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Date: Thu, 17 Sep 2020 10:34:24 -0700
From: Ira Weiny <ira.weiny@...el.com>
To: Dan Carpenter <dan.carpenter@...cle.com>
Cc: Souptick Joarder <jrdr.linux@...il.com>, jhubbard@...dia.com,
mporter@...nel.crashing.org, alex.bou9@...il.com,
akpm@...ux-foundation.org, gustavoars@...nel.org,
madhuparnabhowmik10@...il.com, linux-kernel@...r.kernel.org,
Matthew Wilcox <willy@...radead.org>
Subject: Re: [linux-next PATCH] rapidio: Fix error handling path
On Thu, Sep 17, 2020 at 03:39:51PM +0300, Dan Carpenter wrote:
> On Wed, Sep 16, 2020 at 01:02:32PM +0300, Dan Carpenter wrote:
> > On Wed, Sep 16, 2020 at 09:12:17AM +0530, Souptick Joarder wrote:
> > > There is an error when pin_user_pages_fast() returns -ERRNO and
> > > inside error handling path driver end up calling unpin_user_pages()
> > > with -ERRNO which is not correct.
> > >
> > > This patch will fix the problem.
> >
> > There are a few ways we could prevent bug in the future.
> >
> > 1) This could have been caught with existing static analysis tools
> > which warn about when a value is set but not used.
> >
> > 2) I've created a Smatch check which warngs about:
> >
> > drivers/rapidio/devices/rio_mport_cdev.c:955 rio_dma_transfer() warn: unpinning negative pages 'nr_pages'
> >
> > I'll test it out tonight and see how well it works. I don't
> > immediately see any other bugs allthough Smatch doesn't like the code
> > in siw_umem_release(). It uses "min_t(int" which suggests that
> > negative pages are okay.
> >
> > int to_free = min_t(int, PAGES_PER_CHUNK, num_pages);
> >
>
> I only found one bug but I'm going to add unpin_user_pages_dirty_lock()
> to the mix a retest. There were a few other false positives. In
> reviewing the code, I noticed that orangefs_bufmap_map() is also buggy.
>
> I sort of feel like returning partial successes is not working. We
> could easily make a wrapper which either pins everything or it returns
> an error code.
I guess the question is are there drivers which will keep working (or limp
along?) on partial pins? A quick search of a driver I thought did this does
not apparently any more... So it sounds good to me from 30,000 feet! :-D
Ira
>
> drivers/misc/mic/scif/scif_rma.c:1399 __scif_pin_pages() warn: unpinning negative pages 'pinned_pages->nr_pages'
>
> drivers/misc/mic/scif/scif_rma.c
> 1355 vmalloc_addr = true;
> 1356
> 1357 for (i = 0; i < nr_pages; i++) {
> 1358 if (vmalloc_addr)
> 1359 pinned_pages->pages[i] =
> 1360 vmalloc_to_page(addr + (i * PAGE_SIZE));
> 1361 else
> 1362 pinned_pages->pages[i] =
> 1363 virt_to_page(addr + (i * PAGE_SIZE));
> 1364 }
> 1365 pinned_pages->nr_pages = nr_pages;
> 1366 pinned_pages->map_flags = SCIF_MAP_KERNEL;
> 1367 } else {
> 1368 /*
> 1369 * SCIF supports registration caching. If a registration has
> 1370 * been requested with read only permissions, then we try
> 1371 * to pin the pages with RW permissions so that a subsequent
> 1372 * transfer with RW permission can hit the cache instead of
> 1373 * invalidating it. If the upgrade fails with RW then we
> 1374 * revert back to R permission and retry
> 1375 */
> 1376 if (prot == SCIF_PROT_READ)
> 1377 try_upgrade = true;
> 1378 prot |= SCIF_PROT_WRITE;
> 1379 retry:
> 1380 mm = current->mm;
> 1381 if (ulimit) {
> 1382 err = __scif_check_inc_pinned_vm(mm, nr_pages);
> 1383 if (err) {
> 1384 pinned_pages->nr_pages = 0;
> 1385 goto error_unmap;
> 1386 }
> 1387 }
> 1388
> 1389 pinned_pages->nr_pages = pin_user_pages_fast(
> 1390 (u64)addr,
> 1391 nr_pages,
> 1392 (prot & SCIF_PROT_WRITE) ? FOLL_WRITE : 0,
> 1393 pinned_pages->pages);
> 1394 if (nr_pages != pinned_pages->nr_pages) {
> 1395 if (try_upgrade) {
> 1396 if (ulimit)
> 1397 __scif_dec_pinned_vm_lock(mm, nr_pages);
> 1398 /* Roll back any pinned pages */
> 1399 unpin_user_pages(pinned_pages->pages,
> 1400 pinned_pages->nr_pages);
> ^^^^^^^^^^^^^^^^^^^^^^
> Negative.
>
> 1401 prot &= ~SCIF_PROT_WRITE;
> 1402 try_upgrade = false;
> 1403 goto retry;
> 1404 }
> 1405 }
> 1406 pinned_pages->map_flags = 0;
> 1407 }
> 1408
> 1409 if (pinned_pages->nr_pages < nr_pages) {
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> These are both signed so it negative ->nr_pages are less than nr_pages.
>
> 1410 err = -EFAULT;
> 1411 pinned_pages->nr_pages = nr_pages;
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> This sets it to "everything was pinned".
>
> 1412 goto dec_pinned;
> 1413 }
> 1414
> 1415 *out_prot = prot;
> 1416 atomic_set(&pinned_pages->ref_count, 1);
> 1417 *pages = pinned_pages;
> 1418 return err;
> 1419 dec_pinned:
> 1420 if (ulimit)
> 1421 __scif_dec_pinned_vm_lock(mm, nr_pages);
> 1422 /* Something went wrong! Rollback */
> 1423 error_unmap:
> 1424 pinned_pages->nr_pages = nr_pages;
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> This assumes everything was pinned successfully.
>
> 1425 scif_destroy_pinned_pages(pinned_pages);
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> We absolutely don't want to pass negative ->nr_pages to this function
> either.
>
> 1426 *pages = NULL;
> 1427 dev_dbg(scif_info.mdev.this_device,
> 1428 "%s %d err %d len 0x%lx\n", __func__, __LINE__, err, len);
> 1429 return err;
> 1430 }
>
> regards,
> dan carpenter
>
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