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Subject[PATCH review 3/3] proc: Allow proc_free_inum to be called from any context

While testing the pid namespace code I hit this nasty warning.

[ 176.262617] ------------[ cut here ]------------
[ 176.263388] WARNING: at /home/eric/projects/linux/linux-userns-devel/kernel/softirq.c:160 local_bh_enable_ip+0x7a/0xa0()
[ 176.265145] Hardware name: Bochs
[ 176.265677] Modules linked in:
[ 176.266341] Pid: 742, comm: bash Not tainted 3.7.0userns+ #18
[ 176.266564] Call Trace:
[ 176.266564] [<ffffffff810a539f>] warn_slowpath_common+0x7f/0xc0
[ 176.266564] [<ffffffff810a53fa>] warn_slowpath_null+0x1a/0x20
[ 176.266564] [<ffffffff810ad9ea>] local_bh_enable_ip+0x7a/0xa0
[ 176.266564] [<ffffffff819308c9>] _raw_spin_unlock_bh+0x19/0x20
[ 176.266564] [<ffffffff8123dbda>] proc_free_inum+0x3a/0x50
[ 176.266564] [<ffffffff8111d0dc>] free_pid_ns+0x1c/0x80
[ 176.266564] [<ffffffff8111d195>] put_pid_ns+0x35/0x50
[ 176.266564] [<ffffffff810c608a>] put_pid+0x4a/0x60
[ 176.266564] [<ffffffff8146b177>] tty_ioctl+0x717/0xc10
[ 176.266564] [<ffffffff810aa4d5>] ? wait_consider_task+0x855/0xb90
[ 176.266564] [<ffffffff81086bf9>] ? default_spin_lock_flags+0x9/0x10
[ 176.266564] [<ffffffff810cab0a>] ? remove_wait_queue+0x5a/0x70
[ 176.266564] [<ffffffff811e37e8>] do_vfs_ioctl+0x98/0x550
[ 176.266564] [<ffffffff810b8a0f>] ? recalc_sigpending+0x1f/0x60
[ 176.266564] [<ffffffff810b9127>] ? __set_task_blocked+0x37/0x80
[ 176.266564] [<ffffffff810ab95b>] ? sys_wait4+0xab/0xf0
[ 176.266564] [<ffffffff811e3d31>] sys_ioctl+0x91/0xb0
[ 176.266564] [<ffffffff810a95f0>] ? task_stopped_code+0x50/0x50
[ 176.266564] [<ffffffff81939199>] system_call_fastpath+0x16/0x1b
[ 176.266564] ---[ end trace 387af88219ad6143 ]---

It turns out that spin_unlock_bh(proc_inum_lock) is not safe when
put_pid is called with another spinlock held and irqs disabled.

For now take the easy path and use spin_lock_irqsave(proc_inum_lock)
in proc_free_inum and spin_loc_irq in proc_alloc_inum(proc_inum_lock).

Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
---
fs/proc/generic.c | 13 +++++++------
1 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/fs/proc/generic.c b/fs/proc/generic.c
index e064f56..76ddae8 100644
--- a/fs/proc/generic.c
+++ b/fs/proc/generic.c
@@ -352,18 +352,18 @@ retry:
if (!ida_pre_get(&proc_inum_ida, GFP_KERNEL))
return -ENOMEM;

- spin_lock_bh(&proc_inum_lock);
+ spin_lock_irq(&proc_inum_lock);
error = ida_get_new(&proc_inum_ida, &i);
- spin_unlock_bh(&proc_inum_lock);
+ spin_unlock_irq(&proc_inum_lock);
if (error == -EAGAIN)
goto retry;
else if (error)
return error;

if (i > UINT_MAX - PROC_DYNAMIC_FIRST) {
- spin_lock_bh(&proc_inum_lock);
+ spin_lock_irq(&proc_inum_lock);
ida_remove(&proc_inum_ida, i);
- spin_unlock_bh(&proc_inum_lock);
+ spin_unlock_irq(&proc_inum_lock);
return -ENOSPC;
}
*inum = PROC_DYNAMIC_FIRST + i;
@@ -372,9 +372,10 @@ retry:

void proc_free_inum(unsigned int inum)
{
- spin_lock_bh(&proc_inum_lock);
+ unsigned long flags;
+ spin_lock_irqsave(&proc_inum_lock, flags);
ida_remove(&proc_inum_ida, inum - PROC_DYNAMIC_FIRST);
- spin_unlock_bh(&proc_inum_lock);
+ spin_unlock_irqrestore(&proc_inum_lock, flags);
}

static void *proc_follow_link(struct dentry *dentry, struct nameidata *nd)
--
1.7.5.4


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