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, 172 insertions, 0 deletions

diff --git a/arch/alpha/boot/misc.c b/arch/alpha/boot/misc.c
new file mode 100644
index 000000000..1ab91852d
--- /dev/null
+++ b/arch/alpha/boot/misc.c
@@ -0,0 +1,172 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * misc.c
+ * 
+ * This is a collection of several routines from gzip-1.0.3 
+ * adapted for Linux.
+ *
+ * malloc by Hannu Savolainen 1993 and Matthias Urlichs 1994
+ *
+ * Modified for ARM Linux by Russell King
+ *
+ * Nicolas Pitre <nico@visuaide.com>  1999/04/14 :
+ *  For this code to run directly from Flash, all constant variables must
+ *  be marked with 'const' and all other variables initialized at run-time 
+ *  only.  This way all non constant variables will end up in the bss segment,
+ *  which should point to addresses in RAM and cleared to 0 on start.
+ *  This allows for a much quicker boot time.
+ *
+ * Modified for Alpha, from the ARM version, by Jay Estabrook 2003.
+ */
+
+#include <linux/kernel.h>
+#include <linux/slab.h>
+
+#include <linux/uaccess.h>
+
+#define memzero(s,n)	memset ((s),0,(n))
+#define puts		srm_printk
+extern long srm_printk(const char *, ...)
+     __attribute__ ((format (printf, 1, 2)));
+
+/*
+ * gzip declarations
+ */
+#define OF(args)  args
+#define STATIC static
+
+typedef unsigned char  uch;
+typedef unsigned short ush;
+typedef unsigned long  ulg;
+
+#define WSIZE 0x8000		/* Window size must be at least 32k, */
+				/* and a power of two */
+
+static uch *inbuf;		/* input buffer */
+static uch *window;		/* Sliding window buffer */
+
+static unsigned insize;		/* valid bytes in inbuf */
+static unsigned inptr;		/* index of next byte to be processed in inbuf */
+static unsigned outcnt;		/* bytes in output buffer */
+
+/* gzip flag byte */
+#define ASCII_FLAG   0x01 /* bit 0 set: file probably ascii text */
+#define CONTINUATION 0x02 /* bit 1 set: continuation of multi-part gzip file */
+#define EXTRA_FIELD  0x04 /* bit 2 set: extra field present */
+#define ORIG_NAME    0x08 /* bit 3 set: original file name present */
+#define COMMENT      0x10 /* bit 4 set: file comment present */
+#define ENCRYPTED    0x20 /* bit 5 set: file is encrypted */
+#define RESERVED     0xC0 /* bit 6,7:   reserved */
+
+#define get_byte()  (inptr < insize ? inbuf[inptr++] : fill_inbuf())
+
+/* Diagnostic functions */
+#ifdef DEBUG
+#  define Assert(cond,msg) {if(!(cond)) error(msg);}
+#  define Trace(x) fprintf x
+#  define Tracev(x) {if (verbose) fprintf x ;}
+#  define Tracevv(x) {if (verbose>1) fprintf x ;}
+#  define Tracec(c,x) {if (verbose && (c)) fprintf x ;}
+#  define Tracecv(c,x) {if (verbose>1 && (c)) fprintf x ;}
+#else
+#  define Assert(cond,msg)
+#  define Trace(x)
+#  define Tracev(x)
+#  define Tracevv(x)
+#  define Tracec(c,x)
+#  define Tracecv(c,x)
+#endif
+
+static int  fill_inbuf(void);
+static void flush_window(void);
+static void error(char *m);
+
+static char *input_data;
+static int  input_data_size;
+
+static uch *output_data;
+static ulg output_ptr;
+static ulg bytes_out;
+
+static void error(char *m);
+
+extern int end;
+static ulg free_mem_ptr;
+static ulg free_mem_end_ptr;
+
+#define HEAP_SIZE 0x3000
+
+#include "../../../lib/inflate.c"
+
+/* ===========================================================================
+ * Fill the input buffer. This is called only when the buffer is empty
+ * and at least one byte is really needed.
+ */
+int fill_inbuf(void)
+{
+	if (insize != 0)
+		error("ran out of input data");
+
+	inbuf = input_data;
+	insize = input_data_size;
+
+	inptr = 1;
+	return inbuf[0];
+}
+
+/* ===========================================================================
+ * Write the output window window[0..outcnt-1] and update crc and bytes_out.
+ * (Used for the decompressed data only.)
+ */
+void flush_window(void)
+{
+	ulg c = crc;
+	unsigned n;
+	uch *in, *out, ch;
+
+	in = window;
+	out = &output_data[output_ptr];
+	for (n = 0; n < outcnt; n++) {
+		ch = *out++ = *in++;
+		c = crc_32_tab[((int)c ^ ch) & 0xff] ^ (c >> 8);
+	}
+	crc = c;
+	bytes_out += (ulg)outcnt;
+	output_ptr += (ulg)outcnt;
+	outcnt = 0;
+/*	puts("."); */
+}
+
+static void error(char *x)
+{
+	puts("\n\n");
+	puts(x);
+	puts("\n\n -- System halted");
+
+	while(1);	/* Halt */
+}
+
+unsigned int
+decompress_kernel(void *output_start,
+		  void *input_start,
+		  size_t ksize,
+		  size_t kzsize)
+{
+	output_data		= (uch *)output_start;
+	input_data		= (uch *)input_start;
+	input_data_size		= kzsize; /* use compressed size */
+
+	/* FIXME FIXME FIXME */
+	free_mem_ptr		= (ulg)output_start + ksize;
+	free_mem_end_ptr	= (ulg)output_start + ksize + 0x200000;
+	/* FIXME FIXME FIXME */
+
+	/* put in temp area to reduce initial footprint */
+	window = malloc(WSIZE);
+
+	makecrc();
+/*	puts("Uncompressing Linux..."); */
+	gunzip();
+/*	puts(" done, booting the kernel.\n"); */
+	return output_ptr;
+}