From: Jeff Dike It is theoretically possible for a request to finish and be freed between writing it to the I/O thread and updating the sector count. In this case, the update will dereference a freed pointer. To avoid this, I delay the update until processing the next sg segment, when the request pointer is known to be good. Signed-off-by: Jeff Dike Signed-off-by: Andrew Morton --- arch/um/drivers/ubd_kern.c | 6 ++++-- 1 files changed, 4 insertions(+), 2 deletions(-) diff -puN arch/um/drivers/ubd_kern.c~uml-fix-request-sector-update arch/um/drivers/ubd_kern.c --- a/arch/um/drivers/ubd_kern.c~uml-fix-request-sector-update +++ a/arch/um/drivers/ubd_kern.c @@ -1082,7 +1082,7 @@ static void do_ubd_request(request_queue { struct io_thread_req *io_req; struct request *req; - int n; + int n, last_sectors; while(1){ struct ubd *dev = q->queuedata; @@ -1098,9 +1098,11 @@ static void do_ubd_request(request_queue } req = dev->request; + last_sectors = 0; while(dev->start_sg < dev->end_sg){ struct scatterlist *sg = &dev->sg[dev->start_sg]; + req->sector += last_sectors; io_req = kmalloc(sizeof(struct io_thread_req), GFP_ATOMIC); if(io_req == NULL){ @@ -1112,6 +1114,7 @@ static void do_ubd_request(request_queue (unsigned long long) req->sector << 9, sg->offset, sg->length, sg->page); + last_sectors = sg->length >> 9; n = os_write_file(thread_fd, &io_req, sizeof(struct io_thread_req *)); if(n != sizeof(struct io_thread_req *)){ @@ -1123,7 +1126,6 @@ static void do_ubd_request(request_queue return; } - req->sector += sg->length >> 9; dev->start_sg++; } dev->end_sg = 0; _