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b=NkszQ5XeWpgnYXhdammh4vdP4eIqJy1dGFDjjg6SdCxAU21pWVceRbY7nrUQY4GYgAOyFe e34KLnq/tu6hoyO9Z8eBAV4lsRqgt2FyiP14fuM9yz1CL/Ng4Z5qvGqtyyruaYGuCkq+lp 67rnmh6tIRoxbZQM17JhtDsRPT/ysIc= X-Rspamd-Queue-Id: B5BDB8000E Authentication-Results: imf02.hostedemail.com; dkim=none ("invalid DKIM record") header.d=intel.com header.s=Intel header.b=jo+ZjegB; spf=pass (imf02.hostedemail.com: domain of ira.weiny@intel.com designates 192.55.52.151 as permitted sender) smtp.mailfrom=ira.weiny@intel.com; dmarc=pass (policy=none) header.from=intel.com; arc=reject ("signature check failed: fail, {[1] = sig:microsoft.com:reject}") X-Rspam-User: X-Rspamd-Server: rspam09 X-Stat-Signature: 1c5x6mpikfejn4pagcpw7s6s9wmpaceq X-HE-Tag: 1666397330-139831 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Fri, Oct 21, 2022 at 05:02:57PM -0700, Randy Dunlap wrote: > > > On 10/21/22 17:00, Ira Weiny wrote: > > > > > I was about to get this patch ready to send when I found this: > > > > commit b6ebaedb4cb1a18220ae626c3a9e184ee39dd248 > > Author: Andrea Arcangeli > > Date: Fri Sep 4 15:47:08 2015 -0700 > > > > userfaultfd: avoid mmap_sem read recursion in mcopy_atomic > > > > If the rwsem starves writers it wasn't strictly a bug but lockdep > > doesn't like it and this avoids depending on lowlevel implementation > > details of the lock. > > > > [akpm@linux-foundation.org: delete weird BUILD_BUG_ON()] > > Signed-off-by: Andrea Arcangeli > > Acked-by: Pavel Emelyanov > > ... > > > > So I wonder if the true fix is something to lockdep? > > > > Regardless I'll send the below patch because it will restore things to a > > working order. > > > with ; added to each + line. Indeed! I will actually compile it prior to sending an actual patch. I guess I should have done that below. :-/ Sorry. Thanks! Ira > > > But I'm CC'ing Andrea for comments. > > > > Ira > > > >> > >> Ira > >> > >> diff --git a/mm/shmem.c b/mm/shmem.c > >> index 8280a5cb48df..6c8e99bf5983 100644 > >> --- a/mm/shmem.c > >> +++ b/mm/shmem.c > >> @@ -2424,9 +2424,11 @@ int shmem_mfill_atomic_pte(struct mm_struct *dst_mm, > >> > >> if (!zeropage) { /* COPY */ > >> page_kaddr = kmap_local_folio(folio, 0); > >> + pagefault_disable() > >> ret = copy_from_user(page_kaddr, > >> (const void __user *)src_addr, > >> PAGE_SIZE); > >> + pagefault_enable() > >> kunmap_local(page_kaddr); > >> > >> /* fallback to copy_from_user outside mmap_lock */ > >> > >> > > -- > ~Randy >