linux-kernel - [RFC patch] vsprintf: Add %pav extension for print_vma

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Date:	Tue, 26 May 2015 16:05:04 -0700
From:	Joe Perches <joe@...ches.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	LKML <linux-kernel@...r.kernel.org>
Subject: [RFC patch] vsprintf: Add %pav extension for print_vma_addr

print_vma_addr is another function to emit useful
data similar to print_symbol.  The print_symbol
functionality has been added via %p[fFsS] vsprintf
extensions.

Perhaps it's appropriate to add vma_addr address
decoding to vsprintf too.

This would allow code conversions where the very
unlikely interleaving of messages from multiple
threads might occur.

like arch/x86/kernel/traps.c:

from:
        if (show_unhandled_signals && unhandled_signal(tsk, signr) &&
            printk_ratelimit()) {
                pr_info("%s[%d] trap %s ip:%lx sp:%lx error:%lx",
                        tsk->comm, tsk->pid, str,
                        regs->ip, regs->sp, error_code);
                print_vma_addr(" in ", regs->ip);
                pr_cont("\n");
to:
                pr_info("%s[%d] trap %s ip:%lx sp:%lx error:%lx in %pav\n",
                        regs->ip, regs->sp, error_code, &regs->ip);
        }

Something like:

---

 Documentation/printk-formats.txt |  5 ++++
 lib/vsprintf.c                   | 62 ++++++++++++++++++++++++++++++++++++----
 2 files changed, 61 insertions(+), 6 deletions(-)

diff --git a/Documentation/printk-formats.txt b/Documentation/printk-formats.txt
index 2ec6d84..962f82c 100644
--- a/Documentation/printk-formats.txt
+++ b/Documentation/printk-formats.txt
@@ -86,6 +86,11 @@ DMA addresses types dma_addr_t:
 	For printing a dma_addr_t type which can vary based on build options,
 	regardless of the width of the CPU data path. Passed by reference.
 
+VMA addresses: where the content of an unsigned long * is used in find_vma()
+	%pav	"%s[%lx+%lx]",
+	        kbasename(d_path(vma->vm_file)),
+		vma->vm_start, vma->vm_end - vma->vm_start)
+
 Raw buffer as an escaped string:
 
 	%*pE[achnops]
diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 8243e2f..f4956c1 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -1313,23 +1313,70 @@ char *netdev_feature_string(char *buf, char *end, const u8 *addr,
 }
 
 static noinline_for_stack
+char *vma_addr(char *buf, char *end, const void *addr,
+	       struct printf_spec spec, const char *fmt)
+{
+	struct mm_struct *mm = current->mm;
+	struct vm_area_struct *vma;
+	unsigned long ip = *(unsigned long *)addr;
+	char *rtn;
+
+	/* if we are in atomic contexts (in exception stacks, etc.) */
+	if (preempt_count())
+		return string(buf, end, "(atomic context)", spec);
+
+	down_read(&mm->mmap_sem);
+	vma = find_vma(mm, ip);
+	if (vma && vma->vm_file) {
+		struct file *f = vma->vm_file;
+		char *gfp_buf = (char *)__get_free_page(GFP_KERNEL);
+
+		if (gfp_buf) {
+			char *p = d_path(&f->f_path, gfp_buf, PAGE_SIZE);
+
+			if (IS_ERR(p))
+				p = "?";
+
+			rtn = buf + snprintf(buf, end > buf ? end - buf : 0,
+					     "%s[%lx+%lx]",
+					     kbasename(p),
+					     vma->vm_start,
+					     vma->vm_end - vma->vm_start);
+
+			free_page((unsigned long)gfp_buf);
+		} else {
+			rtn = string(buf, end, "(__get_free_page failed)", spec);
+		}
+	} else {
+		rtn = string(buf, end, "(find_vma failed)", spec);
+	}
+
+	up_read(&mm->mmap_sem);
+
+	return rtn;
+}
+
+static noinline_for_stack
 char *address_val(char *buf, char *end, const void *addr,
 		  struct printf_spec spec, const char *fmt)
 {
 	unsigned long long num;
 
-	spec.flags |= SPECIAL | SMALL | ZEROPAD;
-	spec.base = 16;
-
 	switch (fmt[1]) {
+	case 'v':
+		return vma_addr(buf, end, addr, spec, fmt);
 	case 'd':
-		num = *(const dma_addr_t *)addr;
+		spec.flags |= SPECIAL | SMALL | ZEROPAD;
+		spec.base = 16;
 		spec.field_width = sizeof(dma_addr_t) * 2 + 2;
+		num = *(const dma_addr_t *)addr;
 		break;
 	case 'p':
 	default:
-		num = *(const phys_addr_t *)addr;
+		spec.flags |= SPECIAL | SMALL | ZEROPAD;
+		spec.base = 16;
 		spec.field_width = sizeof(phys_addr_t) * 2 + 2;
+		num = *(const phys_addr_t *)addr;
 		break;
 	}
 
@@ -1453,7 +1500,10 @@ int kptr_restrict __read_mostly;
  *              N no separator
  *            The maximum supported length is 64 bytes of the input. Consider
  *            to use print_hex_dump() for the larger input.
- * - 'a[pd]' For address types [p] phys_addr_t, [d] dma_addr_t and derivatives
+ * - 'a[pdv]' For address types:
+ *            [p] phys_addr_t and derivatives (resource_size_t)
+ *            [d] dma_addr_t
+ *            [v] vma_addr
  *           (default assumed to be phys_addr_t, passed by reference)
  * - 'd[234]' For a dentry name (optionally 2-4 last components)
  * - 'D[234]' Same as 'd' but for a struct file


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