Date: Thu, 9 May 2013 11:25:38 +0300 From: Konstantin Belousov <kostikbel@gmail.com> To: John Baldwin <jhb@freebsd.org> Cc: arch@freebsd.org Subject: Re: Extending MADV_PROTECT Message-ID: <20130509082538.GQ3047@kib.kiev.ua> In-Reply-To: <201305081209.49429.jhb@freebsd.org> References: <201305071433.27993.jhb@freebsd.org> <20130508095827.GK3047@kib.kiev.ua> <201305081209.49429.jhb@freebsd.org>
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--cw81t83UHTonwpSu Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Wed, May 08, 2013 at 12:09:49PM -0400, John Baldwin wrote: > On Wednesday, May 08, 2013 5:58:27 am Konstantin Belousov wrote: > > On Tue, May 07, 2013 at 02:33:27PM -0400, John Baldwin wrote: > > > One of the issues I have with our current MADV_PROTECT is that it > > > isn't very administrative-friendly. That is, as a sysadmin I can't > > > easily protect arbitrary processes from the OOM killer. Instead, the > > > binary has to be changed to invoke madvise(). Furthermore, once the > > > protection is granted it can't be revoked. Also, any binaries that > > > want this have to be run as root. Instead, I would like to be able > > > to both set and revoke this for existing processes and possibly even > > > allow it to be inherited (so I can tag a top-level daemon that forks > > > and have all its future children be protected for example). To that > > > end I've whipped up a simple patch (against 8, but should port to > > > HEAD easily if folks think it is a good idea) to add a new pprotect() > > > system call and userland program (protect) that can be used similar to > > > ktrace(1) either as a modifier when running a new program or as a tool > > > for setting or clearing protection for existing processes. > > > > > > The inherit feature isn't implemented yet, but it should be simple > > > to do. One would simply need a new flag that PPROT_INHERIT sets that > > > is checked on fork and propagates P_PROTECTED if it is set. Also, > > > one other thought I had is that at some point we might want to make > > > P_PROTECTED more fine-grained, e.g. by allowing for OOM "priorities". > > > To that end, it may make sense to add a new argument to protect, > > > though you could also reserve part of the 'op' parameter to encode a > > > priority. > >=20 > > Wouldn't the pprot_setchildren() miss a child for which the new pid and > > struct proc are already allocated in the do_fork(), but which is not yet > > linked into the process tree ? If true, I think this does not > > fulfill the promise of the PPROT_DESCEND. >=20 > ktrace has the same issue, and really, this is just a race. If the user > had run the command a few nanoseconds earlier the proc wouldn't be alloca= ted > at all, and I doubt a user would notice the difference in those two cases. > If you are doing this programmatically then that is a race that the progr= am > can handle. It isn't any different from having a new process begin its > fork() a few nanoseconds after this returns either. This is why if you > want that behavior you would use -di (and applies equally to ktrace). So to get this correct, a person first should enable inheritance, and only then turn on the protection on the subtree ? This sounds somewhat sloppy, but fine. >=20 > > It seems that the patch posted missed the chunk for sys/proc.h. > > For HEAD, you probably need e.g. p_flag2 and P2_PROTECTED instead. >=20 > P_PROTECTED already exists on both HEAD and 8.x (the MADV_PROTECT it is > extending is quite old). What we would need a p_flag2 for would be to > add a new P_PROTECTED_INHERIT if we decided we wanted to support that. >=20 > > Since the syscall is mean to be extended in the future, would it make > > more sense to add a multiplexer, e.g. procctl(2), one operation of which > > would be PROCCTL_PROTECT ? >=20 > Do we expect it to do more than adjust protection? We already have a few > other process-control system calls (e.g. ptrace()). It's hard to ensure > it is sufficiently generic when only abstracting from one use case. You mentioned a priority, and I think ability to pass a structure to the sub-function of the syscall is better then carving bits in the int argument, or introducing a new syscall. --cw81t83UHTonwpSu Content-Type: application/pgp-signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.19 (FreeBSD) iQIcBAEBAgAGBQJRi12BAAoJEJDCuSvBvK1B2tsQAKgeRYX3QS2qPKjCNSmXpHJS ZueorZhQus7sbHU5gj4ur3Q0dC2KxH6/Zg7HeVBYnIZ7Re02RNifTENoUOfY3h6D WGrdCubKBh0ME/QlLfdQ4GGX86JmzG7UOAvgAAH267h9T8Ly7tQexEPTIZwxRwcj MYJdSPWS6D4EIfHxdT/Ao8ZMZ5eF3MLYwpTPBiALEj/Dm8xA7xLEGshJdKCVhDtY jbTh61LeGuNKyZXoVuR2S25vwxac5RSLrZhlxiKNRsy6XuAJLzM7EIDZHfQ50n+K xPSTIXZ9bMVMn8CYuGv11Xi6lLX2ipb5cGh7aGXtvRjF7ii3x0CrwuWL2FPKmJof W7Hro4U2hJaOFtks566RPzcfNPfEfjonuhJGwJSCXV1zSESHCYulVAKGJb8KJ7wj K5kj2DeBfm+bp23iCEFUEnabfXCJibYrbFh9mRuMYbQTJIK4XM7k4Rmkh7Iu2QqM XhPvFFSU0wBWoBbzc26Ngkr/OLjQgTktj6oS/nqKN47fc9RLOORCszefJwGJ2JXd VczjAQSP7jJB4qkeHrgNK0ZVUzt6HDArRnNK8DIltZDLZFiVwoxLkg9UvRpHsJma Gp0OkqpIj8sOquSoIdZ6GA4tsQzE4d4//A3444JtX6hpKdkjBRedGO2ai+Gk1MR5 wXJgyd5AwstbbgGNJ2X5 =pKFU -----END PGP SIGNATURE----- --cw81t83UHTonwpSu--
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