From: Hannes Frederic Sowa <hidden> Date: 2016-08-24 21:48:08
On 24.08.2016 16:24, Nikolay Borisov wrote:
Hello,
I hit the following BUG:
[1851513.239831] ------------[ cut here ]------------
[1851513.240079] kernel BUG at net/unix/garbage.c:149!
[1851513.240313] invalid opcode: 0000 [#1] SMP
[1851513.248320] CPU: 37 PID: 11683 Comm: nginx Tainted: G O 4.4.14-clouder3 #26
[1851513.248719] Hardware name: Supermicro X10DRi/X10DRi, BIOS 1.1 04/14/2015
[1851513.248966] task: ffff883b0f6f0000 ti: ffff880189cf0000 task.ti: ffff880189cf0000
[1851513.249361] RIP: 0010:[<ffffffff815f895d>] [<ffffffff815f895d>] unix_notinflight+0x8d/0x90
[1851513.249846] RSP: 0018:ffff880189cf3cf8 EFLAGS: 00010246
[1851513.250082] RAX: ffff883b05491968 RBX: ffff883b05491680 RCX: ffff8807f9967330
[1851513.250476] RDX: 0000000000000001 RSI: ffff882e6d8bae00 RDI: ffffffff82073f10
[1851513.250886] RBP: ffff880189cf3d08 R08: ffff880cbc70e200 R09: 0000000180200001
[1851513.251280] R10: ffff883fff3b9dc0 R11: ffffea0032f1c380 R12: ffff883fbaf50000
[1851513.251674] R13: ffffffff815f6354 R14: ffff881a7c77b140 R15: ffff881a7c7792c0
[1851513.252083] FS: 00007f4f19573720(0000) GS:ffff883fff3a0000(0000) knlGS:0000000000000000
[1851513.252481] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[1851513.252717] CR2: 00000000013062d8 CR3: 0000001712f32000 CR4: 00000000001406e0
[1851513.253116] Stack:
[1851513.253345] 00000000ffffffff ffff880189cf3d40 ffff880189cf3d28 ffffffff815f4383
[1851513.254022] ffff8839ee11a800 ffff8839ee11a800 ffff880189cf3d60 ffffffff815f53b8
[1851513.254685] 0000000000000000 ffff883406788de0 0000000000000000 0000000000000000
[1851513.255360] Call Trace:
[1851513.255594] [<ffffffff815f4383>] unix_detach_fds.isra.19+0x43/0x50
[1851513.255851] [<ffffffff815f53b8>] unix_destruct_scm+0x48/0x80
[1851513.256090] [<ffffffff815384af>] skb_release_head_state+0x4f/0xb0
[1851513.256328] [<ffffffff81538522>] skb_release_all+0x12/0x30
[1851513.256564] [<ffffffff81538592>] kfree_skb+0x32/0xa0
[1851513.256810] [<ffffffff815f6354>] unix_release_sock+0x1e4/0x2c0
[1851513.257046] [<ffffffff815f6450>] unix_release+0x20/0x30
[1851513.257284] [<ffffffff8152fbcf>] sock_release+0x1f/0x80
[1851513.257521] [<ffffffff8152fc42>] sock_close+0x12/0x20
[1851513.257769] [<ffffffff8119a8aa>] __fput+0xea/0x1f0
[1851513.258005] [<ffffffff8119a9ee>] ____fput+0xe/0x10
[1851513.258244] [<ffffffff8106fccf>] task_work_run+0x7f/0xb0
[1851513.258488] [<ffffffff81002210>] exit_to_usermode_loop+0xc0/0xd0
[1851513.258728] [<ffffffff81002a90>] syscall_return_slowpath+0x80/0xf0
[1851513.258983] [<ffffffff816147b4>] int_ret_from_sys_call+0x25/0x9f
[1851513.259222] Code: 7e 5b 41 5c 5d c3 48 8b 8b e8 02 00 00 48 8b 93 f0 02 00 00 48 89 51 08 48 89 0a 48 89 83 e8 02 00 00 48 89 83 f0 02 00 00 eb b8 <0f> 0b 90 0f 1f 44 00 00 55 48 c7 c7 10 3f 07 82 48 89 e5 41 54
[1851513.268473] RIP [<ffffffff815f895d>] unix_notinflight+0x8d/0x90
[1851513.268793] RSP <ffff880189cf3cf8>
That's essentially BUG_ON(list_empty(&u->link));
I see that all the code involving the ->link member hasn't really been
touched since it was introduced in 2007. So this must be a latent bug.
This is the first time I've observed it. The state
of the struct unix_sock can be found here http://sprunge.us/WCMW . Evidently,
there are no inflight sockets.
One commit which could have to do with that is
commit fc64869c48494a401b1fb627c9ecc4e6c1d74b0d
Author: Andrey Ryabinin [off-list ref]
Date: Wed May 18 19:19:27 2016 +0300
net: sock: move ->sk_shutdown out of bitfields.
but that is only a wild guess.
Which unix_sock did you extract specifically in the url you provided? In
unix_notinflight we are specifically checking an unix domain socket that
is itself being transferred over another af_unix domain socket and not
the unix domain socket being released at this point.
Can you reproduce this and maybe also with a newer kernel?
Thanks for the report,
Hannes
From: Nikolay Borisov <hidden> Date: 2016-08-24 23:30:16
On Thu, Aug 25, 2016 at 12:40 AM, Hannes Frederic Sowa
[off-list ref] wrote:
On 24.08.2016 16:24, Nikolay Borisov wrote:
[SNIP]
One commit which could have to do with that is
commit fc64869c48494a401b1fb627c9ecc4e6c1d74b0d
Author: Andrey Ryabinin [off-list ref]
Date: Wed May 18 19:19:27 2016 +0300
net: sock: move ->sk_shutdown out of bitfields.
but that is only a wild guess.
Which unix_sock did you extract specifically in the url you provided? In
unix_notinflight we are specifically checking an unix domain socket that
is itself being transferred over another af_unix domain socket and not
the unix domain socket being released at this point.
So this is the state of the socket that is being passed to
unix_notinflight. I have a complete crashdump so if you need more info
to diagnose it I'm happy to provide it. I'm not too familiar with the
code in question so I will need a bit of time to grasp what actually
is happening.
Can you reproduce this and maybe also with a newer kernel?
Unfortunately I cannot reproduce this since it happened on a
production server nor can I change the kernel. But clearly there is
something wrong, and given that this is a stable kernel and no
relevant changes have gone in latest stable I believe the problem
(albeit hardly reproducible) would still persist.
From: Hannes Frederic Sowa <hidden> Date: 2016-08-26 20:24:31
On 25.08.2016 01:30, Nikolay Borisov wrote:
On Thu, Aug 25, 2016 at 12:40 AM, Hannes Frederic Sowa
[off-list ref] wrote:
quoted
On 24.08.2016 16:24, Nikolay Borisov wrote:
[SNIP]
quoted
One commit which could have to do with that is
commit fc64869c48494a401b1fb627c9ecc4e6c1d74b0d
Author: Andrey Ryabinin [off-list ref]
Date: Wed May 18 19:19:27 2016 +0300
net: sock: move ->sk_shutdown out of bitfields.
but that is only a wild guess.
Which unix_sock did you extract specifically in the url you provided? In
unix_notinflight we are specifically checking an unix domain socket that
is itself being transferred over another af_unix domain socket and not
the unix domain socket being released at this point.
So this is the state of the socket that is being passed to
unix_notinflight. I have a complete crashdump so if you need more info
to diagnose it I'm happy to provide it. I'm not too familiar with the
code in question so I will need a bit of time to grasp what actually
is happening.
Would probably be helpful. I couldn't spot anything so far
unfortunately. Also moving sockets over sockets which get closed
inflight seemed to work fine.
On Wed, Aug 24, 2016 at 11:40 PM, Hannes Frederic Sowa
[off-list ref] wrote:
On 24.08.2016 16:24, Nikolay Borisov wrote:
quoted
Hello,
I hit the following BUG:
[1851513.239831] ------------[ cut here ]------------
[1851513.240079] kernel BUG at net/unix/garbage.c:149!
[1851513.240313] invalid opcode: 0000 [#1] SMP
[1851513.248320] CPU: 37 PID: 11683 Comm: nginx Tainted: G O 4.4.14-clouder3 #26
[1851513.248719] Hardware name: Supermicro X10DRi/X10DRi, BIOS 1.1 04/14/2015
[1851513.248966] task: ffff883b0f6f0000 ti: ffff880189cf0000 task.ti: ffff880189cf0000
[1851513.249361] RIP: 0010:[<ffffffff815f895d>] [<ffffffff815f895d>] unix_notinflight+0x8d/0x90
[1851513.249846] RSP: 0018:ffff880189cf3cf8 EFLAGS: 00010246
[1851513.250082] RAX: ffff883b05491968 RBX: ffff883b05491680 RCX: ffff8807f9967330
[1851513.250476] RDX: 0000000000000001 RSI: ffff882e6d8bae00 RDI: ffffffff82073f10
[1851513.250886] RBP: ffff880189cf3d08 R08: ffff880cbc70e200 R09: 0000000180200001
[1851513.251280] R10: ffff883fff3b9dc0 R11: ffffea0032f1c380 R12: ffff883fbaf50000
[1851513.251674] R13: ffffffff815f6354 R14: ffff881a7c77b140 R15: ffff881a7c7792c0
[1851513.252083] FS: 00007f4f19573720(0000) GS:ffff883fff3a0000(0000) knlGS:0000000000000000
[1851513.252481] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[1851513.252717] CR2: 00000000013062d8 CR3: 0000001712f32000 CR4: 00000000001406e0
[1851513.253116] Stack:
[1851513.253345] 00000000ffffffff ffff880189cf3d40 ffff880189cf3d28 ffffffff815f4383
[1851513.254022] ffff8839ee11a800 ffff8839ee11a800 ffff880189cf3d60 ffffffff815f53b8
[1851513.254685] 0000000000000000 ffff883406788de0 0000000000000000 0000000000000000
[1851513.255360] Call Trace:
[1851513.255594] [<ffffffff815f4383>] unix_detach_fds.isra.19+0x43/0x50
[1851513.255851] [<ffffffff815f53b8>] unix_destruct_scm+0x48/0x80
[1851513.256090] [<ffffffff815384af>] skb_release_head_state+0x4f/0xb0
[1851513.256328] [<ffffffff81538522>] skb_release_all+0x12/0x30
[1851513.256564] [<ffffffff81538592>] kfree_skb+0x32/0xa0
[1851513.256810] [<ffffffff815f6354>] unix_release_sock+0x1e4/0x2c0
[1851513.257046] [<ffffffff815f6450>] unix_release+0x20/0x30
[1851513.257284] [<ffffffff8152fbcf>] sock_release+0x1f/0x80
[1851513.257521] [<ffffffff8152fc42>] sock_close+0x12/0x20
[1851513.257769] [<ffffffff8119a8aa>] __fput+0xea/0x1f0
[1851513.258005] [<ffffffff8119a9ee>] ____fput+0xe/0x10
[1851513.258244] [<ffffffff8106fccf>] task_work_run+0x7f/0xb0
[1851513.258488] [<ffffffff81002210>] exit_to_usermode_loop+0xc0/0xd0
[1851513.258728] [<ffffffff81002a90>] syscall_return_slowpath+0x80/0xf0
[1851513.258983] [<ffffffff816147b4>] int_ret_from_sys_call+0x25/0x9f
[1851513.259222] Code: 7e 5b 41 5c 5d c3 48 8b 8b e8 02 00 00 48 8b 93 f0 02 00 00 48 89 51 08 48 89 0a 48 89 83 e8 02 00 00 48 89 83 f0 02 00 00 eb b8 <0f> 0b 90 0f 1f 44 00 00 55 48 c7 c7 10 3f 07 82 48 89 e5 41 54
[1851513.268473] RIP [<ffffffff815f895d>] unix_notinflight+0x8d/0x90
[1851513.268793] RSP <ffff880189cf3cf8>
That's essentially BUG_ON(list_empty(&u->link));
I see that all the code involving the ->link member hasn't really been
touched since it was introduced in 2007. So this must be a latent bug.
This is the first time I've observed it. The state
of the struct unix_sock can be found here http://sprunge.us/WCMW . Evidently,
there are no inflight sockets.
Weird. If it was the BUG_ON(!list_empty(&u->link)) I'd understand,
because the code in scan children looks fishy: what prevents "embryos"
from fledging to full socket status and going in-flight?
But this one, I cannot imagine any scenario.
Can we have access to the crashdump?
Thanks,
Miklos
On Sat, Aug 27, 2016 at 11:55 AM, Miklos Szeredi [off-list ref] wrote:
On Wed, Aug 24, 2016 at 11:40 PM, Hannes Frederic Sowa
[off-list ref] wrote:
quoted
On 24.08.2016 16:24, Nikolay Borisov wrote:
quoted
Hello,
I hit the following BUG:
[1851513.239831] ------------[ cut here ]------------
[1851513.240079] kernel BUG at net/unix/garbage.c:149!
[1851513.240313] invalid opcode: 0000 [#1] SMP
[1851513.248320] CPU: 37 PID: 11683 Comm: nginx Tainted: G O 4.4.14-clouder3 #26
[1851513.248719] Hardware name: Supermicro X10DRi/X10DRi, BIOS 1.1 04/14/2015
[1851513.248966] task: ffff883b0f6f0000 ti: ffff880189cf0000 task.ti: ffff880189cf0000
[1851513.249361] RIP: 0010:[<ffffffff815f895d>] [<ffffffff815f895d>] unix_notinflight+0x8d/0x90
[1851513.249846] RSP: 0018:ffff880189cf3cf8 EFLAGS: 00010246
[1851513.250082] RAX: ffff883b05491968 RBX: ffff883b05491680 RCX: ffff8807f9967330
[1851513.250476] RDX: 0000000000000001 RSI: ffff882e6d8bae00 RDI: ffffffff82073f10
[1851513.250886] RBP: ffff880189cf3d08 R08: ffff880cbc70e200 R09: 0000000180200001
[1851513.251280] R10: ffff883fff3b9dc0 R11: ffffea0032f1c380 R12: ffff883fbaf50000
[1851513.251674] R13: ffffffff815f6354 R14: ffff881a7c77b140 R15: ffff881a7c7792c0
[1851513.252083] FS: 00007f4f19573720(0000) GS:ffff883fff3a0000(0000) knlGS:0000000000000000
[1851513.252481] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[1851513.252717] CR2: 00000000013062d8 CR3: 0000001712f32000 CR4: 00000000001406e0
[1851513.253116] Stack:
[1851513.253345] 00000000ffffffff ffff880189cf3d40 ffff880189cf3d28 ffffffff815f4383
[1851513.254022] ffff8839ee11a800 ffff8839ee11a800 ffff880189cf3d60 ffffffff815f53b8
[1851513.254685] 0000000000000000 ffff883406788de0 0000000000000000 0000000000000000
[1851513.255360] Call Trace:
[1851513.255594] [<ffffffff815f4383>] unix_detach_fds.isra.19+0x43/0x50
[1851513.255851] [<ffffffff815f53b8>] unix_destruct_scm+0x48/0x80
[1851513.256090] [<ffffffff815384af>] skb_release_head_state+0x4f/0xb0
[1851513.256328] [<ffffffff81538522>] skb_release_all+0x12/0x30
[1851513.256564] [<ffffffff81538592>] kfree_skb+0x32/0xa0
[1851513.256810] [<ffffffff815f6354>] unix_release_sock+0x1e4/0x2c0
[1851513.257046] [<ffffffff815f6450>] unix_release+0x20/0x30
[1851513.257284] [<ffffffff8152fbcf>] sock_release+0x1f/0x80
[1851513.257521] [<ffffffff8152fc42>] sock_close+0x12/0x20
[1851513.257769] [<ffffffff8119a8aa>] __fput+0xea/0x1f0
[1851513.258005] [<ffffffff8119a9ee>] ____fput+0xe/0x10
[1851513.258244] [<ffffffff8106fccf>] task_work_run+0x7f/0xb0
[1851513.258488] [<ffffffff81002210>] exit_to_usermode_loop+0xc0/0xd0
[1851513.258728] [<ffffffff81002a90>] syscall_return_slowpath+0x80/0xf0
[1851513.258983] [<ffffffff816147b4>] int_ret_from_sys_call+0x25/0x9f
[1851513.259222] Code: 7e 5b 41 5c 5d c3 48 8b 8b e8 02 00 00 48 8b 93 f0 02 00 00 48 89 51 08 48 89 0a 48 89 83 e8 02 00 00 48 89 83 f0 02 00 00 eb b8 <0f> 0b 90 0f 1f 44 00 00 55 48 c7 c7 10 3f 07 82 48 89 e5 41 54
[1851513.268473] RIP [<ffffffff815f895d>] unix_notinflight+0x8d/0x90
[1851513.268793] RSP <ffff880189cf3cf8>
That's essentially BUG_ON(list_empty(&u->link));
I see that all the code involving the ->link member hasn't really been
touched since it was introduced in 2007. So this must be a latent bug.
This is the first time I've observed it. The state
of the struct unix_sock can be found here http://sprunge.us/WCMW . Evidently,
there are no inflight sockets.
Weird. If it was the BUG_ON(!list_empty(&u->link)) I'd understand,
because the code in scan children looks fishy: what prevents "embryos"
from fledging to full socket status and going in-flight?
But this one, I cannot imagine any scenario.
Can we have access to the crashdump?
crash> list -H gc_inflight_list unix_sock.link -s unix_sock.inflight |
grep counter | cut -d= -f2 | awk '{s+=$1} END {print s}'
130
crash> p unix_tot_inflight
unix_tot_inflight = $2 = 135
We've lost track of a total of five inflight sockets, so it's not a
one-off thing. Really weird... Now off to sleep, maybe I'll dream of
the solution.
Btw. I notice that this is a patched kernel. Nothing in there that
could be relevant to this bug?
Thanks,
Miklos
On Tue, Aug 30, 2016 at 12:37 AM, Miklos Szeredi [off-list ref] wrote:
On Sat, Aug 27, 2016 at 11:55 AM, Miklos Szeredi [off-list ref] wrote:
crash> list -H gc_inflight_list unix_sock.link -s unix_sock.inflight |
grep counter | cut -d= -f2 | awk '{s+=$1} END {print s}'
130
crash> p unix_tot_inflight
unix_tot_inflight = $2 = 135
We've lost track of a total of five inflight sockets, so it's not a
one-off thing. Really weird... Now off to sleep, maybe I'll dream of
the solution.
Okay, found one bug: gc assumes that in-flight sockets that don't have
an external ref can't gain one while unix_gc_lock is held. That is
true because unix_notinflight() will be called before detaching fds,
which takes unix_gc_lock. Only MSG_PEEK was somehow overlooked. That
one also clones the fds, also keeping them in the skb. But through
MSG_PEEK an external reference can definitely be gained without ever
touching unix_gc_lock.
Not sure whether the reported bug can be explained by this. Can you
confirm the MSG_PEEK was used in the setup?
Does someone want to write a stress test for SCM_RIGHTS + MSG_PEEK?
Anyway, attaching a fix that works by acquiring unix_gc_lock in case
of MSG_PEEK also. It is trivially correct, but I haven't tested it.
Thanks,
Miklos
From: Nikolay Borisov <hidden> Date: 2016-08-30 09:31:12
On 08/30/2016 12:18 PM, Miklos Szeredi wrote:
On Tue, Aug 30, 2016 at 12:37 AM, Miklos Szeredi [off-list ref] wrote:
quoted
On Sat, Aug 27, 2016 at 11:55 AM, Miklos Szeredi [off-list ref] wrote:
quoted
crash> list -H gc_inflight_list unix_sock.link -s unix_sock.inflight |
grep counter | cut -d= -f2 | awk '{s+=$1} END {print s}'
130
crash> p unix_tot_inflight
unix_tot_inflight = $2 = 135
We've lost track of a total of five inflight sockets, so it's not a
one-off thing. Really weird... Now off to sleep, maybe I'll dream of
the solution.
Okay, found one bug: gc assumes that in-flight sockets that don't have
an external ref can't gain one while unix_gc_lock is held. That is
true because unix_notinflight() will be called before detaching fds,
which takes unix_gc_lock. Only MSG_PEEK was somehow overlooked. That
one also clones the fds, also keeping them in the skb. But through
MSG_PEEK an external reference can definitely be gained without ever
touching unix_gc_lock.
Not sure whether the reported bug can be explained by this. Can you
confirm the MSG_PEEK was used in the setup?
Does someone want to write a stress test for SCM_RIGHTS + MSG_PEEK?
Anyway, attaching a fix that works by acquiring unix_gc_lock in case
of MSG_PEEK also. It is trivially correct, but I haven't tested it.
I have no way of being 100% sure but looking through nginx's source code
it seems they do utilize MSG_PEEK on several occasions. This issue has
been apparently very hard to reproduce since I have 100s of servers
running a lot of NGINX processes and this has been triggered only once.
On a different note - if I inspect a live node without this patch should
the discrepancy between the gc_inflight_list and the unix_tot_inflight
be present VS with this patch applied?
On Tue, Aug 30, 2016 at 11:31 AM, Nikolay Borisov [off-list ref] wrote:
On 08/30/2016 12:18 PM, Miklos Szeredi wrote:
quoted
On Tue, Aug 30, 2016 at 12:37 AM, Miklos Szeredi [off-list ref] wrote:
quoted
On Sat, Aug 27, 2016 at 11:55 AM, Miklos Szeredi [off-list ref] wrote:
quoted
crash> list -H gc_inflight_list unix_sock.link -s unix_sock.inflight |
grep counter | cut -d= -f2 | awk '{s+=$1} END {print s}'
130
crash> p unix_tot_inflight
unix_tot_inflight = $2 = 135
We've lost track of a total of five inflight sockets, so it's not a
one-off thing. Really weird... Now off to sleep, maybe I'll dream of
the solution.
Okay, found one bug: gc assumes that in-flight sockets that don't have
an external ref can't gain one while unix_gc_lock is held. That is
true because unix_notinflight() will be called before detaching fds,
which takes unix_gc_lock. Only MSG_PEEK was somehow overlooked. That
one also clones the fds, also keeping them in the skb. But through
MSG_PEEK an external reference can definitely be gained without ever
touching unix_gc_lock.
Not sure whether the reported bug can be explained by this. Can you
confirm the MSG_PEEK was used in the setup?
Does someone want to write a stress test for SCM_RIGHTS + MSG_PEEK?
Anyway, attaching a fix that works by acquiring unix_gc_lock in case
of MSG_PEEK also. It is trivially correct, but I haven't tested it.
I have no way of being 100% sure but looking through nginx's source code
it seems they do utilize MSG_PEEK on several occasions. This issue has
been apparently very hard to reproduce since I have 100s of servers
running a lot of NGINX processes and this has been triggered only once.
On a different note - if I inspect a live node without this patch should
the discrepancy between the gc_inflight_list and the unix_tot_inflight
be present VS with this patch applied?
May well be, since in the vmcore 4 in-flight sockets were "lost"
before triggering the bug. I guess the best way to check is with a
systemtap script that walks the list with the gc lock.
Thanks,
Miklos
From: Hannes Frederic Sowa <hidden> Date: 2016-09-01 09:13:06
On 30.08.2016 11:18, Miklos Szeredi wrote:
On Tue, Aug 30, 2016 at 12:37 AM, Miklos Szeredi [off-list ref] wrote:
quoted
On Sat, Aug 27, 2016 at 11:55 AM, Miklos Szeredi [off-list ref] wrote:
quoted
crash> list -H gc_inflight_list unix_sock.link -s unix_sock.inflight |
grep counter | cut -d= -f2 | awk '{s+=$1} END {print s}'
130
crash> p unix_tot_inflight
unix_tot_inflight = $2 = 135
We've lost track of a total of five inflight sockets, so it's not a
one-off thing. Really weird... Now off to sleep, maybe I'll dream of
the solution.
Okay, found one bug: gc assumes that in-flight sockets that don't have
an external ref can't gain one while unix_gc_lock is held. That is
true because unix_notinflight() will be called before detaching fds,
which takes unix_gc_lock. Only MSG_PEEK was somehow overlooked. That
one also clones the fds, also keeping them in the skb. But through
MSG_PEEK an external reference can definitely be gained without ever
touching unix_gc_lock.
Not sure whether the reported bug can be explained by this. Can you
confirm the MSG_PEEK was used in the setup?
Does someone want to write a stress test for SCM_RIGHTS + MSG_PEEK?
Anyway, attaching a fix that works by acquiring unix_gc_lock in case
of MSG_PEEK also. It is trivially correct, but I haven't tested it.
You can use spin_unlock_wait in unix_gc_barrier to make it a bit more
lightweight.
Anyway, all of the scans on the socket receive queues are actually
protected by the appropriate locks again, I didn't see a way were we
could result in such a crash because of concurrent modification of the
receive queue. Do you have any hints or looked into this more closely?
Thanks,
Hannes
From: Nikolay Borisov <hidden> Date: 2016-09-27 14:16:41
[Added Dave Miller to see what's the status of this patch]
On 08/30/2016 12:18 PM, Miklos Szeredi wrote:
On Tue, Aug 30, 2016 at 12:37 AM, Miklos Szeredi [off-list ref] wrote:
quoted
On Sat, Aug 27, 2016 at 11:55 AM, Miklos Szeredi [off-list ref] wrote:
quoted
crash> list -H gc_inflight_list unix_sock.link -s unix_sock.inflight |
grep counter | cut -d= -f2 | awk '{s+=$1} END {print s}'
130
crash> p unix_tot_inflight
unix_tot_inflight = $2 = 135
We've lost track of a total of five inflight sockets, so it's not a
one-off thing. Really weird... Now off to sleep, maybe I'll dream of
the solution.
Okay, found one bug: gc assumes that in-flight sockets that don't have
an external ref can't gain one while unix_gc_lock is held. That is
true because unix_notinflight() will be called before detaching fds,
which takes unix_gc_lock. Only MSG_PEEK was somehow overlooked. That
one also clones the fds, also keeping them in the skb. But through
MSG_PEEK an external reference can definitely be gained without ever
touching unix_gc_lock.
Not sure whether the reported bug can be explained by this. Can you
confirm the MSG_PEEK was used in the setup?
Does someone want to write a stress test for SCM_RIGHTS + MSG_PEEK?
Anyway, attaching a fix that works by acquiring unix_gc_lock in case
of MSG_PEEK also. It is trivially correct, but I haven't tested it.
Thanks,
Miklos
Why would I apply a patch that's an RFC, doesn't have a proper commit
message, lacks a proper signoff, and also lacks ACK's and feedback
from other knowledgable developers?