sched_ext: Maintain an online cid mask in the scheduler arenagrafted

Schedulers on the default cid mapping treat [0, nr_online_cids) as the
online set and restart on hotplug. Schedulers that install their own mapping
with scx_bpf_cid_override() have no way to learn which cids are online: the
count no longer identifies members and the CPU-form cpumask is unusable from
cid programs. This is an obvious hole in the cid API.

Add scx_bpf_online_cmask(), a kernel-maintained cmask in the scheduler's
arena, allocated alongside the per-CPU scratch masks and populated after the
cid mapping is finalized and before ops.init(), for child schedulers too.
The pointer stays valid through ops.exit() with no reference to take. It is
the arena offset as a void pointer, the same form struct_ops arena arguments
arrive in. The verifier types the void return as a scalar for the program's
arena cast.

The mask follows the SCX hotplug notifications: seeded from cpu_active_mask
and updated before ops.cid_online/offline() runs, so it lags cpu_online_mask
only inside a hotplug transition. Updates walk the scheduler list under the
lock that also serializes unlinking. Reads are live, not atomic snapshots.
Root initialization excludes hotplug.

v2: Reworded the getter kerneldoc (Andrea Righi).

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>

1 files changed, 208 insertions, 0 deletions

diff --git a/fs/afs/misc.c b/fs/afs/misc.c
new file mode 100644
index 000000000..c8a7f2660
--- /dev/null
+++ b/fs/afs/misc.c
@@ -0,0 +1,208 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/* miscellaneous bits
+ *
+ * Copyright (C) 2002, 2007 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/errno.h>
+#include <crypto/krb5.h>
+#include "internal.h"
+#include "afs_fs.h"
+#include "protocol_uae.h"
+
+/*
+ * convert an AFS abort code to a Linux error number
+ */
+int afs_abort_to_error(u32 abort_code)
+{
+	switch (abort_code) {
+		/* Low errno codes inserted into abort namespace */
+	case 13:		return -EACCES;
+	case 27:		return -EFBIG;
+	case 30:		return -EROFS;
+
+		/* VICE "special error" codes; 101 - 111 */
+	case VSALVAGE:		return -EIO;
+	case VNOVNODE:		return -ENOENT;
+	case VNOVOL:		return -ENOMEDIUM;
+	case VVOLEXISTS:	return -EEXIST;
+	case VNOSERVICE:	return -EIO;
+	case VOFFLINE:		return -ENOENT;
+	case VONLINE:		return -EEXIST;
+	case VDISKFULL:		return -ENOSPC;
+	case VOVERQUOTA:	return -EDQUOT;
+	case VBUSY:		return -EBUSY;
+	case VMOVED:		return -ENXIO;
+
+		/* Volume Location server errors */
+	case AFSVL_IDEXIST:		return -EEXIST;
+	case AFSVL_IO:			return -EREMOTEIO;
+	case AFSVL_NAMEEXIST:		return -EEXIST;
+	case AFSVL_CREATEFAIL:		return -EREMOTEIO;
+	case AFSVL_NOENT:		return -ENOMEDIUM;
+	case AFSVL_EMPTY:		return -ENOMEDIUM;
+	case AFSVL_ENTDELETED:		return -ENOMEDIUM;
+	case AFSVL_BADNAME:		return -EINVAL;
+	case AFSVL_BADINDEX:		return -EINVAL;
+	case AFSVL_BADVOLTYPE:		return -EINVAL;
+	case AFSVL_BADSERVER:		return -EINVAL;
+	case AFSVL_BADPARTITION:	return -EINVAL;
+	case AFSVL_REPSFULL:		return -EFBIG;
+	case AFSVL_NOREPSERVER:		return -ENOENT;
+	case AFSVL_DUPREPSERVER:	return -EEXIST;
+	case AFSVL_RWNOTFOUND:		return -ENOENT;
+	case AFSVL_BADREFCOUNT:		return -EINVAL;
+	case AFSVL_SIZEEXCEEDED:	return -EINVAL;
+	case AFSVL_BADENTRY:		return -EINVAL;
+	case AFSVL_BADVOLIDBUMP:	return -EINVAL;
+	case AFSVL_IDALREADYHASHED:	return -EINVAL;
+	case AFSVL_ENTRYLOCKED:		return -EBUSY;
+	case AFSVL_BADVOLOPER:		return -EBADRQC;
+	case AFSVL_BADRELLOCKTYPE:	return -EINVAL;
+	case AFSVL_RERELEASE:		return -EREMOTEIO;
+	case AFSVL_BADSERVERFLAG:	return -EINVAL;
+	case AFSVL_PERM:		return -EACCES;
+	case AFSVL_NOMEM:		return -EREMOTEIO;
+
+		/* Unified AFS error table */
+	case UAEPERM:			return -EPERM;
+	case UAENOENT:			return -ENOENT;
+	case UAEAGAIN:			return -EAGAIN;
+	case UAEACCES:			return -EACCES;
+	case UAEBUSY:			return -EBUSY;
+	case UAEEXIST:			return -EEXIST;
+	case UAENOTDIR:			return -ENOTDIR;
+	case UAEISDIR:			return -EISDIR;
+	case UAEFBIG:			return -EFBIG;
+	case UAENOSPC:			return -ENOSPC;
+	case UAEROFS:			return -EROFS;
+	case UAEMLINK:			return -EMLINK;
+	case UAEDEADLK:			return -EDEADLK;
+	case UAENAMETOOLONG:		return -ENAMETOOLONG;
+	case UAENOLCK:			return -ENOLCK;
+	case UAENOTEMPTY:		return -ENOTEMPTY;
+	case UAELOOP:			return -ELOOP;
+	case UAEOVERFLOW:		return -EOVERFLOW;
+	case UAENOMEDIUM:		return -ENOMEDIUM;
+	case UAEDQUOT:			return -EDQUOT;
+
+		/* RXKAD abort codes; from include/rxrpc/packet.h.  ET "RXK" == 0x1260B00 */
+	case RXKADINCONSISTENCY: return -EPROTO;
+	case RXKADPACKETSHORT:	return -EPROTO;
+	case RXKADLEVELFAIL:	return -EKEYREJECTED;
+	case RXKADTICKETLEN:	return -EKEYREJECTED;
+	case RXKADOUTOFSEQUENCE: return -EPROTO;
+	case RXKADNOAUTH:	return -EKEYREJECTED;
+	case RXKADBADKEY:	return -EKEYREJECTED;
+	case RXKADBADTICKET:	return -EKEYREJECTED;
+	case RXKADUNKNOWNKEY:	return -EKEYREJECTED;
+	case RXKADEXPIRED:	return -EKEYEXPIRED;
+	case RXKADSEALEDINCON:	return -EKEYREJECTED;
+	case RXKADDATALEN:	return -EKEYREJECTED;
+	case RXKADILLEGALLEVEL:	return -EKEYREJECTED;
+
+	case RXGK_INCONSISTENCY:	return -EPROTO;
+	case RXGK_PACKETSHORT:		return -EPROTO;
+	case RXGK_BADCHALLENGE:		return -EPROTO;
+	case RXGK_SEALEDINCON:		return -EKEYREJECTED;
+	case RXGK_NOTAUTH:		return -EKEYREJECTED;
+	case RXGK_EXPIRED:		return -EKEYEXPIRED;
+	case RXGK_BADLEVEL:		return -EKEYREJECTED;
+	case RXGK_BADKEYNO:		return -EKEYREJECTED;
+	case RXGK_NOTRXGK:		return -EKEYREJECTED;
+	case RXGK_UNSUPPORTED:		return -EKEYREJECTED;
+	case RXGK_GSSERROR:		return -EKEYREJECTED;
+#ifdef RXGK_BADETYPE
+	case RXGK_BADETYPE:		return -ENOPKG;
+#endif
+#ifdef RXGK_BADTOKEN
+	case RXGK_BADTOKEN:		return -EKEYREJECTED;
+#endif
+#ifdef RXGK_BADETYPE
+	case RXGK_DATALEN:		return -EPROTO;
+#endif
+#ifdef RXGK_BADQOP
+	case RXGK_BADQOP:		return -EKEYREJECTED;
+#endif
+
+	case KRB5_PROG_KEYTYPE_NOSUPP:	return -ENOPKG;
+
+	case RXGEN_OPCODE:	return -ENOTSUPP;
+	case RX_INVALID_OPERATION:	return -ENOTSUPP;
+
+	default:		return -EREMOTEIO;
+	}
+}
+
+/*
+ * Select the error to report from a set of errors.
+ */
+void afs_prioritise_error(struct afs_error *e, int error, u32 abort_code)
+{
+	switch (error) {
+	case 0:
+		e->aborted = false;
+		e->error = 0;
+		return;
+	default:
+		if (e->error == -ETIMEDOUT ||
+		    e->error == -ETIME)
+			return;
+		fallthrough;
+	case -ETIMEDOUT:
+	case -ETIME:
+		if (e->error == -ENOMEM ||
+		    e->error == -ENONET)
+			return;
+		fallthrough;
+	case -ENOMEM:
+	case -ENONET:
+		if (e->error == -ERFKILL)
+			return;
+		fallthrough;
+	case -ERFKILL:
+		if (e->error == -EADDRNOTAVAIL)
+			return;
+		fallthrough;
+	case -EADDRNOTAVAIL:
+		if (e->error == -ENETUNREACH)
+			return;
+		fallthrough;
+	case -ENETUNREACH:
+		if (e->error == -EHOSTUNREACH)
+			return;
+		fallthrough;
+	case -EHOSTUNREACH:
+		if (e->error == -EHOSTDOWN)
+			return;
+		fallthrough;
+	case -EHOSTDOWN:
+		if (e->error == -ECONNREFUSED)
+			return;
+		fallthrough;
+	case -ECONNREFUSED:
+		if (e->error == -ECONNRESET)
+			return;
+		fallthrough;
+	case -ECONNRESET: /* Responded, but call expired. */
+		if (e->responded)
+			return;
+		e->error = error;
+		e->aborted = false;
+		return;
+
+	case -ECONNABORTED:
+		e->error = afs_abort_to_error(abort_code);
+		e->aborted = true;
+		e->responded = true;
+		return;
+	case -ENETRESET: /* Responded, but we seem to have changed address */
+		e->aborted = false;
+		e->responded = true;
+		e->error = error;
+		return;
+	}
+}