linux-kernel - [PATCH] kexec: Make a pair of map/unmap reserved pages in error path

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Message-Id: <1456408960-12296-1-git-send-email-mhuang@redhat.com>
Date:	Thu, 25 Feb 2016 22:02:40 +0800
From:	Minfei Huang <mhuang@...hat.com>
To:	ebiederm@...ssion.com, akpm@...ux-foundation.org
Cc:	kexec@...ts.infradead.org, linux-kernel@...r.kernel.org,
	mhuang@...hat.com, Minfei Huang <mnfhuang@...il.com>
Subject: [PATCH] kexec: Make a pair of map/unmap reserved pages in error path

From: Minfei Huang <mnfhuang@...il.com>

For some arch, kexec shall map the reserved pages, then use them, when
we try to start the kdump service.

kexec may return directly, without unmaping the reserved pages, if it
fails during starting service. To fix it, we make a pair of map/unmap
reserved pages both in generic path and error path.

Signed-off-by: Minfei Huang <mnfhuang@...il.com>
---
 kernel/kexec.c | 112 ++++++++++++++++++++++++++++++++-------------------------
 1 file changed, 63 insertions(+), 49 deletions(-)

diff --git a/kernel/kexec.c b/kernel/kexec.c
index ee70aef..48cf69c 100644
--- a/kernel/kexec.c
+++ b/kernel/kexec.c
@@ -103,6 +103,68 @@ out_free_image:
 	return ret;
 }
 
+static int do_kexec_load(unsigned long entry, unsigned long nr_segments,
+		struct kexec_segment __user *segments, unsigned long flags)
+{
+	struct kimage **dest_image, *image;
+	unsigned long i;
+	int ret;
+
+	if (flags & KEXEC_ON_CRASH)
+		dest_image = &kexec_crash_image;
+	else
+		dest_image = &kexec_image;
+
+	if (nr_segments == 0) {
+		/* Uninstall image */
+		kimage_free(xchg(dest_image, NULL));
+		return 0;
+	}
+	if (flags & KEXEC_ON_CRASH) {
+		/*
+		 * Loading another kernel to switch to if this one
+		 * crashes.  Free any current crash dump kernel before
+		 * we corrupt it.
+		 */
+		kimage_free(xchg(&kexec_crash_image, NULL));
+	}
+
+	ret = kimage_alloc_init(&image, entry, nr_segments, segments, flags);
+	if (ret)
+		return ret;
+
+	if (flags & KEXEC_ON_CRASH)
+		crash_map_reserved_pages();
+
+	if (flags & KEXEC_PRESERVE_CONTEXT)
+		image->preserve_context = 1;
+
+	ret = machine_kexec_prepare(image);
+	if (ret)
+		goto out;
+
+	for (i = 0; i < nr_segments; i++) {
+		ret = kimage_load_segment(image, &image->segment[i]);
+		if (ret)
+			goto out;
+	}
+
+	kimage_terminate(image);
+
+	/* Install the new kernel and uninstall the old */
+	image = xchg(dest_image, image);
+
+out:
+	/*
+	 * Once the reserved memory is mapped, we should unmap this memory
+	 * before returning
+	 */
+	if (flags & KEXEC_ON_CRASH)
+		crash_unmap_reserved_pages();
+	kimage_free(image);
+	return ret;
+}
+
 /*
  * Exec Kernel system call: for obvious reasons only root may call it.
  *
@@ -127,7 +189,6 @@ out_free_image:
 SYSCALL_DEFINE4(kexec_load, unsigned long, entry, unsigned long, nr_segments,
 		struct kexec_segment __user *, segments, unsigned long, flags)
 {
-	struct kimage **dest_image, *image;
 	int result;
 
 	/* We only trust the superuser with rebooting the system. */
@@ -152,9 +213,6 @@ SYSCALL_DEFINE4(kexec_load, unsigned long, entry, unsigned long, nr_segments,
 	if (nr_segments > KEXEC_SEGMENT_MAX)
 		return -EINVAL;
 
-	image = NULL;
-	result = 0;
-
 	/* Because we write directly to the reserved memory
 	 * region when loading crash kernels we need a mutex here to
 	 * prevent multiple crash  kernels from attempting to load
@@ -166,53 +224,9 @@ SYSCALL_DEFINE4(kexec_load, unsigned long, entry, unsigned long, nr_segments,
 	if (!mutex_trylock(&kexec_mutex))
 		return -EBUSY;
 
-	dest_image = &kexec_image;
-	if (flags & KEXEC_ON_CRASH)
-		dest_image = &kexec_crash_image;
-	if (nr_segments > 0) {
-		unsigned long i;
-
-		if (flags & KEXEC_ON_CRASH) {
-			/*
-			 * Loading another kernel to switch to if this one
-			 * crashes.  Free any current crash dump kernel before
-			 * we corrupt it.
-			 */
-
-			kimage_free(xchg(&kexec_crash_image, NULL));
-			result = kimage_alloc_init(&image, entry, nr_segments,
-						   segments, flags);
-			crash_map_reserved_pages();
-		} else {
-			/* Loading another kernel to reboot into. */
-
-			result = kimage_alloc_init(&image, entry, nr_segments,
-						   segments, flags);
-		}
-		if (result)
-			goto out;
-
-		if (flags & KEXEC_PRESERVE_CONTEXT)
-			image->preserve_context = 1;
-		result = machine_kexec_prepare(image);
-		if (result)
-			goto out;
-
-		for (i = 0; i < nr_segments; i++) {
-			result = kimage_load_segment(image, &image->segment[i]);
-			if (result)
-				goto out;
-		}
-		kimage_terminate(image);
-		if (flags & KEXEC_ON_CRASH)
-			crash_unmap_reserved_pages();
-	}
-	/* Install the new kernel, and  Uninstall the old */
-	image = xchg(dest_image, image);
+	result = do_kexec_load(entry, nr_segments, segments, flags);
 
-out:
 	mutex_unlock(&kexec_mutex);
-	kimage_free(image);
 
 	return result;
 }
-- 
2.1.0