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Message-Id: <200610300029.25555.rjw@sisk.pl>
Date: Mon, 30 Oct 2006 00:29:24 +0100
From: "Rafael J. Wysocki" <rjw@...k.pl>
To: Pavel Machek <pavel@....cz>
Cc: David Chinner <dgc@....com>,
Nigel Cunningham <ncunningham@...uxmail.org>,
Andrew Morton <akpm@...l.org>,
LKML <linux-kernel@...r.kernel.org>, xfs@....sgi.com,
Christoph Hellwig <hch@...radead.org>
Subject: Re: [PATCH] Freeze bdevs when freezing processes.
Hi,
On Sunday, 29 October 2006 18:35, Pavel Machek wrote:
> Hi!
>
> > > > > As you have them at the moment, the threads seem to be freezing fine.
> > > > > The issue I've seen in the past related not to threads but to timer
> > > > > based activity. Admittedly it was 2.6.14 when I last looked at it, but
> > > > > there used to be a possibility for XFS to submit I/O from a timer when
> > > > > the threads are frozen but the bdev isn't frozen. Has that changed?
> > > >
> > > > I didn't think we've ever done that - periodic or delayed operations
> > > > are passed off to the kernel threads to execute. A stack trace
> > > > (if you still have it) would be really help here.
> > > >
> > > > Hmmm - we have a couple of per-cpu work queues as well that are
> > > > used on I/O completion and that can, in some circumstances,
> > > > trigger new transactions. If we are only flush metadata, then
> > > > I don't think that any more I/o will be issued, but I could be
> > > > wrong (maze of twisty passages).
> > >
> > > Well, I think this exactly is the problem, because worker_threads run with
> > > PF_NOFREEZE set (as I've just said in another message).
> >
> > Ok, so freezing the filesystem is the only way you can prevent
> > this as the workqueues are flushed as part of quiescing the filesystem.
>
> Well, alternative is to teach XFS to sense that we are being frozen
> and stop disk writes in such case.
>
> OTOH freeze_bdevs is perhaps not that bad solution...
Okay, appended is a patch that implements the freezing of bdevs in a slightly
different way than the Nigel's patch did it.
As Christoph suggested, I have put freeze_filesystems() and thaw_filesystems()
into fs/buffer.c and indroduced the MS_FROZEN flag to mark frozen
filesystems.
It seems to work fine, except I get the following trace from lockdep during
the suspend on a regular basis (not 100% reproducible, though):
Stopping tasks...
=============================================
[ INFO: possible recursive locking detected ]
2.6.19-rc2-mm2 #15
---------------------------------------------
s2disk/5564 is trying to acquire lock:
(&bdev->bd_mount_mutex){--..}, at: [<ffffffff80475e79>] mutex_lock+0x9/0x10
but task is already holding lock:
(&bdev->bd_mount_mutex){--..}, at: [<ffffffff80475e79>] mutex_lock+0x9/0x10
other info that might help us debug this:
3 locks held by s2disk/5564:
#0: (&bdev->bd_mount_mutex){--..}, at: [<ffffffff80475e79>] mutex_lock+0x9/0x10
#1: (&type->s_umount_key#16){----}, at: [<ffffffff80291647>] get_super+0x67/0xc0
#2: (&journal->j_barrier){--..}, at: [<ffffffff80475e79>] mutex_lock+0x9/0x10
stack backtrace:
Call Trace:
[<ffffffff8020af79>] dump_trace+0xb9/0x430
[<ffffffff8020b333>] show_trace+0x43/0x60
[<ffffffff8020b635>] dump_stack+0x15/0x20
[<ffffffff8024a1d1>] __lock_acquire+0x881/0xc60
[<ffffffff8024a94d>] lock_acquire+0x8d/0xc0
[<ffffffff80475cd4>] __mutex_lock_slowpath+0xd4/0x270
[<ffffffff80475e79>] mutex_lock+0x9/0x10
[<ffffffff802b2bb6>] freeze_bdev+0x16/0x80
[<ffffffff802b3105>] freeze_filesystems+0x55/0x80
[<ffffffff80255942>] freeze_processes+0x1e2/0x360
[<ffffffff802592a3>] snapshot_ioctl+0x163/0x610
[<ffffffff8029cf0b>] do_ioctl+0x6b/0xa0
[<ffffffff8029d1eb>] vfs_ioctl+0x2ab/0x2d0
[<ffffffff8029d27a>] sys_ioctl+0x6a/0xa0
[<ffffffff80209c2e>] system_call+0x7e/0x83
[<00002afb13a4d8a9>]
done.
Shrinking memory... done (19126 pages freed)
Greetings,
Rafael
Signed-off-by: Rafael J. Wysocki <rjw@...k.pl>
---
fs/buffer.c | 38 +++++++++++++++++++++++++++++++++
include/linux/buffer_head.h | 2 +
include/linux/fs.h | 1
kernel/power/process.c | 50 +++++++++++++++++++++++++++++---------------
4 files changed, 74 insertions(+), 17 deletions(-)
Index: linux-2.6.19-rc2-mm2/kernel/power/process.c
===================================================================
--- linux-2.6.19-rc2-mm2.orig/kernel/power/process.c
+++ linux-2.6.19-rc2-mm2/kernel/power/process.c
@@ -14,6 +14,7 @@
#include <linux/module.h>
#include <linux/syscalls.h>
#include <linux/freezer.h>
+#include <linux/buffer_head.h>
/*
* Timeout for stopping processes
@@ -119,7 +120,7 @@ int freeze_processes(void)
read_unlock(&tasklist_lock);
todo += nr_user;
if (!user_frozen && !nr_user) {
- sys_sync();
+ freeze_filesystems();
start_time = jiffies;
}
user_frozen = !nr_user;
@@ -156,28 +157,43 @@ int freeze_processes(void)
void thaw_some_processes(int all)
{
struct task_struct *g, *p;
- int pass = 0; /* Pass 0 = Kernel space, 1 = Userspace */
printk("Restarting tasks... ");
read_lock(&tasklist_lock);
- do {
- do_each_thread(g, p) {
- /*
- * is_user = 0 if kernel thread or borrowed mm,
- * 1 otherwise.
- */
- int is_user = !!(p->mm && !(p->flags & PF_BORROWED_MM));
- if (!freezeable(p) || (is_user != pass))
- continue;
- if (!thaw_process(p))
- printk(KERN_INFO
- "Strange, %s not stopped\n", p->comm);
- } while_each_thread(g, p);
- pass++;
- } while (pass < 2 && all);
+ do_each_thread(g, p) {
+ if (!freezeable(p))
+ continue;
+
+ /* Don't thaw userland processes, for now */
+ if (p->mm && !(p->flags & PF_BORROWED_MM))
+ continue;
+
+ if (!thaw_process(p))
+ printk(KERN_INFO " Strange, %s not stopped\n", p->comm );
+ } while_each_thread(g, p);
+
+ read_unlock(&tasklist_lock);
+ if (!all)
+ goto Exit;
+
+ thaw_filesystems();
+ read_lock(&tasklist_lock);
+
+ do_each_thread(g, p) {
+ if (!freezeable(p))
+ continue;
+
+ /* Kernel threads should have been thawed already */
+ if (!p->mm || (p->flags & PF_BORROWED_MM))
+ continue;
+
+ if (!thaw_process(p))
+ printk(KERN_INFO " Strange, %s not stopped\n", p->comm );
+ } while_each_thread(g, p);
read_unlock(&tasklist_lock);
+Exit:
schedule();
printk("done.\n");
}
Index: linux-2.6.19-rc2-mm2/include/linux/buffer_head.h
===================================================================
--- linux-2.6.19-rc2-mm2.orig/include/linux/buffer_head.h
+++ linux-2.6.19-rc2-mm2/include/linux/buffer_head.h
@@ -170,6 +170,8 @@ wait_queue_head_t *bh_waitq_head(struct
int fsync_bdev(struct block_device *);
struct super_block *freeze_bdev(struct block_device *);
void thaw_bdev(struct block_device *, struct super_block *);
+void freeze_filesystems(void);
+void thaw_filesystems(void);
int fsync_super(struct super_block *);
int fsync_no_super(struct block_device *);
struct buffer_head *__find_get_block(struct block_device *, sector_t, int);
Index: linux-2.6.19-rc2-mm2/include/linux/fs.h
===================================================================
--- linux-2.6.19-rc2-mm2.orig/include/linux/fs.h
+++ linux-2.6.19-rc2-mm2/include/linux/fs.h
@@ -120,6 +120,7 @@ extern int dir_notify_enable;
#define MS_PRIVATE (1<<18) /* change to private */
#define MS_SLAVE (1<<19) /* change to slave */
#define MS_SHARED (1<<20) /* change to shared */
+#define MS_FROZEN (1<<21) /* Frozen by freeze_filesystems() */
#define MS_ACTIVE (1<<30)
#define MS_NOUSER (1<<31)
Index: linux-2.6.19-rc2-mm2/fs/buffer.c
===================================================================
--- linux-2.6.19-rc2-mm2.orig/fs/buffer.c
+++ linux-2.6.19-rc2-mm2/fs/buffer.c
@@ -244,6 +244,44 @@ void thaw_bdev(struct block_device *bdev
}
EXPORT_SYMBOL(thaw_bdev);
+/**
+ * freeze_filesystems - lock all filesystems and force them into a consistent
+ * state
+ */
+void freeze_filesystems(void)
+{
+ struct super_block *sb;
+
+ /*
+ * Freeze in reverse order so filesystems dependant upon others are
+ * frozen in the right order (eg. loopback on ext3).
+ */
+ list_for_each_entry_reverse(sb, &super_blocks, s_list) {
+ if (!sb->s_root || !sb->s_bdev ||
+ (sb->s_frozen == SB_FREEZE_TRANS) ||
+ (sb->s_flags & MS_RDONLY) ||
+ (sb->s_flags & MS_FROZEN))
+ continue;
+
+ freeze_bdev(sb->s_bdev);
+ sb->s_flags |= MS_FROZEN;
+ }
+}
+
+/**
+ * thaw_filesystems - unlock all filesystems
+ */
+void thaw_filesystems(void)
+{
+ struct super_block *sb;
+
+ list_for_each_entry(sb, &super_blocks, s_list)
+ if (sb->s_flags & MS_FROZEN) {
+ sb->s_flags &= ~MS_FROZEN;
+ thaw_bdev(sb->s_bdev, sb);
+ }
+}
+
/*
* Various filesystems appear to want __find_get_block to be non-blocking.
* But it's the page lock which protects the buffers. To get around this,
-
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