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Subject[GIT PULL] writeback fixes

Linus,

Please pull 4 writeback fixes for

- 1 divide error
- 3 NULL dereference bugs in writeback tracing, when SD card is removed w/o umount

Thanks,
Fengguang

The following changes since commit 62aa2b537c6f5957afd98e29f96897419ed5ebab:

Linux 3.3-rc2 (2012-01-31 13:31:54 -0800)

are available in the git repository at:
git://git.kernel.org/pub/scm/linux/kernel/git/wfg/linux.git writeback-fixes

Rabin Vincent (1):
backing-dev: fix wakeup timer races with bdi_unregister()

Wu Fengguang (3):
writeback: fix NULL bdi->dev in trace writeback_single_inode
lib: proportion: lower PROP_MAX_SHIFT to 32 on 64-bit kernel
writeback: fix dereferencing NULL bdi->dev on trace_writeback_queue

fs/fs-writeback.c | 16 ++++++++--------
include/linux/proportions.h | 4 ++++
include/trace/events/writeback.h | 7 +++++--
mm/backing-dev.c | 23 ++++++++++++++++++-----
4 files changed, 35 insertions(+), 15 deletions(-)

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index f855916..5b4a936 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -53,14 +53,6 @@ struct wb_writeback_work {
};

/*
- * Include the creation of the trace points after defining the
- * wb_writeback_work structure so that the definition remains local to this
- * file.
- */
-#define CREATE_TRACE_POINTS
-#include <trace/events/writeback.h>
-
-/*
* We don't actually have pdflush, but this one is exported though /proc...
*/
int nr_pdflush_threads;
@@ -92,6 +84,14 @@ static inline struct inode *wb_inode(struct list_head *head)
return list_entry(head, struct inode, i_wb_list);
}

+/*
+ * Include the creation of the trace points after defining the
+ * wb_writeback_work structure and inline functions so that the definition
+ * remains local to this file.
+ */
+#define CREATE_TRACE_POINTS
+#include <trace/events/writeback.h>
+
/* Wakeup flusher thread or forker thread to fork it. Requires bdi->wb_lock. */
static void bdi_wakeup_flusher(struct backing_dev_info *bdi)
{
diff --git a/include/linux/proportions.h b/include/linux/proportions.h
index ef35bb7..26a8a4e 100644
--- a/include/linux/proportions.h
+++ b/include/linux/proportions.h
@@ -81,7 +81,11 @@ void prop_inc_percpu(struct prop_descriptor *pd, struct prop_local_percpu *pl)
* Limit the time part in order to ensure there are some bits left for the
* cycle counter and fraction multiply.
*/
+#if BITS_PER_LONG == 32
#define PROP_MAX_SHIFT (3*BITS_PER_LONG/4)
+#else
+#define PROP_MAX_SHIFT (BITS_PER_LONG/2)
+#endif

#define PROP_FRAC_SHIFT (BITS_PER_LONG - PROP_MAX_SHIFT - 1)
#define PROP_FRAC_BASE (1UL << PROP_FRAC_SHIFT)
diff --git a/include/trace/events/writeback.h b/include/trace/events/writeback.h
index 8588a89..5973410 100644
--- a/include/trace/events/writeback.h
+++ b/include/trace/events/writeback.h
@@ -47,7 +47,10 @@ DECLARE_EVENT_CLASS(writeback_work_class,
__field(int, reason)
),
TP_fast_assign(
- strncpy(__entry->name, dev_name(bdi->dev), 32);
+ struct device *dev = bdi->dev;
+ if (!dev)
+ dev = default_backing_dev_info.dev;
+ strncpy(__entry->name, dev_name(dev), 32);
__entry->nr_pages = work->nr_pages;
__entry->sb_dev = work->sb ? work->sb->s_dev : 0;
__entry->sync_mode = work->sync_mode;
@@ -426,7 +429,7 @@ DECLARE_EVENT_CLASS(writeback_single_inode_template,

TP_fast_assign(
strncpy(__entry->name,
- dev_name(inode->i_mapping->backing_dev_info->dev), 32);
+ dev_name(inode_to_bdi(inode)->dev), 32);
__entry->ino = inode->i_ino;
__entry->state = inode->i_state;
__entry->dirtied_when = inode->dirtied_when;
diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index 7ba8fea..dd8e2aa 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -318,7 +318,7 @@ static void wakeup_timer_fn(unsigned long data)
if (bdi->wb.task) {
trace_writeback_wake_thread(bdi);
wake_up_process(bdi->wb.task);
- } else {
+ } else if (bdi->dev) {
/*
* When bdi tasks are inactive for long time, they are killed.
* In this case we have to wake-up the forker thread which
@@ -584,6 +584,8 @@ EXPORT_SYMBOL(bdi_register_dev);
*/
static void bdi_wb_shutdown(struct backing_dev_info *bdi)
{
+ struct task_struct *task;
+
if (!bdi_cap_writeback_dirty(bdi))
return;

@@ -602,8 +604,13 @@ static void bdi_wb_shutdown(struct backing_dev_info *bdi)
* Finally, kill the kernel thread. We don't need to be RCU
* safe anymore, since the bdi is gone from visibility.
*/
- if (bdi->wb.task)
- kthread_stop(bdi->wb.task);
+ spin_lock_bh(&bdi->wb_lock);
+ task = bdi->wb.task;
+ bdi->wb.task = NULL;
+ spin_unlock_bh(&bdi->wb_lock);
+
+ if (task)
+ kthread_stop(task);
}

/*
@@ -623,7 +630,9 @@ static void bdi_prune_sb(struct backing_dev_info *bdi)

void bdi_unregister(struct backing_dev_info *bdi)
{
- if (bdi->dev) {
+ struct device *dev = bdi->dev;
+
+ if (dev) {
bdi_set_min_ratio(bdi, 0);
trace_writeback_bdi_unregister(bdi);
bdi_prune_sb(bdi);
@@ -632,8 +641,12 @@ void bdi_unregister(struct backing_dev_info *bdi)
if (!bdi_cap_flush_forker(bdi))
bdi_wb_shutdown(bdi);
bdi_debug_unregister(bdi);
- device_unregister(bdi->dev);
+
+ spin_lock_bh(&bdi->wb_lock);
bdi->dev = NULL;
+ spin_unlock_bh(&bdi->wb_lock);
+
+ device_unregister(dev);
}
}
EXPORT_SYMBOL(bdi_unregister);

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