On Wed, Dec 23, 2020 at 3:39 PM Dmitry Kadashev <dkadashev@xxxxxxxxx> wrote: > > On Tue, Dec 22, 2020 at 11:37 PM Pavel Begunkov <asml.silence@xxxxxxxxx> wrote: > > > > On 22/12/2020 11:04, Dmitry Kadashev wrote: > > > On Tue, Dec 22, 2020 at 11:11 AM Pavel Begunkov <asml.silence@xxxxxxxxx> wrote: > > [...] > > >>> What about smaller rings? Can you check io_uring of what SQ size it can allocate? > > >>> That can be a different program, e.g. modify a bit liburing/test/nop. > > > Unfortunately I've rebooted the box I've used for tests yesterday, so I can't > > > try this there. Also I was not able to come up with an isolated reproducer for > > > this yet. > > > > > > The good news is I've found a relatively easy way to provoke this on a test VM > > > using our software. Our app runs with "admin" user perms (plus some > > > capabilities), it bumps RLIMIT_MEMLOCK to infinity on start. I've also created > > > an user called 'ioutest' to run the check for ring sizes using a different user. > > > > > > I've modified the test program slightly, to show the number of rings > > > successfully > > > created on each iteration and the actual error message (to debug a problem I was > > > having with it, but I've kept this after that). Here is the output: > > > > > > # sudo -u admin bash -c 'ulimit -a' | grep locked > > > max locked memory (kbytes, -l) 1024 > > > > > > # sudo -u ioutest bash -c 'ulimit -a' | grep locked > > > max locked memory (kbytes, -l) 1024 > > > > > > # sudo -u admin ./iou-test1 > > > Failed after 0 rings with 1024 size: Cannot allocate memory > > > Failed after 0 rings with 512 size: Cannot allocate memory > > > Failed after 0 rings with 256 size: Cannot allocate memory > > > Failed after 0 rings with 128 size: Cannot allocate memory > > > Failed after 0 rings with 64 size: Cannot allocate memory > > > Failed after 0 rings with 32 size: Cannot allocate memory > > > Failed after 0 rings with 16 size: Cannot allocate memory > > > Failed after 0 rings with 8 size: Cannot allocate memory > > > Failed after 0 rings with 4 size: Cannot allocate memory > > > Failed after 0 rings with 2 size: Cannot allocate memory > > > can't allocate 1 > > > > > > # sudo -u ioutest ./iou-test1 > > > max size 1024 > > > > Then we screw that specific user. Interestingly, if it has CAP_IPC_LOCK > > capability we don't even account locked memory. > > We do have some capabilities, but not CAP_IPC_LOCK. Ours are: > > CAP_NET_ADMIN, CAP_NET_BIND_SERVICE, CAP_SYS_RESOURCE, CAP_KILL, > CAP_DAC_READ_SEARCH. > > The latter was necessary for integration with some third-party thing that we do > not really use anymore, so we can try building without it, but it'd require some > time, mostly because I'm not sure how quickly I'd be able to provoke the issue. > > > btw, do you use registered buffers? > > No, we do not use neither registered buffers nor registered files (nor anything > else). > > Also, I just tried the test program on a real box (this time one instance of our > program is still running - can repeat the check with it dead, but I expect the > results to be pretty much the same, at least after a few more restarts). This > box runs 5.9.5. > > # sudo -u admin bash -c 'ulimit -l' > 1024 > > # sudo -u admin ./iou-test1 > Failed after 0 rings with 1024 size: Cannot allocate memory > Failed after 0 rings with 512 size: Cannot allocate memory > Failed after 0 rings with 256 size: Cannot allocate memory > Failed after 0 rings with 128 size: Cannot allocate memory > Failed after 0 rings with 64 size: Cannot allocate memory > Failed after 0 rings with 32 size: Cannot allocate memory > Failed after 0 rings with 16 size: Cannot allocate memory > Failed after 0 rings with 8 size: Cannot allocate memory > Failed after 0 rings with 4 size: Cannot allocate memory > Failed after 0 rings with 2 size: Cannot allocate memory > can't allocate 1 > > # sudo -u dmitry bash -c 'ulimit -l' > 1024 > > # sudo -u dmitry ./iou-test1 > max size 1024 Please ignore the results from the real box above (5.9.5). The memlock limit interfered with this, since our app was running in the background and it had a few rings running (most failed to be created, but not all). I'll try to make it fully stuck and repeat the test with the app dead. -- Dmitry Kadashev
