The following commit has been merged in the linux branch: commit 03cadd36d51c737d7ad6aa21e2524296be6fe57f Author: Michael Holzheu holzheu@linux.vnet.ibm.com Date: Wed Oct 14 12:43:45 2009 +0200

[S390] tape390: Fix request queue handling in block driver

When setting a channel attached tape online under Linux 2.6.31, the

"vol_id" process from udev hangs in sync_page(): 2 sync_page+144 [0x1dfaac] 3 __wait_on_bit_lock+194 [0x58c23e] 4 __lock_page+116 [0x1df9dc] 5 truncate_inode_pages_range+728 [0x1ed7cc] 6 __blkdev_put+244 [0x25f738] 7 __fput+300 [0x229c4c] 8 filp_close+122 [0x225a3a]

The reason for that is an error in the request queue handling. It can happen that we fetch a request, but do not process it further because the number of queued requests exceeds TAPEBLOCK_MIN_REQUEUE. To fix this, we should call blk_peek_request() instead of blk_fetch_request() in the while condition and fetch the request in the loop body afterwards.

This bug was introduced with the patch "block: implement and enforce request peek/start/fetch" (9934c8c04561413609d2bc38c6b9f268cba774a4)

Signed-off-by: Michael Holzheu holzheu@linux.vnet.ibm.com Signed-off-by: Martin Schwidefsky schwidefsky@de.ibm.com

diff --git a/drivers/s390/char/tape_block.c b/drivers/s390/char/tape_block.c index 64f57ef..0c0705b 100644 --- a/drivers/s390/char/tape_block.c +++ b/drivers/s390/char/tape_block.c @@ -162,9 +162,10 @@ tapeblock_requeue(struct work_struct *work) { spin_lock_irq(&device->blk_data.request_queue_lock); while ( !blk_queue_plugged(queue) && - (req = blk_fetch_request(queue)) && + blk_peek_request(queue) && nr_queued < TAPEBLOCK_MIN_REQUEUE ) { + req = blk_fetch_request(queue); if (rq_data_dir(req) == WRITE) { DBF_EVENT(1, "TBLOCK: Rejecting write request\n"); spin_unlock_irq(&device->blk_data.request_queue_lock);