On Tue, 18 Apr 2017 20:44:30 +0300 Leon Romanovsky <leon@xxxxxxxxxx> wrote: > On Mon, Apr 17, 2017 at 01:45:24PM -0400, Chuck Lever wrote: > > > > > On Apr 15, 2017, at 5:55 AM, Leon Romanovsky <leon@xxxxxxxxxx> > > > wrote: > > > > > > On Fri, Apr 14, 2017 at 11:51:39AM -0400, Chuck Lever wrote: > > >> Howdy- > > >> > > >> I recently found a way to crash my HCA (and the whole system) > > >> using a signal on an NFS/RDMA mount point that is using FMR. > > >> I've documented the issue: > > >> > > >> https://bugzilla.linux-nfs.org/show_bug.cgi?id=305 > > >> > > >> And I have an NFS/RDMA fix I'm testing for v4.13. The fix is to > > >> prevent simultaneous calls to ib_unmap_fmr with the same FMR. > > >> > > >> While working on the fix, I've been looking for any documentation > > >> regarding serialization requirements for ib_unmap_fmr. Knut > > >> Omang pointed out to me that > > >> Documentation/infiniband/core-locking.txt makes this bold > > >> statement: > > >>> Reentrancy > > >>> > > >>> All of the methods in struct ib_device exported by a low-level > > >>> driver must be fully reentrant. The low-level driver is > > >>> required to perform all synchronization necessary to maintain > > >>> consistency, even if multiple function calls using the same > > >>> object are run simultaneously. > > >>> > > >>> The IB midlayer does not perform any serialization of function > > >>> calls. > > >>> > > >>> Because low-level drivers are reentrant, upper level protocol > > >>> consumers are not required to perform any serialization. > > >> > > >> Does this re-entrancy guarantee apply only when ib_unmap_fmr is > > >> called concurrently with unique FMRs? > > > > > > According to description, it should apply to all operations on > > > ib_device without any exclusion. > > > > > >> > > >> I've been told it is not possible for ib_unmap_fmr to detect > > >> when it has been invoked in different threads with the same > > >> FMR. > > > > > > Right, FMR management is implemented as direct writes to MPT and > > > MTT tables. HW doesn't distinguish simultaneous calls to the TPT > > > cache. > > >> but apparently the > user space equivalent does not have the same > > >> vulnerability (I did not test this assertion). > > >> > > >> I'm wondering what is proper closure here (aside from merging the > > >> NFS/RDMA fix). > > > > > > Maybe serialize unmap_frm (workqueue) from the driver side? > > > > Either correcting the documentation or a driver change is OK with > > me. > > > > Claiming that "upper level protocol consumers are not required to > > perform any serialization" seems like a stretch. > > Right, > > I added Jack to this thread, and we will need a couple of days to > think internally about possible solutions. > > Thanks > Adding Majd -Jack > > > > -- > > Chuck Lever > > > > > > -- To unsubscribe from this list: send the line "unsubscribe linux-rdma" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
