From dfb2ea45becb198beeb75350d0b7b7ad9076a38f Mon Sep 17 00:00:00 2001 From: "Eric W. Biederman" Date: Fri, 21 Dec 2012 20:38:00 -0800 Subject: [PATCH] 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] [] warn_slowpath_common+0x7f/0xc0 [ 176.266564] [] warn_slowpath_null+0x1a/0x20 [ 176.266564] [] local_bh_enable_ip+0x7a/0xa0 [ 176.266564] [] _raw_spin_unlock_bh+0x19/0x20 [ 176.266564] [] proc_free_inum+0x3a/0x50 [ 176.266564] [] free_pid_ns+0x1c/0x80 [ 176.266564] [] put_pid_ns+0x35/0x50 [ 176.266564] [] put_pid+0x4a/0x60 [ 176.266564] [] tty_ioctl+0x717/0xc10 [ 176.266564] [] ? wait_consider_task+0x855/0xb90 [ 176.266564] [] ? default_spin_lock_flags+0x9/0x10 [ 176.266564] [] ? remove_wait_queue+0x5a/0x70 [ 176.266564] [] do_vfs_ioctl+0x98/0x550 [ 176.266564] [] ? recalc_sigpending+0x1f/0x60 [ 176.266564] [] ? __set_task_blocked+0x37/0x80 [ 176.266564] [] ? sys_wait4+0xab/0xf0 [ 176.266564] [] sys_ioctl+0x91/0xb0 [ 176.266564] [] ? task_stopped_code+0x50/0x50 [ 176.266564] [] 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" --- fs/proc/generic.c | 13 +++++++------ 1 file changed, 7 insertions(+), 6 deletions(-) diff --git a/fs/proc/generic.c b/fs/proc/generic.c index e064f562b1f7..76ddae83daa5 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) -- 2.20.1