1872b3bcd5
A memcg pointer in the per-cpu stock can be accessed by drain_all_stock() and consume_stock() in parallel, causing a potential race, which is believed to e harmless. KCSAN shows this data-race clearly in the splat below: BUG: KCSAN: data-race in drain_all_stock.part.0 / try_charge_memcg write to 0xffff88903f8b0788 of 4 bytes by task 35901 on cpu 2: try_charge_memcg (mm/memcontrol.c:2323 mm/memcontrol.c:2746) __mem_cgroup_charge (mm/memcontrol.c:7287 mm/memcontrol.c:7301) do_anonymous_page (mm/memory.c:1054 mm/memory.c:4375 mm/memory.c:4433) __handle_mm_fault (mm/memory.c:3878 mm/memory.c:5300 mm/memory.c:5441) handle_mm_fault (mm/memory.c:5606) do_user_addr_fault (arch/x86/mm/fault.c:1363) exc_page_fault (./arch/x86/include/asm/irqflags.h:37 ./arch/x86/include/asm/irqflags.h:72 arch/x86/mm/fault.c:1513 arch/x86/mm/fault.c:1563) asm_exc_page_fault (./arch/x86/include/asm/idtentry.h:623) read to 0xffff88903f8b0788 of 4 bytes by task 287 on cpu 27: drain_all_stock.part.0 (mm/memcontrol.c:2433) mem_cgroup_css_offline (mm/memcontrol.c:5398 mm/memcontrol.c:5687) css_killed_work_fn (kernel/cgroup/cgroup.c:5521 kernel/cgroup/cgroup.c:5794) process_one_work (kernel/workqueue.c:3254) worker_thread (kernel/workqueue.c:3329 kernel/workqueue.c:3416) kthread (kernel/kthread.c:388) ret_from_fork (arch/x86/kernel/process.c:147) ret_from_fork_asm (arch/x86/entry/entry_64.S:257) value changed: 0x00000014 -> 0x00000013 This happens because drain_all_stock() is reading stock->nr_pages, while consume_stock() might be updating the same address, causing a potential data-race. Make the shared addresses bulletproof regarding to reads and writes, similarly to what stock->cached_objcg and stock->cached. Annotate all accesses to stock->nr_pages with READ_ONCE()/WRITE_ONCE(). Link: https://lkml.kernel.org/r/20240501095420.679208-1-leitao@debian.org Signed-off-by: Breno Leitao <leitao@debian.org> Acked-by: Shakeel Butt <shakeel.butt@linux.dev> Reviewed-by: Roman Gushchin <roman.gushchin@linux.dev> Acked-by: Michal Hocko <mhocko@suse.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Muchun Song <songmuchun@bytedance.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.