iterate_supers() calls a function provided by the caller with the s_umount
semaphore taken in read mode. However, there may be cases where write mode
is preferable, so we add __iterate_supers(), which lets one
specify the mode of the lock, and replace iterate_supers with two helpers
around __iterate_supers(), iterate_supers_read() and iterate_supers_write().
This will be used to fix the emergency thaw (filesystem unfreeze) code, which
iterates over the list of superblocks but needs to hold the s_umount semaphore
in _write_ mode bebore carrying out the actual thaw operation.
This patch introduces no semantic changes since iterate_supers() users become
iterate_supers_read() which is equivalent.
Cc: Josef Bacik <jbacik@xxxxxxxxxxxx>
Cc: Eric Sandeen <sandeen@xxxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Cc: Jan Kara <jack@xxxxxxx>
Cc: Dave Chinner <dchinner@xxxxxxxxxx>
Signed-off-by: Fernando Luis Vazquez Cao <fernando@xxxxxxxxxxxxx>
---
diff -urNp linux-3.6-rc5-orig/fs/buffer.c linux-3.6-rc5/fs/buffer.c
--- linux-3.6-rc5-orig/fs/buffer.c 2012-09-14 11:53:42.972703234 +0900
+++ linux-3.6-rc5/fs/buffer.c 2012-09-14 12:02:04.892713525 +0900
@@ -521,7 +521,7 @@ static void do_thaw_one(struct super_blo
static void do_thaw_all(struct work_struct *work)
{
- iterate_supers(do_thaw_one, NULL);
+ iterate_supers_read(do_thaw_one, NULL);
kfree(work);
printk(KERN_WARNING "Emergency Thaw complete\n");
}
diff -urNp linux-3.6-rc5-orig/fs/drop_caches.c linux-3.6-rc5/fs/drop_caches.c
--- linux-3.6-rc5-orig/fs/drop_caches.c 2012-07-22 05:58:29.000000000 +0900
+++ linux-3.6-rc5/fs/drop_caches.c 2012-09-14 12:01:30.524713362 +0900
@@ -59,7 +59,7 @@ int drop_caches_sysctl_handler(ctl_table
return ret;
if (write) {
if (sysctl_drop_caches & 1)
- iterate_supers(drop_pagecache_sb, NULL);
+ iterate_supers_read(drop_pagecache_sb, NULL);
if (sysctl_drop_caches & 2)
drop_slab();
}
diff -urNp linux-3.6-rc5-orig/fs/quota/quota.c linux-3.6-rc5/fs/quota/quota.c
--- linux-3.6-rc5-orig/fs/quota/quota.c 2012-09-14 11:53:43.388703307 +0900
+++ linux-3.6-rc5/fs/quota/quota.c 2012-09-14 12:00:31.568712693 +0900
@@ -58,7 +58,7 @@ static int quota_sync_all(int type)
return -EINVAL;
ret = security_quotactl(Q_SYNC, type, 0, NULL);
if (!ret)
- iterate_supers(quota_sync_one, &type);
+ iterate_supers_read(quota_sync_one, &type);
return ret;
}
diff -urNp linux-3.6-rc5-orig/fs/super.c linux-3.6-rc5/fs/super.c
--- linux-3.6-rc5-orig/fs/super.c 2012-09-14 11:53:43.416703312 +0900
+++ linux-3.6-rc5/fs/super.c 2012-09-14 12:30:52.188833193 +0900
@@ -537,14 +537,22 @@ void drop_super(struct super_block *sb)
EXPORT_SYMBOL(drop_super);
/**
- * iterate_supers - call function for all active superblocks
+ * __iterate_supers - call function for all active superblocks
* @f: function to call
* @arg: argument to pass to it
+ * @wlock: mode of superblock lock (false->read lock, true->write lock)
*
* Scans the superblock list and calls given function, passing it
* locked superblock and given argument.
+ *
+ * When the caller asks for the superblock lock (s_umount semaphore) to be
+ * taken in write mode, the lock is taken but not released because the
+ * function provided by the caller may deactivate the superblock itself.
+ * It is that function's job to unlock the superblock as needed in such a
+ * case.
*/
-void iterate_supers(void (*f)(struct super_block *, void *), void *arg)
+static void __iterate_supers(void (*f)(struct super_block *, void *), void *arg,
+ bool wlock)
{
struct super_block *sb, *p = NULL;
@@ -555,10 +563,19 @@ void iterate_supers(void (*f)(struct sup
sb->s_count++;
spin_unlock(&sb_lock);
- down_read(&sb->s_umount);
+ if (wlock)
+ down_write(&sb->s_umount);
+ else
+ down_read(&sb->s_umount);
+
if (sb->s_root && (sb->s_flags & MS_BORN))
f(sb, arg);
- up_read(&sb->s_umount);
+
+ /* When the semaphore was taken in write mode the function
+ * provided by the caller takes care of unlocking it as
+ * needed. See explanation above for details. */
+ if (!wlock)
+ up_read(&sb->s_umount);
spin_lock(&sb_lock);
if (p)
@@ -571,6 +588,36 @@ void iterate_supers(void (*f)(struct sup
}
/**
+ * iterate_supers_read - call function for all active superblocks
+ * @f: function to call
+ * @arg: argument to pass to it
+ *
+ * Scans the superblock list and calls given function, passing it
+ * a superblock locked in _read_ mode and given argument. The lock
+ * is automatically relased after the function return.
+ */
+void iterate_supers_read(void (*f)(struct super_block *, void *), void *arg)
+{
+ __iterate_supers(f, arg , false);
+}
+
+/**
+ * iterate_supers_write - call function for all active superblocks
+ * @f: function to call
+ * @arg: argument to pass to it
+ *
+ * Scans the superblock list and calls given function, passing it
+ * a superblock locked in _write_ mode and given argument. Diferently
+ * from its read counterpart, iterate_supers_write does not release
+ * the lock after the function return. See description of __iterate_supers
+ * above for details.
+ */
+void iterate_supers_write(void (*f)(struct super_block *, void *), void *arg)
+{
+ __iterate_supers(f, arg , true);
+}
+
+/**
* iterate_supers_type - call function for superblocks of given type
* @type: fs type
* @f: function to call
diff -urNp linux-3.6-rc5-orig/fs/sync.c linux-3.6-rc5/fs/sync.c
--- linux-3.6-rc5-orig/fs/sync.c 2012-09-14 11:53:43.416703312 +0900
+++ linux-3.6-rc5/fs/sync.c 2012-09-14 12:02:45.900713907 +0900
@@ -104,9 +104,9 @@ SYSCALL_DEFINE0(sync)
int nowait = 0, wait = 1;
wakeup_flusher_threads(0, WB_REASON_SYNC);
- iterate_supers(sync_inodes_one_sb, NULL);
- iterate_supers(sync_fs_one_sb, &nowait);
- iterate_supers(sync_fs_one_sb, &wait);
+ iterate_supers_read(sync_inodes_one_sb, NULL);
+ iterate_supers_read(sync_fs_one_sb, &nowait);
+ iterate_supers_read(sync_fs_one_sb, &wait);
iterate_bdevs(fdatawrite_one_bdev, NULL);
iterate_bdevs(fdatawait_one_bdev, NULL);
if (unlikely(laptop_mode))
@@ -122,11 +122,11 @@ static void do_sync_work(struct work_str
* Sync twice to reduce the possibility we skipped some inodes / pages
* because they were temporarily locked
*/
- iterate_supers(sync_inodes_one_sb, &nowait);
- iterate_supers(sync_fs_one_sb, &nowait);
+ iterate_supers_read(sync_inodes_one_sb, &nowait);
+ iterate_supers_read(sync_fs_one_sb, &nowait);
iterate_bdevs(fdatawrite_one_bdev, NULL);
- iterate_supers(sync_inodes_one_sb, &nowait);
- iterate_supers(sync_fs_one_sb, &nowait);
+ iterate_supers_read(sync_inodes_one_sb, &nowait);
+ iterate_supers_read(sync_fs_one_sb, &nowait);
iterate_bdevs(fdatawrite_one_bdev, NULL);
printk("Emergency Sync complete\n");
kfree(work);
diff -urNp linux-3.6-rc5-orig/include/linux/fs.h linux-3.6-rc5/include/linux/fs.h
--- linux-3.6-rc5-orig/include/linux/fs.h 2012-09-14 11:53:43.556703343 +0900
+++ linux-3.6-rc5/include/linux/fs.h 2012-09-14 12:03:50.352714271 +0900
@@ -2684,7 +2684,8 @@ extern struct super_block *get_super(str
extern struct super_block *get_super_thawed(struct block_device *);
extern struct super_block *get_active_super(struct block_device *bdev);
extern void drop_super(struct super_block *sb);
-extern void iterate_supers(void (*)(struct super_block *, void *), void *);
+extern void iterate_supers_read(void (*)(struct super_block *, void *), void *);
+extern void iterate_supers_write(void (*)(struct super_block *, void *), void *);
extern void iterate_supers_type(struct file_system_type *,
void (*)(struct super_block *, void *), void *);
diff -urNp linux-3.6-rc5-orig/security/selinux/hooks.c linux-3.6-rc5/security/selinux/hooks.c
--- linux-3.6-rc5-orig/security/selinux/hooks.c 2012-09-14 11:53:44.484703545 +0900
+++ linux-3.6-rc5/security/selinux/hooks.c 2012-09-14 12:00:14.816712518 +0900
@@ -5755,7 +5755,7 @@ void selinux_complete_init(void)
/* Set up any superblocks initialized prior to the policy load. */
printk(KERN_DEBUG "SELinux: Setting up existing superblocks.\n");
- iterate_supers(delayed_superblock_init, NULL);
+ iterate_supers_read(delayed_superblock_init, NULL);
}
/* SELinux requires early initialization in order to label
--
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