Re: [git pull] vfs fixes

[Al Viro <viro@ZenIV.linux.org.uk>]

On Fri, Sep 26, 2014 at 10:46:14PM +0200, Joachim Eastwood wrote:
> On 14 September 2014 21:47, Al Viro <viro@zeniv.linux.org.uk> wrote:
> > double iput() on failure exit in lustre, racy removal of spliced dentries
> > from ->s_anon in __d_materialise_dentry() plus a bunch of assorted RCU pathwalk
> > fixes.  Please, pull from the usual place -
> > git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs.git for-linus
> >
> > Shortlog:
> > Al Viro (5):
> >       [fix] lustre: d_make_root() does iput() on dentry allocation failure
> >       move the call of __d_drop(anon) into __d_materialise_unique(dentry, anon)
> >       fix bogus read_seqretry() checks introduced in b37199e
> >       don't bugger nd->seq on set_root_rcu() from follow_dotdot_rcu()
> >       be careful with nd->inode in path_init() and follow_dotdot_rcu()
> 
> Hi,
> 
> Commit 4023bfc9f351a7994 "be careful with nd->inode in path_init() and
> follow_dotdot_rcu(), seem to hang my ARM no-MMU platform when mounting
> the ramdisk.
> 
> 3.17-rc4 - works
> 3.17-rc5 - works with 4023bfc9f351a7994 reverted.
> 
> Boot log with from rc5:
> [ 5.810000] TCP: cubic registered
> [ 5.820000] NET: Registered protocol family 17
> [ 5.860000] lpc2k-rtc 40046000.rtc: hctosys: unable to read the hardware clock
> [ 5.910000] mmc_host mmc0: Bus speed (slot 0) = 12000000Hz (slot req
> 25000000Hz, actual 12000000HZ div = 0)
> [ 5.930000] mmc0: new SDHC card at address 0007
> [ 5.950000] mmcblk0: mmc0:0007 SD08G 7.42 GiB
> [ 6.150000] clk: Not disabling unused clocks
> [ 81.240000] random: nonblocking pool is initialized
> 
> And there it just hangs it seems.
> 
> 
> With patch reverted
> [ 5.810000] TCP: cubic registered
> [ 5.820000] NET: Registered protocol family 17
> [ 5.850000] lpc2k-rtc 40046000.rtc: hctosys: unable to read the hardware clock
> [ 6.100000] clk: Not disabling unused clocks
> [ 6.110000] RAMDISK: gzip image found at block 0
> [ 9.590000] VFS: Mounted root (ext2 filesystem) readonly on device 1:0.
> [ 9.600000] devtmpfs: mounted
> [ 9.610000] Freeing unused kernel memory: 68K (281e5000 - 281f6000)
> 
> And then user space starts.

*blink*  What happens to mmc-related messages on successful boot?  And what
in that commit could've possibly lead to those not being produced?

Another question: what happens if you revert a half of that commit?  There
are two separate parts, easy to isolate - one in follow_dotdot_rcu(), another
in path_init().  They deal with similar problems, but they are independent
from each other; which one is triggering that crap?

Al, really mystified...