W dniu 2017-09-20 o 20:36, Cong Wang pisze:
On Wed, Sep 20, 2017 at 11:30 AM, Eric Dumazet
<eric.duma...@gmail.com> wrote:
On Wed, 2017-09-20 at 11:22 -0700, Cong Wang wrote:
but dmesg at this time shows nothing about interfaces or flaps.
This is very odd.
We only free netdevice in free_netdev() and it is only called when
we unregister a netdevice. Otherwise pcpu_refcnt is impossible
to be NULL.
If there is a missing dev_hold() or one dev_put() in excess,
this would allow the netdev to be freed too soon.
-> Use after free.
memory holding netdev could be reallocated-cleared by some other
kernel
user.
Sure, but only unregister could trigger a free. If there is no
unregister,
like what Pawel claims, then there is no free, the refcnt just goes to
0 but the memory is still there.
About possible mistake from my side with bisect - i can judge too
early that some bisect was good
the road was:
git bisect start
# bad: [ac7b75966c9c86426b55fe1c50ae148aa4571075] Merge tag
'pinctrl-v4.13-1' of
git://git.kernel.org/pub/scm/linux/kernel/git/linusw/linux-pinctrl
git bisect bad ac7b75966c9c86426b55fe1c50ae148aa4571075
# good: [e24dd9ee5399747b71c1d982a484fc7601795f31] Merge branch
'next' of
git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/linux-security
git bisect good e24dd9ee5399747b71c1d982a484fc7601795f31
# bad: [9cc9a5cb176ccb4f2cda5ac34da5a659926f125f] datapath: Avoid
using stack larger than 1024.
git bisect bad 9cc9a5cb176ccb4f2cda5ac34da5a659926f125f
# good: [073cf9e20c333ab29744717a23f9e43ec7512a20] Merge branch
'udp-reduce-cache-pressure'
git bisect good 073cf9e20c333ab29744717a23f9e43ec7512a20
# bad: [8abd5599a520e9f188a750f1bde9dde5fb856230] Merge branch
's390-net-updates-part-2'
git bisect bad 8abd5599a520e9f188a750f1bde9dde5fb856230
# good: [2fae5d0e647c6470d206e72b5fc24972bb900f70] Merge branch
'bpf-ctx-narrow'
git bisect good 2fae5d0e647c6470d206e72b5fc24972bb900f70
# good: [41500c3e2a19ffcf40a7158fce1774de08e26ba2] rds: tcp: remove
cp_outgoing
git bisect good 41500c3e2a19ffcf40a7158fce1774de08e26ba2
# bad: [8917a777be3ba566377be05117f71b93a5fd909d] tcp: md5: add
TCP_MD5SIG_EXT socket option to set a key address prefix
git bisect bad 8917a777be3ba566377be05117f71b93a5fd909d
# good: [4a6ce2b6f2ecabbddcfe47e7cf61dd0f00b10e36] net: introduce a
new function dst_dev_put()
And currently have this running for about 4 hours without problems.
git bisect good 4a6ce2b6f2ecabbddcfe47e7cf61dd0f00b10e36
# bad: [a4c2fd7f78915a0d7c5275e7612e7793157a01f2] net: remove
DST_NOCACHE flag
Here for sure - panic
git bisect bad a4c2fd7f78915a0d7c5275e7612e7793157a01f2
# bad: [ad65a2f05695aced349e308193c6e2a6b1d87112] ipv6: call
dst_hold_safe() properly
git bisect bad ad65a2f05695aced349e308193c6e2a6b1d87112
# good: [9df16efadd2a8a82731dc76ff656c771e261827f] ipv4: call
dst_hold_safe() properly
git bisect good 9df16efadd2a8a82731dc76ff656c771e261827f
# bad: [1cfb71eeb12047bcdbd3e6730ffed66e810a0855] ipv6: take
dst->__refcnt for insertion into fib6 tree
im not 100% sure tor last two
Will test them again starting from
[95c47f9cf5e028d1ae77dc6c767c1edc8a18025b] ipv4: call dst_dev_put()
properly
git bisect bad 1cfb71eeb12047bcdbd3e6730ffed66e810a0855
# bad: [b838d5e1c5b6e57b10ec8af2268824041e3ea911] ipv4: mark
DST_NOGC and remove the operation of dst_free()
git bisect bad b838d5e1c5b6e57b10ec8af2268824041e3ea911
# first bad commit: [b838d5e1c5b6e57b10ec8af2268824041e3ea911] ipv4:
mark DST_NOGC and remove the operation of dst_free()
