From 260fa034ef7a4ff8b73068b48ac497edd5217491 Mon Sep 17 00:00:00 2001 From: NeilBrown Date: Tue, 27 Aug 2013 16:44:13 +1000 Subject: md: avoid deadlock when dirty buffers during md_stop. When the last process closes /dev/mdX sync_blockdev will be called so that all buffers get flushed. So if it is then opened for the STOP_ARRAY ioctl to be sent there will be nothing to flush. However if we open /dev/mdX in order to send the STOP_ARRAY ioctl just moments before some other process which was writing closes their file descriptor, then there won't be a 'last close' and the buffers might not get flushed. So do_md_stop() calls sync_blockdev(). However at this point it is holding ->reconfig_mutex. So if the array is currently 'clean' then the writes from sync_blockdev() will not complete until the array can be marked dirty and that won't happen until some other thread can get ->reconfig_mutex. So we deadlock. We need to move the sync_blockdev() call to before we take ->reconfig_mutex. However then some other thread could open /dev/mdX and write to it after we call sync_blockdev() and before we actually stop the array. This can leave dirty data in the page cache which is awkward. So introduce new flag MD_STILL_CLOSED. Set it before calling sync_blockdev(), clear it if anyone does open the file, and abort the STOP_ARRAY attempt if it gets set before we lock against further opens. It is still possible to get problems if you open /dev/mdX, write to it, then issue the STOP_ARRAY ioctl. Just don't do that. Signed-off-by: NeilBrown --- drivers/md/md.c | 39 ++++++++++++++++++++++++++++++--------- drivers/md/md.h | 3 +++ 2 files changed, 33 insertions(+), 9 deletions(-) (limited to 'drivers') diff --git a/drivers/md/md.c b/drivers/md/md.c index 084a6540a4b..adf4d7e1d5e 100644 --- a/drivers/md/md.c +++ b/drivers/md/md.c @@ -5337,8 +5337,14 @@ static int md_set_readonly(struct mddev *mddev, struct block_device *bdev) err = -EBUSY; goto out; } - if (bdev) - sync_blockdev(bdev); + if (bdev && !test_bit(MD_STILL_CLOSED, &mddev->flags)) { + /* Someone opened the device since we flushed it + * so page cache could be dirty and it is too late + * to flush. So abort + */ + mutex_unlock(&mddev->open_mutex); + return -EBUSY; + } if (mddev->pers) { __md_stop_writes(mddev); @@ -5373,14 +5379,14 @@ static int do_md_stop(struct mddev * mddev, int mode, mutex_unlock(&mddev->open_mutex); return -EBUSY; } - if (bdev) - /* It is possible IO was issued on some other - * open file which was closed before we took ->open_mutex. - * As that was not the last close __blkdev_put will not - * have called sync_blockdev, so we must. + if (bdev && !test_bit(MD_STILL_CLOSED, &mddev->flags)) { + /* Someone opened the device since we flushed it + * so page cache could be dirty and it is too late + * to flush. So abort */ - sync_blockdev(bdev); - + mutex_unlock(&mddev->open_mutex); + return -EBUSY; + } if (mddev->pers) { if (mddev->ro) set_disk_ro(disk, 0); @@ -6417,6 +6423,20 @@ static int md_ioctl(struct block_device *bdev, fmode_t mode, !test_bit(MD_RECOVERY_NEEDED, &mddev->flags), msecs_to_jiffies(5000)); + if (cmd == STOP_ARRAY || cmd == STOP_ARRAY_RO) { + /* Need to flush page cache, and ensure no-one else opens + * and writes + */ + mutex_lock(&mddev->open_mutex); + if (atomic_read(&mddev->openers) > 1) { + mutex_unlock(&mddev->open_mutex); + err = -EBUSY; + goto abort; + } + set_bit(MD_STILL_CLOSED, &mddev->flags); + mutex_unlock(&mddev->open_mutex); + sync_blockdev(bdev); + } err = mddev_lock(mddev); if (err) { printk(KERN_INFO @@ -6670,6 +6690,7 @@ static int md_open(struct block_device *bdev, fmode_t mode) err = 0; atomic_inc(&mddev->openers); + clear_bit(MD_STILL_CLOSED, &mddev->flags); mutex_unlock(&mddev->open_mutex); check_disk_change(bdev); diff --git a/drivers/md/md.h b/drivers/md/md.h index 53283beda21..608050c43f1 100644 --- a/drivers/md/md.h +++ b/drivers/md/md.h @@ -211,6 +211,9 @@ struct mddev { #define MD_CHANGE_PENDING 2 /* switch from 'clean' to 'active' in progress */ #define MD_UPDATE_SB_FLAGS (1 | 2 | 4) /* If these are set, md_update_sb needed */ #define MD_ARRAY_FIRST_USE 3 /* First use of array, needs initialization */ +#define MD_STILL_CLOSED 4 /* If set, then array has not been opened since + * md_ioctl checked on it. + */ int suspended; atomic_t active_io; -- cgit v1.2.3-70-g09d2