Re: [PATCH v2 05/14] mm: Introduce mf_dax_kill_procs() for fsdax case

[Dan Williams <dan.j.williams@intel.com>]

HORIGUCHI NAOYA(堀口　直也) wrote:
> On Wed, Aug 24, 2022 at 02:52:51PM -0700, Dan Williams wrote:
> > Shiyang Ruan wrote:
> > > This new function is a variant of mf_generic_kill_procs that accepts a
> > > file, offset pair instead of a struct to support multiple files sharing
> > > a DAX mapping.  It is intended to be called by the file systems as part
> > > of the memory_failure handler after the file system performed a reverse
> > > mapping from the storage address to the file and file offset.
> > > 
> > > Signed-off-by: Shiyang Ruan <ruansy.fnst@fujitsu.com>
> > > Reviewed-by: Dan Williams <dan.j.williams@intel.com>
> > > Reviewed-by: Christoph Hellwig <hch@lst.de>
> > > Reviewed-by: Darrick J. Wong <djwong@kernel.org>
> > > Reviewed-by: Miaohe Lin <linmiaohe@huawei.com>
> > > ---
> > >  include/linux/mm.h  |  2 +
> > >  mm/memory-failure.c | 96 ++++++++++++++++++++++++++++++++++++++++-----
> > >  2 files changed, 88 insertions(+), 10 deletions(-)
> > 
> > Unfortunately my test suite was only running the "non-destructive" set
> > of 'ndctl' tests which skipped some of the complex memory-failure cases.
> > Upon fixing that, bisect flags this commit as the source of the following
> > crash regression:
> 
> Thank you for testing/reporting.
> 
> > 
> >  kernel BUG at mm/memory-failure.c:310!
> >  invalid opcode: 0000 [#1] PREEMPT SMP PTI
> >  CPU: 26 PID: 1252 Comm: dax-pmd Tainted: G           OE     5.19.0-rc4+ #58
> >  Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015
> >  RIP: 0010:add_to_kill+0x304/0x400
> > [..]
> >  Call Trace:
> >   <TASK>
> >   collect_procs.part.0+0x2c8/0x470
> >   memory_failure+0x979/0xf30
> >   do_madvise.part.0.cold+0x9c/0xd3
> >   ? lock_is_held_type+0xe3/0x140
> >   ? find_held_lock+0x2b/0x80
> >   ? lock_release+0x145/0x2f0
> >   ? lock_is_held_type+0xe3/0x140
> >   ? syscall_enter_from_user_mode+0x20/0x70
> >   __x64_sys_madvise+0x56/0x70
> >   do_syscall_64+0x3a/0x80
> >   entry_SYSCALL_64_after_hwframe+0x46/0xb0
> 
> This stacktrace shows that VM_BUG_ON_VMA() in dev_pagemap_mapping_shift()
> was triggered.  I think that BUG_ON is too harsh here because address ==
> -EFAULT means that there's no mapping for the address.  The subsequent
> code considers "tk->size_shift == 0" as "no mapping" cases, so
> dev_pagemap_mapping_shift() can return 0 in such a case?
> 
> Could the following diff work for the issue?

This passes the "dax-ext4.sh" and "dax-xfs.sh" tests from the ndctl
suite.

It then fails on the "device-dax" test with this signature:

 BUG: kernel NULL pointer dereference, address: 0000000000000010
 #PF: supervisor read access in kernel mode
 #PF: error_code(0x0000) - not-present page
 PGD 8000000205073067 P4D 8000000205073067 PUD 2062b3067 PMD 0 
 Oops: 0000 [#1] PREEMPT SMP PTI
 CPU: 22 PID: 4535 Comm: device-dax Tainted: G           OE    N 6.0.0-rc2+ #59
 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015
 RIP: 0010:memory_failure+0x667/0xba0
[..]
 Call Trace:
  <TASK>
  ? _printk+0x58/0x73
  do_madvise.part.0.cold+0xaf/0xc5

Which is:

(gdb) li *(memory_failure+0x667)
0xffffffff813b7f17 is in memory_failure (mm/memory-failure.c:1933).
1928
1929            /*
1930             * Call driver's implementation to handle the memory failure, otherwise
1931             * fall back to generic handler.
1932             */
1933            if (pgmap->ops->memory_failure) {
1934                    rc = pgmap->ops->memory_failure(pgmap, pfn, 1, flags);


...I think this is just a simple matter of:

@@ -1928,7 +1930,7 @@ static int memory_failure_dev_pagemap(unsigned long pfn, int flags,
         * Call driver's implementation to handle the memory failure, otherwise
         * fall back to generic handler.
         */
-       if (pgmap->ops->memory_failure) {
+       if (pgmap->ops && pgmap->ops->memory_failure) {
                rc = pgmap->ops->memory_failure(pgmap, pfn, 1, flags);
                /*
                 * Fall back to generic handler too if operation is not


...since device-dax does not implement pagemap ops.

I will see what else pops up and make sure that this regression always
runs going forward.