Messages in this thread | | | Subject | Re: [PATCH] staging: kpc2000: kpc_dma: Convert get_user_pages() --> pin_user_pages() | From | John Hubbard <> | Date | Sun, 31 May 2020 18:44:59 -0700 |
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On 2020-05-31 10:51, Souptick Joarder wrote: > In 2019, we introduced pin_user_pages*() and now we are converting > get_user_pages*() to the new API as appropriate. [1] & [2] could > be referred for more information. > > When pin_user_pages() returns numbers of partially mapped pages, > those pages were not unpinned as part of error handling. Fixed > it as part of this patch. >
Hi Souptick,
btw, Bharath (+cc) attempted to do the "put" side of this, last year. That got as far as a v4 patch [1], and then I asked him to let me put it into my tree. But then it didn't directly apply anymore after the whole design moved to pin+unpin, and so here we are now.
If Bharath is still doing kernel work, you might offer him a Co-Developed-by: tag (see https://www.kernel.org/doc/html/v4.17/process/submitting-patches.html).
Anyway, I'd recommend splitting the bug fix(es) into it at least one separate patch. That's a "best practice", and I don't see any reason not to do it here, even though the bugs are not huge.
Also I think there may be more than one bug to fix, because I just noticed that the pre-existing code is doing set_page_dirty(), when it should be doing set_page_dirty_lock(). See below.
> [1] Documentation/core-api/pin_user_pages.rst > > [2] "Explicit pinning of user-space pages": > https://lwn.net/Articles/807108/ > > Signed-off-by: Souptick Joarder <jrdr.linux@gmail.com> > Cc: John Hubbard <jhubbard@nvidia.com> > --- > Hi, > > I'm compile tested this, but unable to run-time test, so any testing > help is much appriciated. > > drivers/staging/kpc2000/kpc_dma/fileops.c | 15 ++++++++------- > 1 file changed, 8 insertions(+), 7 deletions(-) > > diff --git a/drivers/staging/kpc2000/kpc_dma/fileops.c b/drivers/staging/kpc2000/kpc_dma/fileops.c > index 8975346..29bab13 100644 > --- a/drivers/staging/kpc2000/kpc_dma/fileops.c > +++ b/drivers/staging/kpc2000/kpc_dma/fileops.c > @@ -48,6 +48,7 @@ static int kpc_dma_transfer(struct dev_private_data *priv, > u64 card_addr; > u64 dma_addr; > u64 user_ctl; > + int nr_pages = 0;
Probably best to correct the "rv" type as well: it should be an int, rather than a long.
> > ldev = priv->ldev; > > @@ -76,13 +77,15 @@ static int kpc_dma_transfer(struct dev_private_data *priv, > > // Lock the user buffer pages in memory, and hold on to the page pointers (for the sglist) > mmap_read_lock(current->mm); /* get memory map semaphore */ > - rv = get_user_pages(iov_base, acd->page_count, FOLL_TOUCH | FOLL_WRITE | FOLL_GET, acd->user_pages, NULL); > + rv = pin_user_pages(iov_base, acd->page_count, FOLL_TOUCH | FOLL_WRITE, acd->user_pages, NULL); > mmap_read_unlock(current->mm); /* release the semaphore */ > if (rv != acd->page_count) { > - dev_err(&priv->ldev->pldev->dev, "Couldn't get_user_pages (%ld)\n", rv); > + dev_err(&priv->ldev->pldev->dev, "Couldn't pin_user_pages (%ld)\n", rv); > + nr_pages = rv; > goto err_get_user_pages; > } > > + nr_pages = acd->page_count; > // Allocate and setup the sg_table (scatterlist entries) > rv = sg_alloc_table_from_pages(&acd->sgt, acd->user_pages, acd->page_count, iov_base & (PAGE_SIZE - 1), iov_len, GFP_KERNEL); > if (rv) { > @@ -189,10 +192,9 @@ static int kpc_dma_transfer(struct dev_private_data *priv, > sg_free_table(&acd->sgt); > err_dma_map_sg: > err_alloc_sg_table:
So now we end up with two unnecessary labels. Probably best to delete two of these three and name the remaining one appropriately:
err_dma_map_sg: err_alloc_sg_table: err_get_user_pages:
> - for (i = 0 ; i < acd->page_count ; i++) > - put_page(acd->user_pages[i]); > - > err_get_user_pages: > + if (nr_pages > 0) > + unpin_user_pages(acd->user_pages, nr_pages); > kfree(acd->user_pages); > err_alloc_userpages: > kfree(acd); > @@ -217,8 +219,7 @@ void transfer_complete_cb(struct aio_cb_data *acd, size_t xfr_count, u32 flags) >
There is code up here (not shown in this diff), that does a set_page_dirty(). First of all, that should be set_page_dirty_lock(), and second, maybe (or maybe not) it can all be done after the dma_unmap_sg(), at the same time as the unpin, via unpin_user_pages_dirty_lock(). In fact, it's misleading at best to leave those pages mapped, because there is an interval in there after set_page_dirty() and before put_page(), in which the device could be running and setting pages dirty. (Remember that writeback attempts can be happening concurrently with all of this, and writeback is deeply involved with page dirtiness.)
I remember Bharath wrestled with this in an earlier conversion attempt (back when we were only converting the "put_page" side of things), let me see if I can dig up that email thread for some guidance...OK, in [1] it appears that everyone finally settled on keeping the PageReserved check, but OK to move everything below the dma_unmap_sg() call.
[1] https://lore.kernel.org/r/20190720173214.GA4250@bharath12345-Inspiron-5559
> dma_unmap_sg(&acd->ldev->pldev->dev, acd->sgt.sgl, acd->sgt.nents, acd->ldev->dir); > > - for (i = 0 ; i < acd->page_count ; i++) > - put_page(acd->user_pages[i]); > + unpin_user_pages(acd->user_pages, acd->page_count); > > sg_free_table(&acd->sgt); > >
thanks, -- John Hubbard NVIDIA
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