On Wed, Oct 14, 2020 at 11:46:40AM +0200, Phil Sutter wrote: > On Tue, Oct 13, 2020 at 12:15:02PM +0200, Pablo Neira Ayuso wrote: > > On Tue, Oct 13, 2020 at 12:08:03PM +0200, Phil Sutter wrote: > > [...] > > > On Mon, Oct 12, 2020 at 02:54:50PM +0200, Pablo Neira Ayuso wrote: > > > [...] > > > > Patch LGTM, thanks Phil. > > > > > > > > What I don't clearly see yet is what scenario is triggering the bug in > > > > the existing code, if you don't mind to explain. > > > > > > See the test case attached to the patch: An other iptables-restore > > > process may add references (i.e., jumps) to a chain the own > > > iptables-restore process wants to delete. This should not be a problem > > > because these references are added to a chain that is being flushed by > > > the own process as well. But if that chain doesn't exist while the own > > > process fetches kernel's ruleset, this flush job is not created. > > > > Let me rephrase this: > > > > 1) process A fetches the ruleset, finds no chain C (no flush job then) > > 2) process B adds new chain C, flush job is present > > 3) process B adds the ruleset > > 4) process A appends rules to the existing chain C (because there is > > no flush job) > > > > Is this the scenario? If so, I wonder why the generation ID is not > > helping to refresh and retry. > > Not quite, let me try to put this more clearly: > > * Dump A: > | *filter > | :FOO - [0:0] # flush chain FOO > | -X BAR # remove chain BAR > | COMMIT > > * Dump B: > | *filter > | -A FOO -j BAR # reference BAR from a rule in FOO > | COMMIT > > * Kernel ruleset: > | *filter > | :BAR - [0:0] > | COMMIT > > * Process A: > * read dump A > * fetch cache > > * Process B: > * read dump B > * fetch ruleset > * commit to kernel > > * Process A: > * skip flush chain FOO job: not present > * add delete chain BAR job: chain exists > * commit fails (genid outdated) > * refresh transaction: > * delete chain BAR job remains active > * genid updated > * commit fails: can't remove chain BAR: EBUSY Makes sense. Thanks a lot for explaining. Probably you can include this in the commit description for the record. > I realize the test case is not quite effective, ruleset should be > emptied upon each iteration of concurrent restore job startup. Please, update the test and revamp.
