Summary: with CONFIG_HIGHMEM set, net/ipv4/udp.c::udp_poll()
fails when rx'ing an skb with fragments.
Present in [at least] 2.6.11.*, 2.6.10
Details:
User space code polling on a blocking socket fd receives an
skb with fragments -- this is very unlikely in the common
case but can happen with encapsulation etc; however its pretty
much guaranteed to happen under Xen 2.x when communicating
between dom0 and domU.
Example backtrace from console:
kernel: Badness in local_bh_enable at kernel/softirq.c:140
kernel: [local_bh_enable+130/144] local_bh_enable+0x82/0x90
kernel: [skb_checksum+317/704] skb_checksum+0x13d/0x2c0
kernel: [udp_poll+154/352] udp_poll+0x9a/0x160
kernel: [sock_poll+41/64] sock_poll+0x29/0x40
kernel: [do_pollfd+149/160] do_pollfd+0x95/0xa0
kernel: [do_poll+106/208] do_poll+0x6a/0xd0
kernel: [sys_poll+353/576] sys_poll+0x161/0x240
kernel: [sys_gettimeofday+60/144] sys_gettimeofday+0x3c/0x90
kernel: [__pollwait+0/208] __pollwait+0x0/0xd0
kernel: [syscall_call+7/11] syscall_call+0x7/0xb
Reconstructed forward trace:
net/ipv4/udp.c:1334 spin_lock_irq()
net/ipv4/udp.c:1336 udp_checksum_complete()
net/core/skbuff.c:1069 skb_shinfo(skb)->nr_frags > 1
net/core/skbuff.c:1086 kunmap_skb_frag()
net/core/skbuff.h:1087 local_bh_enable()
kernel/softirq.c:0140 WARN_ON(irqs_disabled());
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