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| author | Matthew Wilcox (Oracle) <willy@infradead.org> | 2020-10-14 02:56:04 +0300 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2020-10-14 04:38:33 +0300 |
| commit | e320d3012d25b1fb5f3df4edb7bd44a1c362ec10 (patch) | |
| tree | 045231cbb1f31c38cbb22189a08d284398fc09ae /lib/Kconfig.debug | |
| parent | a9b576f7253e22528584f5aeb46edf0b6b007992 (diff) | |
| download | linux-e320d3012d25b1fb5f3df4edb7bd44a1c362ec10.tar.xz | |
mm/page_alloc.c: fix freeing non-compound pages
Here is a very rare race which leaks memory:
Page P0 is allocated to the page cache. Page P1 is free.
Thread A Thread B Thread C
find_get_entry():
xas_load() returns P0
Removes P0 from page cache
P0 finds its buddy P1
alloc_pages(GFP_KERNEL, 1) returns P0
P0 has refcount 1
page_cache_get_speculative(P0)
P0 has refcount 2
__free_pages(P0)
P0 has refcount 1
put_page(P0)
P1 is not freed
Fix this by freeing all the pages in __free_pages() that won't be freed
by the call to put_page(). It's usually not a good idea to split a page,
but this is a very unlikely scenario.
Fixes: e286781d5f2e ("mm: speculative page references")
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Mike Rapoport <rppt@linux.ibm.com>
Cc: Nick Piggin <npiggin@gmail.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200926213919.26642-1-willy@infradead.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'lib/Kconfig.debug')
| -rw-r--r-- | lib/Kconfig.debug | 9 |
1 files changed, 9 insertions, 0 deletions
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug index 0c781f912f9f..491789a793ae 100644 --- a/lib/Kconfig.debug +++ b/lib/Kconfig.debug @@ -2367,6 +2367,15 @@ config TEST_HMM If unsure, say N. +config TEST_FREE_PAGES + tristate "Test freeing pages" + help + Test that a memory leak does not occur due to a race between + freeing a block of pages and a speculative page reference. + Loading this module is safe if your kernel has the bug fixed. + If the bug is not fixed, it will leak gigabytes of memory and + probably OOM your system. + config TEST_FPU tristate "Test floating point operations in kernel space" depends on X86 && !KCOV_INSTRUMENT_ALL |