Re: [PATCH v2 9/8] don't fool lockdep in freeze_super() and thaw_super() paths
From: Oleg Nesterov
Date: Thu Aug 13 2015 - 10:00:58 EST
On 08/13, Jan Kara wrote:
> On Wed 12-08-15 15:11:38, Oleg Nesterov wrote:
> > On 08/11, Oleg Nesterov wrote:
> > >
> > > The only essential change is that I dropped the lockdep improvements
> > > as we discussed. This means that 8/8 was changed a bit, and I decided
> > > to add the new documentation patch, see 3/8.
> > Update: The recent
> > [PATCH 0/2] xfs: kill lockdep false positives from readdir
> > changes from Dave fixed the problems ILOCK false-positives. So we can
> > add the additional patch which (modulo comments) just turns v2 back into
> > v1.
> > Dave, Jan, you seem to agree with these patches. How should we route
> > this all?
> Regarding the routing, ideally Al Viro should take these as a VFS
OK. I'll send v3.
But to remind, this particular patch depends on Dave's fixes, so I will
send it later.
And I forgot to mention that I have another patch which removes the
trylock hack from __sb_start_write() as Dave suggested, it passed the
tests. But again, I'd really like to send it separately so that it can
be reverted in (unlikely) case something else does recursive read_lock().
> > Subject: [PATCH v2 9/8] don't fool lockdep in freeze_super() and thaw_super() paths
> > sb_wait_write()->percpu_rwsem_release() fools lockdep to avoid the
> > false-positives. Now that xfs was fixed by Dave we can remove it and
> > change freeze_super() and thaw_super() to run with s_writers.rw_sem
> > locks held; we add two trivial helpers for that, sb_freeze_release()
> > and sb_freeze_acquire().
> > While at it, kill the outdated part of the comment above sb_wait_write.
> > Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
> The patch looks good. Just one nit:
> > + for (level = SB_FREEZE_LEVELS; --level >= 0; )
> > + percpu_rwsem_release(sb->s_writers.rw_sem + level, 0, _THIS_IP_);
> It is more common (and to me more readable) to have the loop written as:
> for (level = SB_FREEZE_LEVELS - 1; level >= 0; level--)
> I agree what you do is shorter but IMHO it's just an unnecessary
> obfuscation :)
Agreed, will fix.
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