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Date: Mon, 2 Jan 2012 20:49:45 +0100 From: Jan Kara <jack@...e.cz> To: Joel Becker <jlbec@...lplan.org> Cc: Jan Kara <jack@...e.cz>, linux-ext4@...r.kernel.org, akmp@...e.cz, rjw@...k.pl, Andrew Morton <akpm@...ux-foundation.org> Subject: Re: [PATCH] jbd: Remove j_barrier mutex On Tue 27-12-11 10:51:00, Joel Becker wrote: > On Thu, Dec 22, 2011 at 03:07:45PM +0100, Jan Kara wrote: > > j_barrier mutex is used for serializing different journal lock operations. The > > problem with it is that e.g. FIFREEZE ioctl results in process leaving kernel > > with j_barrier mutex held which makes lockdep freak out. Also hibernation code > > wants to freeze filesystem but it cannot do so because it then cannot hibernate > > the system because of mutex being locked. > > > > So we remove j_barrier mutex and use direct wait on j_barrier_count instead. > > Since locking journal is a rare operation we don't have to care about fairness > > or such things. > > > > CC: Andrew Morton <akpm@...ux-foundation.org> > > Signed-off-by: Jan Kara <jack@...e.cz> > > Strikes me as pretty reasonable. > > > void journal_lock_updates(journal_t *journal) > > { > > DEFINE_WAIT(wait); > > > > +wait: > > + /* Wait for previous locked operation to finish */ > > + wait_event(journal->j_wait_transaction_locked, > > + journal->j_barrier_count == 0); > > + > > spin_lock(&journal->j_state_lock); > > + /* > > + * Check reliably under the lock whether we are the ones winning the race > > + * and locking the journal > > + */ > > + if (journal->j_barrier_count > 0) { > > + spin_unlock(&journal->j_state_lock); > > + goto wait; > > + } > > I suppose I'd prefer: > > do { > wait_event(journal->j_wait_transaction_locked, > journal->j_barrier_count == 0); > > spin_lock(&journal->j_state_lock); > if (journal->j_barrier_count == 0) > break; > spin_unlock(&journal->j_state_lock); > } while (1); > ++journal->j_barrier_count; > > because I hate using goto for trivial loops, but that's a nitpick. Frankly, I'm more used to parsing simple goto loops like mine than infinite-loop + break statements in cases like this. So I'll take the liberty of being a maintainer and keep the goto. But thanks for the suggestion anyway. > ACK. Thanks for review! Honza -- Jan Kara <jack@...e.cz> SUSE Labs, CR -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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