On 10/21/2019 05:52 PM, Dave Chinner wrote: > 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? I think I misread a review comment last posting. I will use CAP_SYS_RESROUCE on the next resend if people do not have any objections. > > Which-ever is selected, the use should be added to the list above > the definition of the capability in include/linux/capability.h... > Will do. Thanks. > Otherwise looks fine to me. > > Cheers, > > Dave. >
