On Mon, Oct 21, 2019 at 04:41:37PM -0500, Mike Christie wrote: > There are several storage drivers like dm-multipath, iscsi, tcmu-runner, > amd nbd that have userspace components that can run in the IO path. For > example, iscsi and nbd's userspace deamons may need to recreate a socket > and/or send IO on it, and dm-multipath's daemon multipathd may need to > send IO to figure out the state of paths and re-set them up. > > In the kernel these drivers have access to GFP_NOIO/GFP_NOFS and the > memalloc_*_save/restore functions to control the allocation behavior, > but for userspace we would end up hitting a allocation that ended up > writing data back to the same device we are trying to allocate for. I think this needs to describe the symptoms this results in. i.e. that this can result in deadlocking the IO path. > This patch allows the userspace deamon to set the PF_MEMALLOC* flags > with prctl during their initialization so later allocations cannot > calling back into them. > > Signed-off-by: Mike Christie <mchristi@xxxxxxxxxx> > --- .... > + case PR_SET_MEMALLOC: > + if (!capable(CAP_SYS_ADMIN)) > + return -EPERM; Wouldn't CAP_SYS_RAWIO (because it's required by kernel IO path drivers) or CAP_SYS_RESOURCE (controlling memory allocation behaviour) be more appropriate here? Which-ever is selected, the use should be added to the list above the definition of the capability in include/linux/capability.h... Otherwise looks fine to me. Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx
