On Thu, Apr 08, 2021 at 03:37:53AM +0200, Thomas Gleixner wrote: > Greg, > > On Fri, Apr 02 2021 at 09:54, Greg KH wrote: > > On Thu, Apr 01, 2021 at 11:59:25PM +0000, Luis Chamberlain wrote: > >> As for the syfs deadlock possible with drivers, this fixes it in a generic way: > >> > >> commit fac43d8025727a74f80a183cc5eb74ed902a5d14 > >> Author: Luis Chamberlain <mcgrof@xxxxxxxxxx> > >> Date: Sat Mar 27 14:58:15 2021 +0000 > >> > >> sysfs: add optional module_owner to attribute > >> > >> This is needed as otherwise the owner of the attribute > >> or group read/store might have a shared lock used on driver removal, > >> and deadlock if we race with driver removal. > >> > >> Signed-off-by: Luis Chamberlain <mcgrof@xxxxxxxxxx> > > > > No, please no. Module removal is a "best effort", if the system dies > > when it happens, that's on you. I am not willing to expend extra energy > > and maintance of core things like sysfs for stuff like this that does > > not matter in any system other than a developer's box. > > > > Lock data, not code please. Trying to tie data structure's lifespans > > to the lifespan of code is a tangled mess, and one that I do not want to > > add to in any form. > > > > sorry, > > Sorry, but you are fundamentaly off track here. This has absolutely > nothing to do with module removal. > > The point is that module removal is the reverse operation of module > insertion. So far so good. > > But module insertion can fail. So if you have nested functionalities > which hang off or are enabled by moduled insertion then any fail in that > sequence has to be able to roll back and clean up properly no matter > what. > > Which it turn makes modules removal a reverse operation of module > insertion. > > If you think otherwise, then please provide a proper plan how nested > operations like sysfs - not to talk about more complex things like multi > instance discovery which can happen inside a module insertion sequence > can be properly rolled back. > > Just declaring that rmmod is evil does not cut it. rmmod is the least of > the problems. If that fails, then a lot of rollback, failure handling > mechanisms are missing in the setup path already. > > Anything which cannot cleanly rollback no matter whether the fail or > rollback request happens at insertion time or later is broken by design. > > So either you declare module removal as disfunctional or you stop making > up semantically ill defined and therefore useless claims about it. > > Your argument in: > > https://lore.kernel.org/linux-block/YGbNpLKXfWpy0ZZa@xxxxxxxxx/ > > "Lock data, not code please. Trying to tie data structure's lifespans > to the lifespan of code is a tangled mess, and one that I do not want to > add to in any form" > > is just useless blurb because the fundamental purpose of discovery code > is to create the data structures which are tied to the code which is > associated to it. > > Please stop this 'module removal' is not supported nonsense unless you > can prove a complete indepenence of module init/discovery code to > subsequent discovered entities depending on it. Ok, but to be fair, trying to add the crazy hacks that were being proposed to sysfs for something that is obviously not a code path that can be taken by a normal user or operation is just not going to fly. Removing a module from a system has always been "let's try it and see!" type of operation for a very long time. While we try our best, doing horrible hacks for this rare type of thing are generally not considered a good idea which is why I said that. thanks, greg k-h
