[PATCH 2/4] vfs: Move autoclose of BSD accounting into a work queue

[Eric W. Biederman]

The autoclose of BSD accounting writes a record to the BSD accounting
file.  When mntput is called from moderaly deep within the stack the
(3KiB or so) generating I/O can be problemenatic as some I/O paths
require nearly 5KiB of stack on their own.

Avoid the possibility of stack overflow by moving the close of the BSD
accounting file into a work queue.

Signed-off-by: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
---
 kernel/acct.c | 25 ++++++++++++++++++++-----
 1 file changed, 20 insertions(+), 5 deletions(-)

diff --git a/kernel/acct.c b/kernel/acct.c
index 8d6e145138bb..1853dd4a1d01 100644
--- a/kernel/acct.c
+++ b/kernel/acct.c
@@ -93,6 +93,7 @@ struct bsd_acct_struct {
 
 static DEFINE_SPINLOCK(acct_lock);
 static LIST_HEAD(acct_list);
+static LIST_HEAD(acct_close_list);
 
 /*
  * Check the amount of free space and suspend/resume accordingly.
@@ -280,6 +281,20 @@ SYSCALL_DEFINE1(acct, const char __user *, name)
 	return error;
 }
 
+static void acct_close_mnts(struct work_struct *unused)
+{
+	struct bsd_acct_struct *acct;
+
+	spin_lock(&acct_lock);
+restart:
+	list_for_each_entry(acct, &acct_close_list, list) {
+		acct_file_reopen(acct, NULL, NULL);
+		goto restart;
+	}
+	spin_unlock(&acct_lock);
+}
+static DECLARE_WORK(acct_close_work, acct_close_mnts);
+
 /**
  * acct_auto_close - turn off a filesystem's accounting if it is on
  * @m: vfsmount being shut down
@@ -289,15 +304,15 @@ SYSCALL_DEFINE1(acct, const char __user *, name)
  */
 void acct_auto_close_mnt(struct vfsmount *m)
 {
-	struct bsd_acct_struct *acct;
+	struct bsd_acct_struct *acct, *tmp;
 
 	spin_lock(&acct_lock);
-restart:
-	list_for_each_entry(acct, &acct_list, list)
+	list_for_each_entry_safe(acct, tmp, &acct_list, list) {
 		if (acct->file && acct->file->f_path.mnt == m) {
-			acct_file_reopen(acct, NULL, NULL);
-			goto restart;
+			list_move_tail(&acct->list, &acct_close_list);
+			schedule_work(&acct_close_work);
 		}
+	}
 	spin_unlock(&acct_lock);
 }
 
-- 
1.9.1

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