Hi Sergei,
Thank you for your patch!
On Sun, 25 Oct 2015 07:42:33 +0900,
Sergei Shtylyov wrote:
>
> In a low memory situation the following kernel oops occurs:
>
> Unable to handle kernel NULL pointer dereference at virtual address 00000050
> pgd = 8490c000
> [00000050] *pgd=4651e831, *pte=00000000, *ppte=00000000
> Internal error: Oops: 17 [#1] PREEMPT ARM
> Modules linked in:
> CPU: 0 Not tainted (3.4-at16 #9)
> PC is at skb_put+0x10/0x98
> LR is at sh_eth_poll+0x2c8/0xa10
> pc : [<8035f780>] lr : [<8028bf50>] psr: 60000113
> sp : 84eb1a90 ip : 84eb1ac8 fp : 84eb1ac4
> r10: 0000003f r9 : 000005ea r8 : 00000000
> r7 : 00000000 r6 : 940453b0 r5 : 00030000 r4 : 9381b180
> r3 : 00000000 r2 : 00000000 r1 : 000005ea r0 : 00000000
> Flags: nZCv IRQs on FIQs on Mode SVC_32 ISA ARM Segment user
> Control: 10c53c7d Table: 4248c059 DAC: 00000015
> Process klogd (pid: 2046, stack limit = 0x84eb02e8)
> [...]
>
> This is because netdev_alloc_skb() fails and 'mdp->rx_skbuff[entry]' is left
> NULL but sh_eth_rx() later uses it without checking. Add such check...
>
> Reported-by: Yasushi SHOJI <ya...@atmark-techno.com>
> Signed-off-by: Sergei Shtylyov <sergei.shtyl...@cogentembedded.com>
>
> ---
> This patch is against DaveM's 'net.git' repo.
>
> drivers/net/ethernet/renesas/sh_eth.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> Index: net/drivers/net/ethernet/renesas/sh_eth.c
> ===================================================================
> --- net.orig/drivers/net/ethernet/renesas/sh_eth.c
> +++ net/drivers/net/ethernet/renesas/sh_eth.c
> @@ -1481,6 +1481,7 @@ static int sh_eth_rx(struct net_device *
> if (mdp->cd->shift_rd0)
> desc_status >>= 16;
>
> + skb = mdp->rx_skbuff[entry];
> if (desc_status & (RD_RFS1 | RD_RFS2 | RD_RFS3 | RD_RFS4 |
> RD_RFS5 | RD_RFS6 | RD_RFS10)) {
> ndev->stats.rx_errors++;
> @@ -1496,12 +1497,11 @@ static int sh_eth_rx(struct net_device *
> ndev->stats.rx_missed_errors++;
> if (desc_status & RD_RFS10)
> ndev->stats.rx_over_errors++;
> - } else {
> + } else if (skb) {
> if (!mdp->cd->hw_swap)
> sh_eth_soft_swap(
> phys_to_virt(ALIGN(rxdesc->addr, 4)),
> pkt_len + 2);
> - skb = mdp->rx_skbuff[entry];
> mdp->rx_skbuff[entry] = NULL;
> if (mdp->cd->rpadir)
> skb_reserve(skb, NET_IP_ALIGN);
>
This certainly prevents from a bad access, however, some odd thing is
going on. Once I hit a low memory situation with this patch, network
thorough-put and response is very bad.
telnet, ping, wget takes loong time.
PING 172.16.2.13 (172.16.2.13) 56(84) bytes of data.
64 bytes from 172.16.2.13: icmp_seq=5 ttl=64 time=0.223 ms
64 bytes from 172.16.2.13: icmp_seq=6 ttl=64 time=0.195 ms
64 bytes from 172.16.2.13: icmp_seq=7 ttl=64 time=0.203 ms
64 bytes from 172.16.2.13: icmp_seq=8 ttl=64 time=0.219 ms
64 bytes from 172.16.2.13: icmp_seq=9 ttl=64 time=0.165 ms
64 bytes from 172.16.2.13: icmp_seq=10 ttl=64 time=0.171 ms
64 bytes from 172.16.2.13: icmp_seq=1 ttl=64 time=9023 ms
64 bytes from 172.16.2.13: icmp_seq=2 ttl=64 time=8022 ms
64 bytes from 172.16.2.13: icmp_seq=3 ttl=64 time=7014 ms
64 bytes from 172.16.2.13: icmp_seq=4 ttl=64 time=6006 ms
I'll investigate it.
--
yashi
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