tree e5cede7ce3c4102eee46bed286a177c7f40f3727
parent fc7f27cda843ce294c71767d42b9d8abd015d7cb
author Anton Altaparmakov <anton@tuxera.com> 1710426416 +0000
committer Ingo Molnar <mingo@kernel.org> 1711101691 +0100

x86/pm: Work around false positive kmemleak report in msr_build_context()

Since:

  7ee18d677989 ("x86/power: Make restore_processor_context() sane")

kmemleak reports this issue:

  unreferenced object 0xf68241e0 (size 32):
    comm "swapper/0", pid 1, jiffies 4294668610 (age 68.432s)
    hex dump (first 32 bytes):
      00 cc cc cc 29 10 01 c0 00 00 00 00 00 00 00 00  ....)...........
      00 42 82 f6 cc cc cc cc cc cc cc cc cc cc cc cc  .B..............
    backtrace:
      [<461c1d50>] __kmem_cache_alloc_node+0x106/0x260
      [<ea65e13b>] __kmalloc+0x54/0x160
      [<c3858cd2>] msr_build_context.constprop.0+0x35/0x100
      [<46635aff>] pm_check_save_msr+0x63/0x80
      [<6b6bb938>] do_one_initcall+0x41/0x1f0
      [<3f3add60>] kernel_init_freeable+0x199/0x1e8
      [<3b538fde>] kernel_init+0x1a/0x110
      [<938ae2b2>] ret_from_fork+0x1c/0x28

Which is a false positive.

Reproducer:

  - Run rsync of whole kernel tree (multiple times if needed).
  - start a kmemleak scan
  - Note this is just an example: a lot of our internal tests hit these.

The root cause is similar to the fix in:

  b0b592cf0836 x86/pm: Fix false positive kmemleak report in msr_build_context()

ie. the alignment within the packed struct saved_context
which has everything unaligned as there is only "u16 gs;" at start of
struct where in the past there were four u16 there thus aligning
everything afterwards.  The issue is with the fact that Kmemleak only
searches for pointers that are aligned (see how pointers are scanned in
kmemleak.c) so when the struct members are not aligned it doesn't see
them.

Testing:

We run a lot of tests with our CI, and after applying this fix we do not
see any kmemleak issues any more whilst without it we see hundreds of
the above report. From a single, simple test run consisting of 416 individual test
cases on kernel 5.10 x86 with kmemleak enabled we got 20 failures due to this,
which is quite a lot. With this fix applied we get zero kmemleak related failures.

Fixes: 7ee18d677989 ("x86/power: Make restore_processor_context() sane")
Signed-off-by: Anton Altaparmakov <anton@tuxera.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: "Rafael J. Wysocki" <rafael@kernel.org>
Cc: stable@vger.kernel.org
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/r/20240314142656.17699-1-anton@tuxera.com