linux-toradex.git/mm/debug.c, branch v5.12-rc5

mm/debug: improve memcg debugging

2021-02-24T21:38:27+00:00

The memcg_data is only valid on the head page, not the tail pages.  Change
the format and location of the printout within the dump to match the other
parts of struct page better.

Link: https://lkml.kernel.org/r/20210114190200.1894484-1-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) 
Reviewed-by: Zi Yan 
Cc: Michal Hocko 
Cc: Johannes Weiner 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm: memcontrol: Use helpers to read page's memcg data

2020-12-03T02:28:05+00:00

Patch series "mm: allow mapping accounted kernel pages to userspace", v6.

Currently a non-slab kernel page which has been charged to a memory cgroup
can't be mapped to userspace.  The underlying reason is simple: PageKmemcg
flag is defined as a page type (like buddy, offline, etc), so it takes a
bit from a page->mapped counter.  Pages with a type set can't be mapped to
userspace.

But in general the kmemcg flag has nothing to do with mapping to
userspace.  It only means that the page has been accounted by the page
allocator, so it has to be properly uncharged on release.

Some bpf maps are mapping the vmalloc-based memory to userspace, and their
memory can't be accounted because of this implementation detail.

This patchset removes this limitation by moving the PageKmemcg flag into
one of the free bits of the page->mem_cgroup pointer.  Also it formalizes
accesses to the page->mem_cgroup and page->obj_cgroups using new helpers,
adds several checks and removes a couple of obsolete functions.  As the
result the code became more robust with fewer open-coded bit tricks.

This patch (of 4):

Currently there are many open-coded reads of the page->mem_cgroup pointer,
as well as a couple of read helpers, which are barely used.

It creates an obstacle on a way to reuse some bits of the pointer for
storing additional bits of information.  In fact, we already do this for
slab pages, where the last bit indicates that a pointer has an attached
vector of objcg pointers instead of a regular memcg pointer.

This commits uses 2 existing helpers and introduces a new helper to
converts all read sides to calls of these helpers:
  struct mem_cgroup *page_memcg(struct page *page);
  struct mem_cgroup *page_memcg_rcu(struct page *page);
  struct mem_cgroup *page_memcg_check(struct page *page);

page_memcg_check() is intended to be used in cases when the page can be a
slab page and have a memcg pointer pointing at objcg vector.  It does
check the lowest bit, and if set, returns NULL.  page_memcg() contains a
VM_BUG_ON_PAGE() check for the page not being a slab page.

To make sure nobody uses a direct access, struct page's
mem_cgroup/obj_cgroups is converted to unsigned long memcg_data.

Signed-off-by: Roman Gushchin 
Signed-off-by: Andrew Morton 
Signed-off-by: Alexei Starovoitov 
Reviewed-by: Shakeel Butt 
Acked-by: Johannes Weiner 
Acked-by: Michal Hocko 
Link: https://lkml.kernel.org/r/20201027001657.3398190-1-guro@fb.com
Link: https://lkml.kernel.org/r/20201027001657.3398190-2-guro@fb.com
Link: https://lore.kernel.org/bpf/20201201215900.3569844-2-guro@fb.com

mm, dump_page: rename head_mapcount() --> head_compound_mapcount()

2020-10-14T01:38:29+00:00

Rename head_pincount() --> head_compound_pincount().  These names are more
accurate (or less misleading) than the original ones.

Signed-off-by: John Hubbard 
Signed-off-by: Andrew Morton 
Cc: Qian Cai 
Cc: Matthew Wilcox 
Cc: Vlastimil Babka 
Cc: Kirill A. Shutemov 
Cc: Mike Rapoport 
Cc: William Kucharski 
Link: https://lkml.kernel.org/r/20200807183358.105097-1-jhubbard@nvidia.com
Signed-off-by: Linus Torvalds

mm/debug.c: do not dereference i_ino blindly

2020-10-14T01:38:29+00:00

__dump_page() checks i_dentry is fetchable and i_ino is earlier in the
struct than i_ino, so it ought to work fine, but it's possible that struct
randomisation has reordered i_ino after i_dentry and the pointer is just
wild enough that i_dentry is fetchable and i_ino isn't.

Also print the inode number if the dentry is invalid.

Reported-by: Vlastimil Babka 
Signed-off-by: Matthew Wilcox (Oracle) 
Signed-off-by: Andrew Morton 
Reviewed-by: John Hubbard 
Reviewed-by: Mike Rapoport 
Link: https://lkml.kernel.org/r/20200819185710.28180-1-willy@infradead.org
Signed-off-by: Linus Torvalds

mm, dump_page: do not crash with bad compound_mapcount()

2020-08-07T18:33:23+00:00

If a compound page is being split while dump_page() is being run on that
page, we can end up calling compound_mapcount() on a page that is no
longer compound.  This leads to a crash (already seen at least once in the
field), due to the VM_BUG_ON_PAGE() assertion inside compound_mapcount().

(The above is from Matthew Wilcox's analysis of Qian Cai's bug report.)

A similar problem is possible, via compound_pincount() instead of
compound_mapcount().

In order to avoid this kind of crash, make dump_page() slightly more
robust, by providing a pair of simpler routines that don't contain
assertions: head_mapcount() and head_pincount().

For debug tools, we don't want to go *too* far in this direction, but this
is a simple small fix, and the crash has already been seen, so it's a good
trade-off.

Reported-by: Qian Cai 
Suggested-by: Matthew Wilcox 
Signed-off-by: John Hubbard 
Signed-off-by: Andrew Morton 
Acked-by: Vlastimil Babka 
Cc: Kirill A. Shutemov 
Cc: Mike Rapoport 
Cc: William Kucharski 
Link: http://lkml.kernel.org/r/20200804214807.169256-1-jhubbard@nvidia.com
Signed-off-by: Linus Torvalds

mm/debug: print hashed address of struct page

2020-08-07T18:33:23+00:00

The actual address of the struct page isn't particularly helpful, while
the hashed address helps match with other messages elsewhere.  Add the PFN
that the page refers to in order to help diagnose problems where the page
is improperly aligned for the purpose.

Signed-off-by: Matthew Wilcox (Oracle) 
Signed-off-by: Andrew Morton 
Reviewed-by: John Hubbard 
Acked-by: Mike Rapoport 
Cc: "Kirill A. Shutemov" 
Cc: Vlastimil Babka 
Cc: William Kucharski 
Link: http://lkml.kernel.org/r/20200709202117.7216-7-willy@infradead.org
Signed-off-by: Linus Torvalds

mm/debug: print the inode number in dump_page

2020-08-07T18:33:23+00:00

The inode number helps correlate this page with debug messages elsewhere
in the kernel.

Signed-off-by: Matthew Wilcox (Oracle) 
Signed-off-by: Andrew Morton 
Reviewed-by: John Hubbard 
Acked-by: Mike Rapoport 
Cc: "Kirill A. Shutemov" 
Cc: Vlastimil Babka 
Cc: William Kucharski 
Link: http://lkml.kernel.org/r/20200709202117.7216-6-willy@infradead.org
Signed-off-by: Linus Torvalds

mm/debug: switch dump_page to get_kernel_nofault

2020-08-07T18:33:23+00:00

This is simpler to use than copy_from_kernel_nofault().  Also make some of
the related error messages less verbose.

Signed-off-by: Matthew Wilcox (Oracle) 
Signed-off-by: Andrew Morton 
Acked-by: Mike Rapoport 
Acked-by: Vlastimil Babka 
Cc: John Hubbard 
Cc: "Kirill A. Shutemov" 
Cc: William Kucharski 
Link: http://lkml.kernel.org/r/20200709202117.7216-5-willy@infradead.org
Signed-off-by: Linus Torvalds

mm/debug: print head flags in dump_page

2020-08-07T18:33:23+00:00

Tail page flags contain very little useful information.  Print the head
page's flags instead.  While the flags will contain "head" for tail pages,
this should not be too confusing as the previous line starts with the word
"head:" and so the flags should be interpreted as belonging to the head
page.

Signed-off-by: Matthew Wilcox (Oracle) 
Signed-off-by: Andrew Morton 
Reviewed-by: John Hubbard 
Acked-by: Mike Rapoport 
Acked-by: Vlastimil Babka 
Cc: "Kirill A. Shutemov" 
Cc: William Kucharski 
Link: http://lkml.kernel.org/r/20200709202117.7216-4-willy@infradead.org
Signed-off-by: Linus Torvalds

mm/debug: dump compound page information on a second line

2020-08-07T18:33:23+00:00

Simplify both the implementation and the output by splitting all the
compound page information onto a second line.

Reported-by: John Hubbard 
Signed-off-by: Matthew Wilcox (Oracle) 
Signed-off-by: Andrew Morton 
Tested-by: John Hubbard 
Reviewed-by: John Hubbard 
Acked-by: Mike Rapoport 
Acked-by: Vlastimil Babka 
Cc: "Kirill A. Shutemov" 
Cc: William Kucharski 
Link: http://lkml.kernel.org/r/20200709202117.7216-3-willy@infradead.org
Signed-off-by: Linus Torvalds