proc/kcore: replace kclist_lock rwlock with rwsem

Now we only need kclist_lock from user context and at fs init time, and
the following changes need to sleep while holding the kclist_lock.

Link: http://lkml.kernel.org/r/521ba449ebe921d905177410fee9222d07882f0d.1531953780.git.osandov@fb.com
Signed-off-by: Omar Sandoval <osandov@fb.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Bhupesh Sharma <bhsharma@redhat.com>
Cc: Eric Biederman <ebiederm@xmission.com>
Cc: James Morse <james.morse@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/proc/kcore.c

@@ -59,7 +59,7 @@ struct memelfnote
 };
 
 static LIST_HEAD(kclist_head);
-static DEFINE_RWLOCK(kclist_lock);
+static DECLARE_RWSEM(kclist_lock);
 static int kcore_need_update = 1;
 
 /* This doesn't grab kclist_lock, so it should only be used at init time. */
@@ -117,7 +117,7 @@ static void __kcore_update_ram(struct list_head *list)
 	struct kcore_list *tmp, *pos;
 	LIST_HEAD(garbage);
 
-	write_lock(&kclist_lock);
+	down_write(&kclist_lock);
 	if (xchg(&kcore_need_update, 0)) {
 		list_for_each_entry_safe(pos, tmp, &kclist_head, list) {
 			if (pos->type == KCORE_RAM
@@ -128,7 +128,7 @@ static void __kcore_update_ram(struct list_head *list)
 	} else
 		list_splice(list, &garbage);
 	proc_root_kcore->size = get_kcore_size(&nphdr, &size);
-	write_unlock(&kclist_lock);
+	up_write(&kclist_lock);
 
 	free_kclist_ents(&garbage);
 }
@@ -451,11 +451,11 @@ read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos)
 	int nphdr;
 	unsigned long start;
 
-	read_lock(&kclist_lock);
+	down_read(&kclist_lock);
 	size = get_kcore_size(&nphdr, &elf_buflen);
 
 	if (buflen == 0 || *fpos >= size) {
-		read_unlock(&kclist_lock);
+		up_read(&kclist_lock);
 		return 0;
 	}
 
@@ -472,11 +472,11 @@ read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos)
 			tsz = buflen;
 		elf_buf = kzalloc(elf_buflen, GFP_ATOMIC);
 		if (!elf_buf) {
-			read_unlock(&kclist_lock);
+			up_read(&kclist_lock);
 			return -ENOMEM;
 		}
 		elf_kcore_store_hdr(elf_buf, nphdr, elf_buflen);
-		read_unlock(&kclist_lock);
+		up_read(&kclist_lock);
 		if (copy_to_user(buffer, elf_buf + *fpos, tsz)) {
 			kfree(elf_buf);
 			return -EFAULT;
@@ -491,7 +491,7 @@ read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos)
 		if (buflen == 0)
 			return acc;
 	} else
-		read_unlock(&kclist_lock);
+		up_read(&kclist_lock);
 
 	/*
 	 * Check to see if our file offset matches with any of
@@ -504,12 +504,12 @@ read_kcore(struct file *file, char __user *buffer, size_t buflen, loff_t *fpos)
 	while (buflen) {
 		struct kcore_list *m;
 
-		read_lock(&kclist_lock);
+		down_read(&kclist_lock);
 		list_for_each_entry(m, &kclist_head, list) {
 			if (start >= m->addr && start < (m->addr+m->size))
 				break;
 		}
-		read_unlock(&kclist_lock);
+		up_read(&kclist_lock);
 
 		if (&m->list == &kclist_head) {
 			if (clear_user(buffer, tsz))