mthca_map_user_db() has two problems regarding the call to get_user_pages():
(i) It is not done under mmap_sem. (ii) It is done under the db_table mutex, which protects all database related operations. Should any of these be called under mmap_sem, we get an ABBA deadlock. In addition, gup can be performance intensive, which could contend other mapping/ unmapping ops. To fix this, we can drop the mutex while doing a gup_fast(), once done, recheck to see the page was mapped while we didn't hold the mutex, and exit out with the corresponding housekeeping. Suggested-by: Al Viro <[email protected]> Signed-off-by: Davidlohr Bueso <[email protected]> --- - Compile tested only. - Should I be wrong about no callers already holding mmap_sem, I still think calling gup without the mutex makes sense for improved paralellism. Now, if callers can hold the mmap_sem, it's wrong to do copy_from_user right before calling mthca_map_user_db. drivers/infiniband/hw/mthca/mthca_memfree.c | 20 +++++++++++++++++++- 1 file changed, 19 insertions(+), 1 deletion(-) diff --git a/drivers/infiniband/hw/mthca/mthca_memfree.c b/drivers/infiniband/hw/mthca/mthca_memfree.c index c6fe89d79248..046871878a02 100644 --- a/drivers/infiniband/hw/mthca/mthca_memfree.c +++ b/drivers/infiniband/hw/mthca/mthca_memfree.c @@ -472,9 +472,27 @@ int mthca_map_user_db(struct mthca_dev *dev, struct mthca_uar *uar, goto out; } - ret = get_user_pages(uaddr & PAGE_MASK, 1, FOLL_WRITE, pages, NULL); + mutex_unlock(&db_tab->mutex); + + ret = get_user_pages_fast(uaddr & PAGE_MASK, 1, FOLL_WRITE, pages); if (ret < 0) + return ret; + + mutex_lock(&db_tab->mutex); + + if (db_tab->page[i].refcount >= MTHCA_DB_REC_PER_PAGE || + (db_tab->page[i].uvirt && db_tab->page[i].uvirt != uaddr)) { + put_page(pages[0]); + ret = -EINVAL; goto out; + } + + /* page was already mapped by another task while we were doing gup */ + if (db_tab->page[i].refcount) { + put_page(pages[0]); + ++db_tab->page[i].refcount; + goto out; + } sg_set_page(&db_tab->page[i].mem, pages[0], MTHCA_ICM_PAGE_SIZE, uaddr & ~PAGE_MASK); -- 2.13.6
