3.12-stable review patch. If anyone has any objections, please let me know. ------------------ From: Dan Williams <dan.j.williams@xxxxxxxxx> commit 77873803363c9e831fc1d1e6895c084279090c22 upstream. net_dma can cause data to be copied to a stale mapping if a copy-on-write fault occurs during dma. The application sees missing data. The following trace is triggered by modifying the kernel to WARN if it ever triggers copy-on-write on a page that is undergoing dma: WARNING: CPU: 24 PID: 2529 at lib/dma-debug.c:485 debug_dma_assert_idle+0xd2/0x120() ioatdma 0000:00:04.0: DMA-API: cpu touching an active dma mapped page [pfn=0x16bcd9] Modules linked in: iTCO_wdt iTCO_vendor_support ioatdma lpc_ich pcspkr dca CPU: 24 PID: 2529 Comm: linbug Tainted: G W 3.13.0-rc1+ #353 00000000000001e5 ffff88016f45f688 ffffffff81751041 ffff88017ab0ef70 ffff88016f45f6d8 ffff88016f45f6c8 ffffffff8104ed9c ffffffff810f3646 ffff8801768f4840 0000000000000282 ffff88016f6cca10 00007fa2bb699349 Call Trace: [<ffffffff81751041>] dump_stack+0x46/0x58 [<ffffffff8104ed9c>] warn_slowpath_common+0x8c/0xc0 [<ffffffff810f3646>] ? ftrace_pid_func+0x26/0x30 [<ffffffff8104ee86>] warn_slowpath_fmt+0x46/0x50 [<ffffffff8139c062>] debug_dma_assert_idle+0xd2/0x120 [<ffffffff81154a40>] do_wp_page+0xd0/0x790 [<ffffffff811582ac>] handle_mm_fault+0x51c/0xde0 [<ffffffff813830b9>] ? copy_user_enhanced_fast_string+0x9/0x20 [<ffffffff8175fc2c>] __do_page_fault+0x19c/0x530 [<ffffffff8175c196>] ? _raw_spin_lock_bh+0x16/0x40 [<ffffffff810f3539>] ? trace_clock_local+0x9/0x10 [<ffffffff810fa1f4>] ? rb_reserve_next_event+0x64/0x310 [<ffffffffa0014c00>] ? ioat2_dma_prep_memcpy_lock+0x60/0x130 [ioatdma] [<ffffffff8175ffce>] do_page_fault+0xe/0x10 [<ffffffff8175c862>] page_fault+0x22/0x30 [<ffffffff81643991>] ? __kfree_skb+0x51/0xd0 [<ffffffff813830b9>] ? copy_user_enhanced_fast_string+0x9/0x20 [<ffffffff81388ea2>] ? memcpy_toiovec+0x52/0xa0 [<ffffffff8164770f>] skb_copy_datagram_iovec+0x5f/0x2a0 [<ffffffff8169d0f4>] tcp_rcv_established+0x674/0x7f0 [<ffffffff816a68c5>] tcp_v4_do_rcv+0x2e5/0x4a0 [..] ---[ end trace e30e3b01191b7617 ]--- Mapped at: [<ffffffff8139c169>] debug_dma_map_page+0xb9/0x160 [<ffffffff8142bf47>] dma_async_memcpy_pg_to_pg+0x127/0x210 [<ffffffff8142cce9>] dma_memcpy_pg_to_iovec+0x119/0x1f0 [<ffffffff81669d3c>] dma_skb_copy_datagram_iovec+0x11c/0x2b0 [<ffffffff8169d1ca>] tcp_rcv_established+0x74a/0x7f0: ...the problem is that the receive path falls back to cpu-copy in several locations and this trace is just one of the areas. A few options were considered to fix this: 1/ sync all dma whenever a cpu copy branch is taken 2/ modify the page fault handler to hold off while dma is in-flight Option 1 adds yet more cpu overhead to an "offload" that struggles to compete with cpu-copy. Option 2 adds checks for behavior that is already documented as broken when using get_user_pages(). At a minimum a debug mode is warranted to catch and flag these violations of the dma-api vs get_user_pages(). Thanks to David for his reproducer. Cc: Dave Jiang <dave.jiang@xxxxxxxxx> Cc: Vinod Koul <vinod.koul@xxxxxxxxx> Cc: Alexander Duyck <alexander.h.duyck@xxxxxxxxx> Reported-by: David Whipple <whipple@xxxxxxxxxxxxxxxxxxxxxxxx> Acked-by: David S. Miller <davem@xxxxxxxxxxxxx> Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- drivers/dma/Kconfig | 1 + 1 file changed, 1 insertion(+) --- a/drivers/dma/Kconfig +++ b/drivers/dma/Kconfig @@ -339,6 +339,7 @@ config NET_DMA bool "Network: TCP receive copy offload" depends on DMA_ENGINE && NET default (INTEL_IOATDMA || FSL_DMA) + depends on BROKEN help This enables the use of DMA engines in the network stack to offload receive copy-to-user operations, freeing CPU cycles. -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html