Re: CVS commit: src/sys/fs/tmpfs

["J. Hannken-Illjes" <hannken%eis.cs.tu-bs.de@localhost>]

On Jan 3, 2014, at 10:13 PM, Mindaugas Rasiukevicius 
<rmind%netbsd.org@localhost> wrote:

> "Juergen Hannken-Illjes" <hannken%netbsd.org@localhost> wrote:
>> Module Name: src
>> Committed By:        hannken
>> Date:                Fri Jan  3 09:53:12 UTC 2014
>> 
>> Modified Files:
>>      src/sys/fs/tmpfs: tmpfs_subr.c tmpfs_vnops.c
>> 
>> Log Message:
>> Fix a race where thread1 runs VOP_REMOVE() and gets preempted in
>> tmpfs_reclaim() before the call to tmpfs_free_node().  Thread2
>> runs VFS_FHTOVP() and gets a new vnode attached to the node thread1
>> is about to destroy.
>> 
>> Change tmpfs_alloc_node() to always assign non-zero generation number
>> and tmpfs_inactive() to set the generation number of unlinked nodes
>> to zero.
> 
> Can you explain how does this help?  It still seems racy to me.

Please describe the race in more detail.  Tmpfs_fhtovp() will fail
as soon as an unlinked tmpfs node drops its last vnode reference.

> Why not just check for tn_links == 0 in tmpfs_fhtovp()?

Because it is ok as long as the corresponding vnode is open/referenced.

--
J. Hannken-Illjes - hannken%eis.cs.tu-bs.de@localhost - TU Braunschweig 
(Germany)