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drbd: fix race on meta-data update, addendum 

addendum to baa33ae4eaa4477b60af7c434c0ddd1d182c1ae7

The race:
    drbd_md_sync()
	if (!test_and_clear_bit(MD_DIRTY, &mdev->flags))
		return;
    ==> RACE with drbd_md_mark_dirty() rearming the timer.
	del_timer(&mdev->md_sync_timer);

    Fixed by moving the del_timer before the test_and_clear_bit.

Additionally only rearm the timer in drbd_md_mark_dirty, if MD_DIRTY was
not already set, reduce the grace period from five to one second, and
add an ifdef'ed debuging aid to find code paths missing an explicit
drbd_md_sync, if any, as those are the only relevant ones for this race.

Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>
This commit is contained in:
Lars Ellenberg 2010-09-03 10:00:09 +02:00 committed by Philipp Reisner
parent 63106d3c6c
commit ee15b03816
2 changed files with 31 additions and 5 deletions
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12
drivers/block/drbd/drbd_int.h
View File

@ -975,6 +975,12 @@ struct drbd_conf {
md_sync_work;
struct timer_list resync_timer;
struct timer_list md_sync_timer;
#ifdef DRBD_DEBUG_MD_SYNC
struct {
unsigned int line;
const char* func;
} last_md_mark_dirty;
#endif
/* Used after attach while negotiating new disk state. */
union drbd_state new_state_tmp;
@ -1253,7 +1259,13 @@ extern void drbd_uuid_set_bm(struct drbd_conf *mdev, u64 val) __must_hold(local)
extern void drbd_md_set_flag(struct drbd_conf *mdev, int flags) __must_hold(local);
extern void drbd_md_clear_flag(struct drbd_conf *mdev, int flags)__must_hold(local);
extern int drbd_md_test_flag(struct drbd_backing_dev *, int);
#ifndef DRBD_DEBUG_MD_SYNC
extern void drbd_md_mark_dirty(struct drbd_conf *mdev);
#else
#define drbd_md_mark_dirty(m) drbd_md_mark_dirty_(m, __LINE__ , __func__ )
extern void drbd_md_mark_dirty_(struct drbd_conf *mdev,
unsigned int line, const char *func);
#endif
extern void drbd_queue_bitmap_io(struct drbd_conf *mdev,
int (*io_fn)(struct drbd_conf *),
void (*done)(struct drbd_conf *, int),

24
drivers/block/drbd/drbd_main.c
View File

@ -3402,9 +3402,10 @@ void drbd_md_sync(struct drbd_conf *mdev)
sector_t sector;
int i;
del_timer(&mdev->md_sync_timer);
/* timer may be rearmed by drbd_md_mark_dirty() now. */
if (!test_and_clear_bit(MD_DIRTY, &mdev->flags))
return;
del_timer(&mdev->md_sync_timer);
/* We use here D_FAILED and not D_ATTACHING because we try to write
* metadata even if we detach due to a disk failure! */
@ -3529,12 +3530,22 @@ int drbd_md_read(struct drbd_conf *mdev, struct drbd_backing_dev *bdev)
* the meta-data super block. This function sets MD_DIRTY, and starts a
* timer that ensures that within five seconds you have to call drbd_md_sync().
*/
#ifdef DRBD_DEBUG_MD_SYNC
void drbd_md_mark_dirty_(struct drbd_conf *mdev, unsigned int line, const char *func)
{
if (!test_and_set_bit(MD_DIRTY, &mdev->flags)) {
mod_timer(&mdev->md_sync_timer, jiffies + HZ);
mdev->last_md_mark_dirty.line = line;
mdev->last_md_mark_dirty.func = func;
}
}
#else
void drbd_md_mark_dirty(struct drbd_conf *mdev)
{
set_bit(MD_DIRTY, &mdev->flags);
mod_timer(&mdev->md_sync_timer, jiffies + 5*HZ);
if (!test_and_set_bit(MD_DIRTY, &mdev->flags))
mod_timer(&mdev->md_sync_timer, jiffies + HZ);
}
#endif
static void drbd_uuid_move_history(struct drbd_conf *mdev) __must_hold(local)
{
@ -3775,8 +3786,11 @@ static void md_sync_timer_fn(unsigned long data)
static int w_md_sync(struct drbd_conf *mdev, struct drbd_work *w, int unused)
{
dev_warn(DEV, "md_sync_timer expired! Worker calls drbd_md_sync().\n");
#ifdef DEBUG
dev_warn(DEV, "last md_mark_dirty: %s:%u\n",
mdev->last_md_mark_dirty.func, mdev->last_md_mark_dirty.line);
#endif
drbd_md_sync(mdev);
return 1;
}