linux-kernel - Re: [ipc,shm] BUG: lock held when returning to user space!

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Date:	Sun, 21 Jul 2013 00:02:35 +0800
From:	Xiaotian Feng <xtfeng@...il.com>
To:	Fengguang Wu <fengguang.wu@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Davidlohr Bueso <davidlohr.bueso@...com>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [ipc,shm] BUG: lock held when returning to user space!

On Sat, Jul 20, 2013 at 9:13 PM, Fengguang Wu <fengguang.wu@...el.com> wrote:
> Greetings,
>
> I got the below dmesg and the first bad commit is
>
> commit c5d0282a0405b0a81fa3390e4230e4cbb3ced7a2
> Author: Davidlohr Bueso <davidlohr.bueso@...com>
> Date:   Fri Jul 19 09:56:58 2013 +1000
>
>     ipc,shm: shorten critical region for shmat
>
>     Similar to other system calls, acquire the kern_ipc_perm lock after doing
>     the initial permission and security checks.
>
>     Signed-off-by: Davidlohr Bueso <davidlohr.bueso@...com>
>     Tested-by: Sedat Dilek <sedat.dilek@...il.com>
>     Cc: Rik van Riel <riel@...hat.com>
>     Cc: Manfred Spraul <manfred@...orfullife.com>
>     Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
>
> [   20.702156]
> [   20.702493] ================================================
> [   20.703511] [ BUG: lock held when returning to user space! ]
> [   20.704532] 3.11.0-rc1-next-20130719 #50 Not tainted
> [   20.705416] ------------------------------------------------
> [   20.706425] trinity-child0/174 is leaving the kernel with locks still held!
> [   20.707638] 1 lock held by trinity-child0/174:
> [   20.708475]  #0:  (rcu_read_lock){.+.+..}, at: [<ffffffff814a8491>] do_shmat+0xe1/0x500
>

----
ns = current->nsproxy->ipc_ns;
- shp = shm_lock_check(ns, shmid);
+ rcu_read_lock();
+ shp = shm_obtain_object_check(ns, shmid);
if (IS_ERR(shp)) {
err = PTR_ERR(shp);
goto out;
----

If shm_obtain_object_check() failed, goto out will return with
rcu_read_lock() held.  I think following patch should cure this.

diff --git a/ipc/shm.c b/ipc/shm.c
index 59f2194..cb2ceda 100644
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -1093,7 +1093,7 @@ long do_shmat(int shmid, char __user *shmaddr,
int shmflg, ulong *raddr,
  shp = shm_obtain_object_check(ns, shmid);
  if (IS_ERR(shp)) {
  err = PTR_ERR(shp);
- goto out;
+ goto out_unlock;
  }

  err = -EACCES;




> git bisect start c1f631b9a68251007a6353041ae90f9f7dca771c d03792f9db9b892f494d3aa19d767ddf0365d1ff --
> git bisect good 10a3f1f902465ae1320cc95a3284fd3697e05dd8  # 11:14     65+  binfmt_elf.c: use get_random_int() to fix entropy depleting
> git bisect  bad dac28788378838efb63e37a7eabd7729d97aba6b  # 11:32      0-  dcache: remove dentries from LRU before putting on dispose list
> git bisect good 3140b2ed6dfe5c9e5eca371c77ca85dca05321d4  # 11:50     65+  ipc,shm: introduce shmctl_nolock
> git bisect  bad 48a91248649fa3327bd8a31c114ee9149a07f3a7  # 12:04      0-  staging/lustre/ldlm: convert to shrinkers to count/scan API
> git bisect good 98b78126a51aa5d3ee6d5dae5768e0d16deeeaa3  # 12:14     65+  ipc,shm: cleanup do_shmat pasta
> git bisect  bad 36ccfd799cad33e2edd5c14ac8776b33e63d195b  # 12:14      0-  ipc: rename ids->rw_mutex
> git bisect  bad c5d0282a0405b0a81fa3390e4230e4cbb3ced7a2  # 12:14      0-  ipc,shm: shorten critical region for shmat
> git bisect good 98b78126a51aa5d3ee6d5dae5768e0d16deeeaa3  # 15:34    195+  ipc,shm: cleanup do_shmat pasta
> git bisect  bad c1f631b9a68251007a6353041ae90f9f7dca771c  # 15:34      0-  Add linux-next specific files for 20130719
> git bisect good 709b465ee655387c4ec056383fa27f16c64f48db  # 18:21    195+  Revert "ipc,shm: shorten critical region for shmat"
> git bisect good d471ce53b1fab60110e4e9f647a345cea31752de  # 18:44    195+  Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/rw/uml
> git bisect  bad c1f631b9a68251007a6353041ae90f9f7dca771c  # 18:44      0-  Add linux-next specific files for 20130719
>
> Thanks,
> Fengguang
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