On Mon, Feb 01, 2010 at 07:18:07AM +0100, Gerrit Renker wrote:
> This reverts commit (38ff3e6bb987ec583268da8eb22628293095d43b) ("dccp_probe:
> Fix module load dependencies between dccp and dccp_probe", from 15 Jan). Not
> only does it not work:
>
> % modprobe -v dccp_probe
> kernel: [ 1431.442912] sys_init_module: 'dccp_probe'->init suspiciously \
> returned 1, it should follow 0/-E convention
> kernel: [ 1431.442915] sys_init_module: loading module anyway...
>
>
> ... but it also causes a crash:
>
> % rmmod dccp_probe
> kernel: [ 1777.305846] kernel BUG at /usr/src/davem-2.6/mm/slab.c:521!
> kernel: [ 1777.305852] invalid opcode: 0000 [#1] SMP
> kernel: [ 1777.305861] last sysfs file: /sys/class/power_supply/BAT0/energy_full
> kernel: [ 1777.305867] Modules linked in: dccp_probe(-) iwl3945 iwlcore [last unloaded: dccp]
> kernel: [ 1777.305883]
> kernel: [ 1777.305891] Pid: 12912, comm: rmmod Tainted: G R 2.6.33-rc5 #6 2008URG/2008URG
> kernel: [ 1777.305899] EIP: 0060:[<c01d5e43>] EFLAGS: 00010046 CPU: 1
> kernel: [ 1777.305910] EIP is at kfree+0x73/0x150
> kernel: [ 1777.305916] EAX: c1678c00 EBX: 00000000 ECX: c01d5e15 EDX: 40080000
> kernel: [ 1777.305922] ESI: c015cb9a EDI: 080488a0 EBP: f4ffbf34 ESP: f4ffbf10
> kernel: [ 1777.305929] DS: 007b ES: 007b FS: 00d8 GS: 00e0 SS: 0068
> kernel: [ 1777.305936] Process rmmod (pid: 12912, ti=f4ffb000 task=f61e8620 task.ti=f4ffb000)
>
> ==> After reverting the commit:
>
> % modprobe -v dccp_probe
> insmod /lib/modules/2.6.33-rc5/kernel/net/dccp/dccp.ko
> insmod /lib/modules/2.6.33-rc5/kernel/net/dccp/dccp_probe.ko
>
> % lsmod
> Module Size Used by
> dccp_probe 2345 0
> dccp 120233 1 dccp_probe
>
> Previously (during about 4 years of this module's history) there had never
> been a problem with the 'silent dependency' that the commit tried to fix:
> this dependency is deliberate and required, since dccp_probe performs probing
> of dccp connections and hence needs to know about dccp internals.
>
> Signed-off-by: Gerrit Renker <gerrit@xxxxxxxxxxxxxx>
This doesn't make any sense. Gerrit, you don't understand what the patch was
trying to do. There is a silent dependency, in that this module requires the
dccp module to be loaded, but the reference to the dccp_send_probe symbol isn't
one that depmod can see. If you don't load dccp first, dccp_probe fails, why
bother to allow that when try_then_request_module can avoid it?
The problem here is the construction of the first argument,
try_then_request_module should only return valid return codes from the first
argument, and my first argument is malformed. register_jprobe returns zero on
success, so I need to check its return in the call for 0, in case we need to
trigger the request_module action, but in so doing ret gets the value of
(register_jprobe(&dccp_send_probe) == 0), which will always be 0 or 1. What we
actually need to do is assign the result of register_jprobe to ret, without the
side effect of the comparison. I've not tested it, but this should do it,
without re-breaking the silent dependency.
Signed-off-by: Neil Horman <nhorman@xxxxxxxxxxxxx>
probe.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/net/dccp/probe.c b/net/dccp/probe.c
index bace1d8..a8f5fdf 100644
--- a/net/dccp/probe.c
+++ b/net/dccp/probe.c
@@ -161,7 +161,8 @@ static __init int dccpprobe_init(void)
if (!proc_net_fops_create(&init_net, procname, S_IRUSR, &dccpprobe_fops))
goto err0;
- ret = try_then_request_module((register_jprobe(&dccp_send_probe) == 0),
+ try_then_request_module(
+ ((ret = register_jprobe(&dccp_send_probe)) == 0),
"dccp");
if (ret)
goto err1;
--
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