Also, another major benefit of not using flock() comes when using NFS (probably a very rare circumstance, but not entirely impossibile).
It is possible to use the presence of a file (with the same name) to indicate an "active" lock: such file should store the PID of the process that is requiring the lock. If a lock is found with a PID that does not exist, then such lock is considered invalid and it is removed. That is it really... Regards, Guido On the 24th of April 2017 19:51:27 CEST, Guido Trentalancia <[email protected]> wrote: >Yes, we already discussed this possibile race condition. > >Usually there is only one system administrator operating on the >semanage store, nevertheless it's worth having a robust locking >mechanism... > >This patch either needs further work to avoid using flock() and instead >using a simpler file lock mechanism with the added benefit of having a >cleaner filesystem without confusing stale files around or we just drop >the patch given it is not essential to keep things working. > >Regards, > >Guido > >On the 24th of April 2017 14:08:22 CEST, Alan Jenkins ><[email protected]> wrote: >>*expands thread >> >>Sorry, I see this has already been addressed. >> >> >>On 24/04/17 13:06, Alan Jenkins wrote: >>> On 20/04/17 15:38, Guido Trentalancia wrote: >>>> Remove semanage read and transaction lock files upon releasing >>>> them. >>> >>> What prevents this sequence? >>> >>> A release lock >>> B acquire lock >>> A unlink lock file >>> C create lock file >>> C acquire lock >>> >>>> Signed-off-by: Guido Trentalancia >>>> <[email protected]> >>>> --- >>>> src/semanage_store.c | 2 ++ >>>> 1 file changed, 2 insertions(+) >>>> >>>> diff -pruN a/src/semanage_store.c b/src/semanage_store.c >>>> --- a/src/semanage_store.c 2016-10-14 17:31:26.000000000 +0200 >>>> +++ b/src/semanage_store.c 2017-04-03 09:32:24.093627962 +0200 >>>> @@ -1904,6 +1904,7 @@ void semanage_release_trans_lock(semanag >>>> close(sh->u.direct.translock_file_fd); >>>> sh->u.direct.translock_file_fd = -1; >>>> } >>>> + unlink(semanage_files[SEMANAGE_TRANS_LOCK]); >>>> errno = errsv; >>>> } >>>> @@ -1917,6 +1918,7 @@ void semanage_release_active_lock(semana >>>> close(sh->u.direct.activelock_file_fd); >>>> sh->u.direct.activelock_file_fd = -1; >>>> } >>>> + unlink(semanage_files[SEMANAGE_READ_LOCK]); >>>> errno = errsv; >>>> } >>> >>> >>>
