Merge tag 'printk-for-5.13' of git://git.kernel.org/pub/scm/linux/kernel/git/printk/linux

Pull printk updates from Petr Mladek:

 - Stop synchronizing kernel log buffer readers by logbuf_lock. As a
   result, the access to the buffer is fully lockless now.

   Note that printk() itself still uses locks because it tries to flush
   the messages to the console immediately. Also the per-CPU temporary
   buffers are still there because they prevent infinite recursion and
   serialize backtraces from NMI. All this is going to change in the
   future.

 - kmsg_dump API rework and cleanup as a side effect of the logbuf_lock
   removal.

 - Make bstr_printf() aware that %pf and %pF formats could deference the
   given pointer.

 - Show also page flags by %pGp format.

 - Clarify the documentation for plain pointer printing.

 - Do not show no_hash_pointers warning multiple times.

 - Update Senozhatsky email address.

 - Some clean up.

* tag 'printk-for-5.13' of git://git.kernel.org/pub/scm/linux/kernel/git/printk/linux: (24 commits)
  lib/vsprintf.c: remove leftover 'f' and 'F' cases from bstr_printf()
  printk: clarify the documentation for plain pointer printing
  kernel/printk.c: Fixed mundane typos
  printk: rename vprintk_func to vprintk
  vsprintf: dump full information of page flags in pGp
  mm, slub: don't combine pr_err with INFO
  mm, slub: use pGp to print page flags
  MAINTAINERS: update Senozhatsky email address
  lib/vsprintf: do not show no_hash_pointers message multiple times
  printk: console: remove unnecessary safe buffer usage
  printk: kmsg_dump: remove _nolock() variants
  printk: remove logbuf_lock
  printk: introduce a kmsg_dump iterator
  printk: kmsg_dumper: remove @Active field
  printk: add syslog_lock
  printk: use atomic64_t for devkmsg_user.seq
  printk: use seqcount_latch for clear_seq
  printk: introduce CONSOLE_LOG_MAX
  printk: consolidate kmsg_dump_get_buffer/syslog_print_all code
  printk: refactor kmsg_dump_get_buffer()
  ...

Author: torvalds

Documentation/core-api/printk-formats.rst

@@ -79,7 +79,19 @@ Pointers printed without a specifier extension (i.e unadorned %p) are
 hashed to prevent leaking information about the kernel memory layout. This
 has the added benefit of providing a unique identifier. On 64-bit machines
 the first 32 bits are zeroed. The kernel will print ``(ptrval)`` until it
-gathers enough entropy. If you *really* want the address see %px below.
+gathers enough entropy.
+
+When possible, use specialised modifiers such as %pS or %pB (described below)
+to avoid the need of providing an unhashed address that has to be interpreted
+post-hoc. If not possible, and the aim of printing the address is to provide
+more information for debugging, use %p and boot the kernel with the
+``no_hash_pointers`` parameter during debugging, which will print all %p
+addresses unmodified. If you *really* always want the unmodified address, see
+%px below.
+
+If (and only if) you are printing addresses as a content of a virtual file in
+e.g. procfs or sysfs (using e.g. seq_printf(), not printk()) read by a
+userspace process, use the %pK modifier described below instead of %p or %px.
 
 Error Pointers
 --------------
@@ -139,6 +151,11 @@ For printing kernel pointers which should be hidden from unprivileged
 users. The behaviour of %pK depends on the kptr_restrict sysctl - see
 Documentation/admin-guide/sysctl/kernel.rst for more details.
 
+This modifier is *only* intended when producing content of a file read by
+userspace from e.g. procfs or sysfs, not for dmesg. Please refer to the
+section about %p above for discussion about how to manage hashing pointers
+in printk().
+
 Unmodified Addresses
 --------------------
 
@@ -153,6 +170,13 @@ equivalent to %lx (or %lu). %px is preferred because it is more uniquely
 grep'able. If in the future we need to modify the way the kernel handles
 printing pointers we will be better equipped to find the call sites.
 
+Before using %px, consider if using %p is sufficient together with enabling the
+``no_hash_pointers`` kernel parameter during debugging sessions (see the %p
+description above). One valid scenario for %px might be printing information
+immediately before a panic, which prevents any sensitive information to be
+exploited anyway, and with %px there would be no need to reproduce the panic
+with no_hash_pointers.
+
 Pointer Differences
 -------------------
 
@@ -540,7 +564,7 @@ Flags bitfields such as page flags, gfp_flags
 
 ::
 
-	%pGp	referenced|uptodate|lru|active|private
+	%pGp	referenced|uptodate|lru|active|private|node=0|zone=2|lastcpupid=0x1fffff
 	%pGg	GFP_USER|GFP_DMA32|GFP_NOWARN
 	%pGv	read|exec|mayread|maywrite|mayexec|denywrite
 

MAINTAINERS

@@ -14535,7 +14535,7 @@ F:	kernel/sched/psi.c
 
 PRINTK
 M:	Petr Mladek <[email protected]>
-M:	Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
+M:	Sergey Senozhatsky <senozhatsky@chromium.org>
 R:	Steven Rostedt <[email protected]>
 R:	John Ogness <[email protected]>
 S:	Maintained
@@ -19388,7 +19388,7 @@ F:	drivers/net/vrf.c
 VSPRINTF
 M:	Petr Mladek <[email protected]>
 M:	Steven Rostedt <[email protected]>
-M:	Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
+M:	Sergey Senozhatsky <senozhatsky@chromium.org>
 R:	Andy Shevchenko <[email protected]>
 R:	Rasmus Villemoes <[email protected]>
 S:	Maintained
@@ -20039,7 +20039,7 @@ F:	drivers/staging/media/zoran/
 ZRAM COMPRESSED RAM BLOCK DEVICE DRVIER
 M:	Minchan Kim <[email protected]>
 M:	Nitin Gupta <[email protected]>
-R:	Sergey Senozhatsky <sergey.senozhatsky[email protected]>
+R:	Sergey Senozhatsky <senozhatsky@chromium.org>
 L:	[email protected]
 S:	Maintained
 F:	Documentation/admin-guide/blockdev/zram.rst
@@ -20053,7 +20053,7 @@ F:	drivers/tty/serial/zs.*
 ZSMALLOC COMPRESSED SLAB MEMORY ALLOCATOR
 M:	Minchan Kim <[email protected]>
 M:	Nitin Gupta <[email protected]>
-R:	Sergey Senozhatsky <sergey.senozhatsky[email protected]>
+R:	Sergey Senozhatsky <senozhatsky@chromium.org>
 L:	[email protected]
 S:	Maintained
 F:	Documentation/vm/zsmalloc.rst

arch/powerpc/kernel/nvram_64.c

@@ -647,6 +647,7 @@ static void oops_to_nvram(struct kmsg_dumper *dumper,
 {
 	struct oops_log_info *oops_hdr = (struct oops_log_info *)oops_buf;
 	static unsigned int oops_count = 0;
+	static struct kmsg_dump_iter iter;
 	static bool panicking = false;
 	static DEFINE_SPINLOCK(lock);
 	unsigned long flags;
@@ -681,13 +682,14 @@ static void oops_to_nvram(struct kmsg_dumper *dumper,
 		return;
 
 	if (big_oops_buf) {
-		kmsg_dump_get_buffer(dumper, false,
+		kmsg_dump_rewind(&iter);
+		kmsg_dump_get_buffer(&iter, false,
 				     big_oops_buf, big_oops_buf_sz, &text_len);
 		rc = zip_oops(text_len);
 	}
 	if (rc != 0) {
-		kmsg_dump_rewind(dumper);
-		kmsg_dump_get_buffer(dumper, false,
+		kmsg_dump_rewind(&iter);
+		kmsg_dump_get_buffer(&iter, false,
 				     oops_data, oops_data_sz, &text_len);
 		err_type = ERR_TYPE_KERNEL_PANIC;
 		oops_hdr->version = cpu_to_be16(OOPS_HDR_VERSION);

arch/powerpc/xmon/xmon.c

@@ -3001,7 +3001,7 @@ print_address(unsigned long addr)
 static void
 dump_log_buf(void)
 {
-	struct kmsg_dumper dumper = { .active = 1 };
+	struct kmsg_dump_iter iter;
 	unsigned char buf[128];
 	size_t len;
 
@@ -3013,9 +3013,9 @@ dump_log_buf(void)
 	catch_memory_errors = 1;
 	sync();
 
-	kmsg_dump_rewind_nolock(&dumper);
+	kmsg_dump_rewind(&iter);
 	xmon_start_pagination();
-	while (kmsg_dump_get_line_nolock(&dumper, false, buf, sizeof(buf), &len)) {
+	while (kmsg_dump_get_line(&iter, false, buf, sizeof(buf), &len)) {
 		buf[len] = '\0';
 		printf("%s", buf);
 	}

arch/um/kernel/kmsg_dump.c

@@ -1,5 +1,6 @@
 // SPDX-License-Identifier: GPL-2.0
 #include <linux/kmsg_dump.h>
+#include <linux/spinlock.h>
 #include <linux/console.h>
 #include <linux/string.h>
 #include <shared/init.h>
@@ -9,8 +10,11 @@
 static void kmsg_dumper_stdout(struct kmsg_dumper *dumper,
 				enum kmsg_dump_reason reason)
 {
+	static struct kmsg_dump_iter iter;
+	static DEFINE_SPINLOCK(lock);
 	static char line[1024];
 	struct console *con;
+	unsigned long flags;
 	size_t len = 0;
 
 	/* only dump kmsg when no console is available */
@@ -29,11 +33,18 @@ static void kmsg_dumper_stdout(struct kmsg_dumper *dumper,
 	if (con)
 		return;
 
+	if (!spin_trylock_irqsave(&lock, flags))
+		return;
+
+	kmsg_dump_rewind(&iter);
+
 	printf("kmsg_dump:\n");
-	while (kmsg_dump_get_line(dumper, true, line, sizeof(line), &len)) {
+	while (kmsg_dump_get_line(&iter, true, line, sizeof(line), &len)) {
 		line[len] = '\0';
 		printf("%s", line);
 	}
+
+	spin_unlock_irqrestore(&lock, flags);
 }
 
 static struct kmsg_dumper kmsg_dumper = {

drivers/hv/vmbus_drv.c

@@ -1399,6 +1399,7 @@ static irqreturn_t vmbus_percpu_isr(int irq, void *dev_id)
 static void hv_kmsg_dump(struct kmsg_dumper *dumper,
 			 enum kmsg_dump_reason reason)
 {
+	struct kmsg_dump_iter iter;
 	size_t bytes_written;
 
 	/* We are only interested in panics. */
@@ -1409,7 +1410,8 @@ static void hv_kmsg_dump(struct kmsg_dumper *dumper,
 	 * Write dump contents to the page. No need to synchronize; panic should
 	 * be single-threaded.
 	 */
-	kmsg_dump_get_buffer(dumper, false, hv_panic_page, HV_HYP_PAGE_SIZE,
+	kmsg_dump_rewind(&iter);
+	kmsg_dump_get_buffer(&iter, false, hv_panic_page, HV_HYP_PAGE_SIZE,
 			     &bytes_written);
 	if (!bytes_written)
 		return;

drivers/mtd/mtdoops.c

@@ -52,6 +52,7 @@ static struct mtdoops_context {
 	int nextcount;
 	unsigned long *oops_page_used;
 
+	unsigned long oops_buf_busy;
 	void *oops_buf;
 } oops_cxt;
 
@@ -180,6 +181,9 @@ static void mtdoops_write(struct mtdoops_context *cxt, int panic)
 	u32 *hdr;
 	int ret;
 
+	if (test_and_set_bit(0, &cxt->oops_buf_busy))
+		return;
+
 	/* Add mtdoops header to the buffer */
 	hdr = cxt->oops_buf;
 	hdr[0] = cxt->nextcount;
@@ -190,7 +194,7 @@ static void mtdoops_write(struct mtdoops_context *cxt, int panic)
 				      record_size, &retlen, cxt->oops_buf);
 		if (ret == -EOPNOTSUPP) {
 			printk(KERN_ERR "mtdoops: Cannot write from panic without panic_write\n");
-			return;
+			goto out;
 		}
 	} else
 		ret = mtd_write(mtd, cxt->nextpage * record_size,
@@ -203,6 +207,8 @@ static void mtdoops_write(struct mtdoops_context *cxt, int panic)
 	memset(cxt->oops_buf, 0xff, record_size);
 
 	mtdoops_inc_counter(cxt);
+out:
+	clear_bit(0, &cxt->oops_buf_busy);
 }
 
 static void mtdoops_workfunc_write(struct work_struct *work)
@@ -271,13 +277,19 @@ static void mtdoops_do_dump(struct kmsg_dumper *dumper,
 {
 	struct mtdoops_context *cxt = container_of(dumper,
 			struct mtdoops_context, dump);
+	struct kmsg_dump_iter iter;
 
 	/* Only dump oopses if dump_oops is set */
 	if (reason == KMSG_DUMP_OOPS && !dump_oops)
 		return;
 
-	kmsg_dump_get_buffer(dumper, true, cxt->oops_buf + MTDOOPS_HEADER_SIZE,
+	kmsg_dump_rewind(&iter);
+
+	if (test_and_set_bit(0, &cxt->oops_buf_busy))
+		return;
+	kmsg_dump_get_buffer(&iter, true, cxt->oops_buf + MTDOOPS_HEADER_SIZE,
 			     record_size - MTDOOPS_HEADER_SIZE, NULL);
+	clear_bit(0, &cxt->oops_buf_busy);
 
 	if (reason != KMSG_DUMP_OOPS) {
 		/* Panics must be written immediately */
@@ -394,6 +406,7 @@ static int __init mtdoops_init(void)
 		return -ENOMEM;
 	}
 	memset(cxt->oops_buf, 0xff, record_size);
+	cxt->oops_buf_busy = 0;
 
 	INIT_WORK(&cxt->work_erase, mtdoops_workfunc_erase);
 	INIT_WORK(&cxt->work_write, mtdoops_workfunc_write);

fs/pstore/platform.c

@@ -385,6 +385,7 @@ void pstore_record_init(struct pstore_record *record,
 static void pstore_dump(struct kmsg_dumper *dumper,
 			enum kmsg_dump_reason reason)
 {
+	struct kmsg_dump_iter iter;
 	unsigned long	total = 0;
 	const char	*why;
 	unsigned int	part = 1;
@@ -405,6 +406,8 @@ static void pstore_dump(struct kmsg_dumper *dumper,
 		}
 	}
 
+	kmsg_dump_rewind(&iter);
+
 	oopscount++;
 	while (total < kmsg_bytes) {
 		char *dst;
@@ -435,7 +438,7 @@ static void pstore_dump(struct kmsg_dumper *dumper,
 		dst_size -= header_size;
 
 		/* Write dump contents. */
-		if (!kmsg_dump_get_buffer(dumper, true, dst + header_size,
+		if (!kmsg_dump_get_buffer(&iter, true, dst + header_size,
 					  dst_size, &dump_size))
 			break;
 

include/linux/kmsg_dump.h

@@ -29,6 +29,16 @@ enum kmsg_dump_reason {
 	KMSG_DUMP_MAX
 };
 
+/**
+ * struct kmsg_dump_iter - iterator for retrieving kernel messages
+ * @cur_seq:	Points to the oldest message to dump
+ * @next_seq:	Points after the newest message to dump
+ */
+struct kmsg_dump_iter {
+	u64	cur_seq;
+	u64	next_seq;
+};
+
 /**
  * struct kmsg_dumper - kernel crash message dumper structure
  * @list:	Entry in the dumper list (private)
@@ -41,31 +51,19 @@ struct kmsg_dumper {
 	struct list_head list;
 	void (*dump)(struct kmsg_dumper *dumper, enum kmsg_dump_reason reason);
 	enum kmsg_dump_reason max_reason;
-	bool active;
 	bool registered;
-
-	/* private state of the kmsg iterator */
-	u32 cur_idx;
-	u32 next_idx;
-	u64 cur_seq;
-	u64 next_seq;
 };
 
 #ifdef CONFIG_PRINTK
 void kmsg_dump(enum kmsg_dump_reason reason);
 
-bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper, bool syslog,
-			       char *line, size_t size, size_t *len);
-
-bool kmsg_dump_get_line(struct kmsg_dumper *dumper, bool syslog,
+bool kmsg_dump_get_line(struct kmsg_dump_iter *iter, bool syslog,
 			char *line, size_t size, size_t *len);
 
-bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
-			  char *buf, size_t size, size_t *len);
-
-void kmsg_dump_rewind_nolock(struct kmsg_dumper *dumper);
+bool kmsg_dump_get_buffer(struct kmsg_dump_iter *iter, bool syslog,
+			  char *buf, size_t size, size_t *len_out);
 
-void kmsg_dump_rewind(struct kmsg_dumper *dumper);
+void kmsg_dump_rewind(struct kmsg_dump_iter *iter);
 
 int kmsg_dump_register(struct kmsg_dumper *dumper);
 
@@ -77,30 +75,19 @@ static inline void kmsg_dump(enum kmsg_dump_reason reason)
 {
 }
 
-static inline bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper,
-					     bool syslog, const char *line,
-					     size_t size, size_t *len)
-{
-	return false;
-}
-
-static inline bool kmsg_dump_get_line(struct kmsg_dumper *dumper, bool syslog,
+static inline bool kmsg_dump_get_line(struct kmsg_dump_iter *iter, bool syslog,
 				const char *line, size_t size, size_t *len)
 {
 	return false;
 }
 
-static inline bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
+static inline bool kmsg_dump_get_buffer(struct kmsg_dump_iter *iter, bool syslog,
 					char *buf, size_t size, size_t *len)
 {
 	return false;
 }
 
-static inline void kmsg_dump_rewind_nolock(struct kmsg_dumper *dumper)
-{
-}
-
-static inline void kmsg_dump_rewind(struct kmsg_dumper *dumper)
+static inline void kmsg_dump_rewind(struct kmsg_dump_iter *iter)
 {
 }