On Tue, Feb 20, 2018 at 10:14 PM, Parav Pandit <parav@xxxxxxxxxxxx> wrote: > Hi Arnd Bergmann, > >> -----Original Message----- >> From: linux-rdma-owner@xxxxxxxxxxxxxxx [mailto:linux-rdma- >> owner@xxxxxxxxxxxxxxx] On Behalf Of Arnd Bergmann >> Sent: Tuesday, February 20, 2018 2:59 PM >> To: Doug Ledford <dledford@xxxxxxxxxx>; Jason Gunthorpe <jgg@xxxxxxxx> >> Cc: Arnd Bergmann <arnd@xxxxxxxx>; Leon Romanovsky >> <leonro@xxxxxxxxxxxx>; Sagi Grimberg <sagi@xxxxxxxxxxx>; Bart Van Assche >> <bart.vanassche@xxxxxxxxxxx>; linux-rdma@xxxxxxxxxxxxxxx; linux- >> kernel@xxxxxxxxxxxxxxx >> Subject: [PATCH] RDMA/core: reduce IB_POLL_BATCH constant >> >> The ib_wc structure has grown to much that putting 16 of them on the stack hits >> the warning limit for dangerous kernel stack consumption: >> >> drivers/infiniband/core/cq.c: In function 'ib_process_cq_direct': >> drivers/infiniband/core/cq.c:78:1: error: the frame size of 1032 bytes is larger >> than 1024 bytes [-Werror=frame-larger-than=] >> >> Using half that number brings us comfortably below that limit again. >> >> Fixes: 02d8883f520e ("RDMA/restrack: Add general infrastructure to track >> RDMA resources") > > It is not clear to me how above commit 02d8883f520e introduced this stack issue. My mistake, I misread the git history. I did a proper bisection now and ended up with the commit that added the IB_POLL_BACK sized array on the stack, i.e. commit 246d8b184c10 ("IB/cq: Don't force IB_POLL_DIRECT poll context for ib_process_cq_direct") > Bodong and I came across ib_wc size increase in [1] and it was fixed in [2]. > Did you hit this error after/before applying patch [2]? > > [1] https://www.spinics.net/lists/linux-rdma/msg50754.html > [2] https://patchwork.kernel.org/patch/10159623/ I did the analysis a few weeks ago when I first hit the problem but didn't send it out at the time. Today I saw the problem still persists on mainline (4.16-rc2), which does contain the patch from [2]. What I see is that 'ib_wc' is now exactly 59 bytes on 32-bit ARM, plus 5 bytes of padding, so 16 of them gets us exactly the warning limit, and then there are a few bytes for the function itself. Arnd -- 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
