kernel/linux.git/ipc/sem.c, branch v6.6.132

ipc/sem: use flexible array in 'struct sem_undo'

2023-08-18T17:18:51+00:00

Turn 'semadj' in 'struct sem_undo' into a flexible array. The advantages are: - save the size of a pointer when the new undo structure is allocated - avoid some always ugly pointer arithmetic to get the address of semadj - avoid an indirection when the array is accessed While at it, use struct_size() to compute the size of the new undo structure. Link: https://lkml.kernel.org/r/1ba993d443ad7e16ac2b1902adab1f05ebdfa454.1688918791.git.christophe.jaillet@wanadoo.fr Signed-off-by: Christophe JAILLET Reviewed-by: Manfred Spraul Reviewed-by: Davidlohr Bueso Cc: Christophe JAILLET Cc: Jann Horn Signed-off-by: Andrew Morton

ipc/sem: Fix dangling sem_array access in semtimedop race

2022-12-05T18:54:44+00:00

When __do_semtimedop() goes to sleep because it has to wait for a semaphore value becoming zero or becoming bigger than some threshold, it links the on-stack sem_queue to the sem_array, then goes to sleep without holding a reference on the sem_array. When __do_semtimedop() comes back out of sleep, one of two things must happen: a) We prove that the on-stack sem_queue has been disconnected from the (possibly freed) sem_array, making it safe to return from the stack frame that the sem_queue exists in. b) We stabilize our reference to the sem_array, lock the sem_array, and detach the sem_queue from the sem_array ourselves. sem_array has RCU lifetime, so for case (b), the reference can be stabilized inside an RCU read-side critical section by locklessly checking whether the sem_queue is still connected to the sem_array. However, the current code does the lockless check on sem_queue before starting an RCU read-side critical section, so the result of the lockless check immediately becomes useless. Fix it by doing rcu_read_lock() before the lockless check. Now RCU ensures that if we observe the object being on our queue, the object can't be freed until rcu_read_unlock(). This bug is only hittable on kernel builds with full preemption support (either CONFIG_PREEMPT or PREEMPT_DYNAMIC with preempt=full). Fixes: 370b262c896e ("ipc/sem: avoid idr tree lookup for interrupted semop") Cc: stable@vger.kernel.org Signed-off-by: Jann Horn Signed-off-by: Linus Torvalds

ipc: update semtimedop() to use hrtimer

2022-05-10T01:29:20+00:00

semtimedop() should be converted to use hrtimer like it has been done for most of the system calls with timeouts. This system call already takes a struct timespec as an argument and can therefore provide finer granularity timed wait. Link: https://lkml.kernel.org/r/1651187881-2858-1-git-send-email-prakash.sangappa@oracle.com Signed-off-by: Prakash Sangappa Reviewed-by: Thomas Gleixner Reviewed-by: Davidlohr Bueso Reviewed-by: Manfred Spraul Signed-off-by: Andrew Morton

ipc/sem: remove redundant assignments

2022-05-10T01:29:20+00:00

Get rid of redundant assignments which end up in values not being read either because they are overwritten or the function ends. Reported by clang-tidy [deadcode.DeadStores] Link: https://lkml.kernel.org/r/20220409101933.207157-1-michalorzel.eng@gmail.com Signed-off-by: Michal Orzel Reviewed-by: Tom Rix Reviewed-by: Nathan Chancellor Cc: Nick Desaulniers Signed-off-by: Andrew Morton

ipc/sem: do not sleep with a spin lock held

2022-02-04T17:25:05+00:00

We can't call kvfree() with a spin lock held, so defer it. Link: https://lkml.kernel.org/r/20211223031207.556189-1-chi.minghao@zte.com.cn Fixes: fc37a3b8b438 ("[PATCH] ipc sem: use kvmalloc for sem_undo allocation") Reported-by: Zeal Robot Signed-off-by: Minghao Chi Reviewed-by: Shakeel Butt Reviewed-by: Manfred Spraul Cc: Arnd Bergmann Cc: Yang Guang Cc: Davidlohr Bueso Cc: Randy Dunlap Cc: Bhaskar Chowdhury Cc: Vasily Averin Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

ipc: remove memcg accounting for sops objects in do_semtimedop()

2021-09-14T17:22:11+00:00

Linus proposes to revert an accounting for sops objects in do_semtimedop() because it's really just a temporary buffer for a single semtimedop() system call. This object can consume up to 2 pages, syscall is sleeping one, size and duration can be controlled by user, and this allocation can be repeated by many thread at the same time. However Shakeel Butt pointed that there are much more popular objects with the same life time and similar memory consumption, the accounting of which was decided to be rejected for performance reasons. Considering at least 2 pages for task_struct and 2 pages for the kernel stack, a back of the envelope calculation gives a footprint amplification of <1.5 so this temporal buffer can be safely ignored. The factor would IMO be interesting if it was >> 2 (from the PoV of excessive (ab)use, fine-grained accounting seems to be currently unfeasible due to performance impact). Link: https://lore.kernel.org/lkml/90e254df-0dfe-f080-011e-b7c53ee7fd20@virtuozzo.com/ Fixes: 18319498fdd4 ("memcg: enable accounting of ipc resources") Signed-off-by: Vasily Averin Acked-by: Michal Hocko Reviewed-by: Michal Koutný Acked-by: Shakeel Butt Signed-off-by: Linus Torvalds

Merge tag 'for-linus' of git://git.armlinux.org.uk/~rmk/linux-arm

2021-09-09T20:25:49+00:00

Pull ARM development updates from Russell King: - Rename "mod_init" and "mod_exit" so that initcall debug output is actually useful (Randy Dunlap) - Update maintainers entries for linux-arm-kernel to indicate it is moderated for non-subscribers (Randy Dunlap) - Move install rules to arch/arm/Makefile (Masahiro Yamada) - Drop unnecessary ARCH_NR_GPIOS definition (Linus Walleij) - Don't warn about atags_to_fdt() stack size (David Heidelberg) - Speed up unaligned copy_{from,to}_kernel_nofault (Arnd Bergmann) - Get rid of set_fs() usage (Arnd Bergmann) - Remove checks for GCC prior to v4.6 (Geert Uytterhoeven) * tag 'for-linus' of git://git.armlinux.org.uk/~rmk/linux-arm: ARM: 9118/1: div64: Remove always-true __div64_const32_is_OK() duplicate ARM: 9117/1: asm-generic: div64: Remove always-true __div64_const32_is_OK() ARM: 9116/1: unified: Remove check for gcc < 4 ARM: 9110/1: oabi-compat: fix oabi epoll sparse warning ARM: 9113/1: uaccess: remove set_fs() implementation ARM: 9112/1: uaccess: add __{get,put}_kernel_nofault ARM: 9111/1: oabi-compat: rework fcntl64() emulation ARM: 9114/1: oabi-compat: rework sys_semtimedop emulation ARM: 9108/1: oabi-compat: rework epoll_wait/epoll_pwait emulation ARM: 9107/1: syscall: always store thread_info->abi_syscall ARM: 9109/1: oabi-compat: add epoll_pwait handler ARM: 9106/1: traps: use get_kernel_nofault instead of set_fs() ARM: 9115/1: mm/maccess: fix unaligned copy_{from,to}_kernel_nofault ARM: 9105/1: atags_to_fdt: don't warn about stack size ARM: 9103/1: Drop ARCH_NR_GPIOS definition ARM: 9102/1: move theinstall rules to arch/arm/Makefile ARM: 9100/1: MAINTAINERS: mark all linux-arm-kernel@infradead list as moderated ARM: 9099/1: crypto: rename 'mod_init' & 'mod_exit' functions to be module-specific

memcg: enable accounting of ipc resources

2021-09-03T16:58:12+00:00

When user creates IPC objects it forces kernel to allocate memory for these long-living objects. It makes sense to account them to restrict the host's memory consumption from inside the memcg-limited container. This patch enables accounting for IPC shared memory segments, messages semaphores and semaphore's undo lists. Link: https://lkml.kernel.org/r/d6507b06-4df6-78f8-6c54-3ae86e3b5339@virtuozzo.com Signed-off-by: Vasily Averin Reviewed-by: Shakeel Butt Cc: Alexander Viro Cc: Alexey Dobriyan Cc: Andrei Vagin Cc: Borislav Petkov Cc: Borislav Petkov Cc: Christian Brauner Cc: Dmitry Safonov <0x7f454c46@gmail.com> Cc: "Eric W. Biederman" Cc: Greg Kroah-Hartman Cc: "H. Peter Anvin" Cc: Ingo Molnar Cc: "J. Bruce Fields" Cc: Jeff Layton Cc: Jens Axboe Cc: Jiri Slaby Cc: Johannes Weiner Cc: Kirill Tkhai Cc: Michal Hocko Cc: Oleg Nesterov Cc: Roman Gushchin Cc: Serge Hallyn Cc: Tejun Heo Cc: Thomas Gleixner Cc: Vladimir Davydov Cc: Yutian Yang Cc: Zefan Li Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

ARM: 9114/1: oabi-compat: rework sys_semtimedop emulation

2021-08-20T10:39:26+00:00

sys_oabi_semtimedop() is one of the last users of set_fs() on Arm. To remove this one, expose the internal code of the actual implementation that operates on a kernel pointer and call it directly after copying. There should be no measurable impact on the normal execution of this function, and it makes the overly long function a little shorter, which may help readability. While reworking the oabi version, make it behave a little more like the native one, using kvmalloc_array() and restructure the code flow in a similar way. The naming of __do_semtimedop() is not very good, I hope someone can come up with a better name. One regression was spotted by kernel test robot and fixed before the first mailing list submission. Acked-by: Christoph Hellwig Signed-off-by: Arnd Bergmann Signed-off-by: Russell King (Oracle)

ipc/sem.c: use READ_ONCE()/WRITE_ONCE() for use_global_lock

2021-07-01T18:06:07+00:00

The patch solves three weaknesses in ipc/sem.c: 1) The initial read of use_global_lock in sem_lock() is an intentional race. KCSAN detects these accesses and prints a warning. 2) The code assumes that plain C read/writes are not mangled by the CPU or the compiler. 3) The comment it sysvipc_sem_proc_show() was hard to understand: The rest of the comments in ipc/sem.c speaks about sem_perm.lock, and suddenly this function speaks about ipc_lock_object(). To solve 1) and 2), use READ_ONCE()/WRITE_ONCE(). Plain C reads are used in code that owns sma->sem_perm.lock. The comment is updated to solve 3) [manfred@colorfullife.com: use READ_ONCE()/WRITE_ONCE() for use_global_lock] Link: https://lkml.kernel.org/r/20210627161919.3196-3-manfred@colorfullife.com Link: https://lkml.kernel.org/r/20210514175319.12195-1-manfred@colorfullife.com Signed-off-by: Manfred Spraul Reviewed-by: Paul E. McKenney Reviewed-by: Davidlohr Bueso Cc: <1vier1@web.de> Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds