to probe new device. "
 		       "Unable to allocate softc\n");
 		return(CAM_REQ_CMP_ERR);
 	}
+	softc->disk = disk_alloc_flags(M_NOWAIT);
+	if (softc->disk == NULL) {
+		printf("daregister: Unable to probe new device. "
+		       "Unable to allocate disk structure\n");
+		return (CAM_REQ_CMP_ERR);
+	}
 
 	if (cam_iosched_init(&softc->cam_iosched, periph) != 0) {
 		printf("daregister: Unable to probe new device. "
 		       "Unable to allocate iosched memory\n");
+		disk_destroy(softc->disk);
 		free(softc, M_DEVBUF);
 		return(CAM_REQ_CMP_ERR);
 	}
@@ -2898,7 +2903,6 @@ daregister(struct cam_periph *periph, void *arg)
 	/*
 	 * Register this media as a disk.
 	 */
-	softc->disk = disk_alloc();
 	softc->disk->d_devstat = devstat_new_entry(periph->periph_name,
 			  periph->unit_number, 0,
 			  DEVSTAT_BS_UNAVAILABLE,
diff --git a/sys/geom/geom_disk.c b/sys/geom/geom_disk.c
index eaba770828d0..c07494ab4ec0 100644
--- a/sys/geom/geom_disk.c
+++ b/sys/geom/geom_disk.c
@@ -850,15 +850,22 @@ g_disk_ident_adjust(char *ident, size_t size)
 }
 
 struct disk *
-disk_alloc(void)
+disk_alloc_flags(int mflag)
 {
 	struct disk *dp;
 
-	dp = g_malloc(sizeof(struct disk), M_WAITOK | M_ZERO);
-	LIST_INIT(&dp->d_aliases);
+	dp = g_malloc(sizeof(struct disk), mflag | M_ZERO);
+	if (dp != NULL)
+		LIST_INIT(&dp->d_aliases);
 	return (dp);
 }
 
+struct disk *
+disk_alloc(void)
+{
+	return (disk_alloc_flags(M_WAITOK));
+}
+
 void
 disk_create(struct disk *dp, int version)
 {
diff --git a/sys/geom/geom_disk.h b/sys/geom/geom_disk.h
index 8e2282a09a3a..794ce2cc38bd 100644
--- a/sys/geom/geom_disk.h
+++ b/sys/geom/geom_disk.h
@@ -137,6 +137,7 @@ struct disk {
 #define	DISKFLAG_WRITE_PROTECT		0x0100
 
 struct disk *disk_alloc(void);
+struct disk *disk_alloc_flags(int mflag);
 void disk_create(struct disk *disk, int version);
 void disk_destroy(struct disk *disk);
 void disk_gone(struct disk *disk);