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SubjectRe: [PATCH] connector: Fix regression introduced by sid connector
On Fri, 2 Oct 2009, Christian Borntraeger wrote:

> since commit 02b51df1b07b4e9ca823c89284e704cadb323cd1 (proc connector: add event
> for process becoming session leader) we have the following warning:
> Badness at kernel/softirq.c:143
> [...]
> Krnl PSW : 0404c00180000000 00000000001481d4 (local_bh_enable+0xb0/0xe0)
> [...]
> Call Trace:
> ([<000000013fe04100>] 0x13fe04100)
> [<000000000048a946>] sk_filter+0x9a/0xd0
> [<000000000049d938>] netlink_broadcast+0x2c0/0x53c
> [<00000000003ba9ae>] cn_netlink_send+0x272/0x2b0
> [<00000000003baef0>] proc_sid_connector+0xc4/0xd4
> [<0000000000142604>] __set_special_pids+0x58/0x90
> [<0000000000159938>] sys_setsid+0xb4/0xd8
> [<00000000001187fe>] sysc_noemu+0x10/0x16
> [<00000041616cb266>] 0x41616cb266
>
> The warning is
> ---> WARN_ON_ONCE(in_irq() || irqs_disabled());
>
> The network code must not be called with disabled interrupts but
> sys_setsid holds the tasklist_lock with spinlock_irq while calling
> the connector.
> After a discussion we agreed that we can move proc_sid_connector
> from __set_special_pids to sys_setsid.
> We also agreed that it is sufficient to change the check from
> task_session(curr) != pid into err > 0, since if we don't change the
> session, this means we were already the leader and return -EPERM.
>
> One last thing:
> There is also daemonize(), and some people might want to get a
> notification in that case. Since daemonize() is only needed if a user
> space does kernel_thread this does not look important (and there seems
> to be no consensus if this connector should be called in daemonize). If
> we really want this, we can add proc_sid_connector to daemonize() in an
> additional patch (Scott?)
>
> Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
> CCed: Scott James Remnant <scott@ubuntu.com>
> CCed: Matt Helsley <matthltc@us.ibm.com>
> CCed: David S. Miller <davem@davemloft.net>
> Acked-by: Oleg Nesterov <oleg@redhat.com>
> Acked-by: Evgeniy Polyakov <zbr@ioremap.net>

Acked-by: David Rientjes <rientjes@google.com>

I was getting the same softirq warnings and later in slub in slab_alloc()
at might_sleep_if(gfpflags & __GFP_WAIT) from __alloc_skb(..., GFP_KERNEL)
in this context that would infinitely spam my log.


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