dmaengine: hisilicon: Add multi-thread support for a DMA channel

In the Linux kernel, the following vulnerability has been resolved: dmaengine: hisilicon: Add multi-thread support for a DMA channel When we get a DMA channel and try to use it in multiple threads it will cause oops and hanging the system. % echo 100 > /sys/module/dmatest/parameters/threads_per_chan % echo 100 > /sys/module/dmatest/parameters/iterations % echo 1 > /sys/module/dmatest/parameters/run [383493.327077] Unable to handle kernel paging request at virtual address dead000000000108 [383493.335103] Mem abort info: [383493.335103] ESR = 0x96000044 [383493.335105] EC = 0x25: DABT (current EL), IL = 32 bits [383493.335107] SET = 0, FnV = 0 [383493.335108] EA = 0, S1PTW = 0 [383493.335109] FSC = 0x04: level 0 translation fault [383493.335110] Data abort info: [383493.335111] ISV = 0, ISS = 0x00000044 [383493.364739] CM = 0, WnR = 1 [383493.367793] [dead000000000108] address between user and kernel address ranges [383493.375021] Internal error: Oops: 96000044 [#1] PREEMPT SMP [383493.437574] CPU: 63 PID: 27895 Comm: dma0chan0-copy2 Kdump: loaded Tainted: GO 5.17.0-rc4+ #2 [383493.457851] pstate: 204000c9 (nzCv daIF +PAN -UAO -TCO -DIT -SSBS BTYPE=--) [383493.465331] pc : vchan_tx_submit+0x64/0xa0 [383493.469957] lr : vchan_tx_submit+0x34/0xa0 This occurs because the transmission timed out, and that's due to data race. Each thread rewrite channels's descriptor as soon as device_issue_pending is called. It leads to the situation that the driver thinks that it uses the right descriptor in interrupt handler while channels's descriptor has been changed by other thread. The descriptor which in fact reported interrupt will not be handled any more, as well as its tx->callback. That's why timeout reports. With current fixes channels' descriptor changes it's value only when it has been used. A new descriptor is acquired from vc->desc_issued queue that is already filled with descriptors that are ready to be sent. Threads have no direct access to DMA channel descriptor. In case of channel's descriptor is busy, try to submit to HW again when a descriptor is completed. In this case, vc->desc_issued may be empty when hisi_dma_start_transfer is called, so delete error reporting on this. Now it is just possible to queue a descriptor for further processing.