>-----Original Message----- >From: Anton Vorontsov [mailto:avoront...@ru.mvista.com] >Sent: Saturday, February 27, 2010 3:08 AM >To: Paul Gortmaker >Cc: Martyn Welch; net...@vger.kernel.org; >linux-ker...@vger.kernel.org; linuxppc-dev list; Kumar >Gopalpet-B05799; da...@davemloft.net >Subject: Re: Gianfar driver failing on MPC8641D based board > >On Fri, Feb 26, 2010 at 11:27:42AM -0500, Paul Gortmaker wrote: >> On 10-02-26 11:10 AM, Anton Vorontsov wrote: >> > On Fri, Feb 26, 2010 at 03:34:07PM +0000, Martyn Welch wrote: >> > [...] >> >> Out of 10 boot attempts, 7 failed. >> > >> > OK, I see why. With ip=on (dhcp boot) it's much harder to trigger >> > it. With static ip config can I see the same. >> >> I'd kind of expected to see us stuck in gianfar on that >lock, but the >> SysRQ-T doesn't show us hung up anywhere in gianfar itself. >> [This was on a base 2.6.33, with just a small sysrq fix patch] > >> [df841a30] [c0009fc4] __switch_to+0x8c/0xf8 > >> [df841a50] [c0350160] schedule+0x354/0x92c > >> [df841ae0] [c0331394] rpc_wait_bit_killable+0x2c/0x54 > >> [df841af0] [c0350eb0] __wait_on_bit+0x9c/0x108 > >> [df841b10] [c0350fc0] out_of_line_wait_on_bit+0xa4/0xb4 > >> [df841b40] [c0331cf0] __rpc_execute+0x16c/0x398 > >> [df841b90] [c0329abc] rpc_run_task+0x48/0x9c > >> [df841ba0] [c0329c40] rpc_call_sync+0x54/0x88 > >> [df841bd0] [c015e780] nfs_proc_lookup+0x94/0xe8 > >> [df841c20] [c014eb60] nfs_lookup+0x12c/0x230 > >> [df841d50] [c00b9680] do_lookup+0x118/0x288 > >> [df841d80] [c00bb904] link_path_walk+0x194/0x1118 > >> [df841df0] [c00bcb08] path_walk+0x8c/0x168 > >> [df841e20] [c00bcd6c] do_path_lookup+0x74/0x7c > >> [df841e40] [c00be148] do_filp_open+0x5d4/0xba4 > >> [df841f10] [c00abe94] do_sys_open+0xac/0x190 > > >Yeah, I don't think this is gianfar-related. It must be >something else triggered by the fact that gianfar no longer >sends stuff. > >OK, I think I found what's happening in gianfar. > >Some background... > >start_xmit() prepares new skb for transmitting, generally it >does three things: > >1. sets up all BDs (marks them ready to send), except the first one. >2. stores skb into tx_queue->tx_skbuff so that clean_tx_ring() > would cleanup it later. >3. sets up the first BD, i.e. marks it ready. > >Here is what clean_tx_ring() does: > >1. reads skbs from tx_queue->tx_skbuff >2. Checks if the *last* BD is ready. If it's still ready [to send] > then it it isn't transmitted, so clean_tx_ring() returns. > Otherwise it actually cleanups BDs. All is OK. > >Now, if there is just one BD, code flow: > >- start_xmit(): stores skb into tx_skbuff. Note that the first BD > (which is also the last one) isn't marked as ready, yet. >- clean_tx_ring(): sees that skb is not null, *and* its lstatus > says that it is NOT ready (like if BD was sent), so it cleans > it up (bad!) >- start_xmit(): marks BD as ready [to send], but it's too late. > >We can fix this simply by reordering lstatus/tx_skbuff writes. > >It works flawlessly on my p2020, please try it.
Anton, Understood, and thanks for the explanation. Am I correct in saying that this is due to the out-of-order execution capability on powerpc ? I have one more question, why don't we use use atomic_t for num_txbdfree and completely do away with spin_locks in gfar_clean_tx_ring() and gfar_start_xmit(). In an non-SMP, scenario I would feel there is absolutely no requirement of spin_locks and in case of SMP atomic operation would be much more safer on powerpc rather than spin_locks. What is your suggestion ? -- Thanks Sandeep > >Thanks! > > >diff --git a/drivers/net/gianfar.c b/drivers/net/gianfar.c >index 8bd3c9f..cccb409 100644 >--- a/drivers/net/gianfar.c >+++ b/drivers/net/gianfar.c >@@ -2021,7 +2021,6 @@ static int gfar_start_xmit(struct >sk_buff *skb, struct net_device *dev) > } > > /* setup the TxBD length and buffer pointer for the first BD */ >- tx_queue->tx_skbuff[tx_queue->skb_curtx] = skb; > txbdp_start->bufPtr = dma_map_single(&priv->ofdev->dev, >skb->data, > skb_headlen(skb), DMA_TO_DEVICE); > >@@ -2053,6 +2052,10 @@ static int gfar_start_xmit(struct >sk_buff *skb, struct net_device *dev) > > txbdp_start->lstatus = lstatus; > >+ eieio(); /* force lstatus write before tx_skbuff */ >+ >+ tx_queue->tx_skbuff[tx_queue->skb_curtx] = skb; >+ > /* Update the current skb pointer to the next entry we will use > * (wrapping if necessary) */ > tx_queue->skb_curtx = (tx_queue->skb_curtx + 1) & > > _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
