io_uring/rsrc: fix folio unpinning

Commit 5afb4bf upstream.

syzbot complains about an unmapping failure:

[  108.070381][   T14] kernel BUG at mm/gup.c:71!
[  108.070502][   T14] Internal error: Oops - BUG: 00000000f2000800 [#1]  SMP
[  108.123672][   T14] Hardware name: QEMU KVM Virtual Machine, BIOS edk2-20250221-8.fc42 02/21/2025
[  108.127458][   T14] Workqueue: iou_exit io_ring_exit_work
[  108.174205][   T14] Call trace:
[  108.175649][   T14]  sanity_check_pinned_pages+0x7cc/0x7d0 (P)
[  108.178138][   T14]  unpin_user_page+0x80/0x10c
[  108.180189][   T14]  io_release_ubuf+0x84/0xf8
[  108.182196][   T14]  io_free_rsrc_node+0x250/0x57c
[  108.184345][   T14]  io_rsrc_data_free+0x148/0x298
[  108.186493][   T14]  io_sqe_buffers_unregister+0x84/0xa0
[  108.188991][   T14]  io_ring_ctx_free+0x48/0x480
[  108.191057][   T14]  io_ring_exit_work+0x764/0x7d8
[  108.193207][   T14]  process_one_work+0x7e8/0x155c
[  108.195431][   T14]  worker_thread+0x958/0xed8
[  108.197561][   T14]  kthread+0x5fc/0x75c
[  108.199362][   T14]  ret_from_fork+0x10/0x20

We can pin a tail page of a folio, but then io_uring will try to unpin
the head page of the folio. While it should be fine in terms of keeping
the page actually alive, mm folks say it's wrong and triggers a debug
warning. Use unpin_user_folio() instead of unpin_user_page*.

Cc: [email protected]
Debugged-by: David Hildenbrand <[email protected]>
Reported-by: [email protected]
Closes: https://lkml.kernel.org/r/[email protected]
Fixes: a8edbb4 ("io_uring/rsrc: enable multi-hugepage buffer coalescing")
Signed-off-by: Pavel Begunkov <[email protected]>
Link: https://lore.kernel.org/io-uring/a28b0f87339ac2acf14a645dad1e95bbcbf18acd.1750771718.git.asml.silence@gmail.com/
[axboe: adapt to current tree, massage commit message]
Signed-off-by: Jens Axboe <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: isilence

io_uring/rsrc.c

@@ -119,8 +119,11 @@ static void io_buffer_unmap(struct io_ring_ctx *ctx, struct io_mapped_ubuf **slo
 	if (imu != &dummy_ubuf) {
 		if (!refcount_dec_and_test(&imu->refs))
 			return;
-		for (i = 0; i < imu->nr_bvecs; i++)
-			unpin_user_page(imu->bvec[i].bv_page);
+		for (i = 0; i < imu->nr_bvecs; i++) {
+			struct folio *folio = page_folio(imu->bvec[i].bv_page);
+
+			unpin_user_folio(folio, 1);
+		}
 		if (imu->acct_pages)
 			io_unaccount_mem(ctx, imu->acct_pages);
 		kvfree(imu);
@@ -1010,8 +1013,10 @@ static int io_sqe_buffer_register(struct io_ring_ctx *ctx, struct iovec *iov,
 done:
 	if (ret) {
 		kvfree(imu);
-		if (pages)
-			unpin_user_pages(pages, nr_pages);
+		if (pages) {
+			for (i = 0; i < nr_pages; i++)
+				unpin_user_folio(page_folio(pages[i]), 1);
+		}
 	}
 	kvfree(pages);
 	return ret;