kernel/linux.git/fs/select.c, branch v6.19.11

select: Convert to scoped user access

2025-11-04T07:28:34+00:00

Replace the open coded implementation with the scoped user access guard. No functional change intended. Signed-off-by: Thomas Gleixner Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Ingo Molnar Reviewed-by: Mathieu Desnoyers Link: https://patch.msgid.link/20251027083745.862419776@linutronix.de

fs: annotate suspected data race between poll_schedule_timeout() and pollwake()

2025-06-23T10:36:51+00:00

When running almost any select()/poll() workload intense enough, KCSAN is likely to report data races around using 'triggered' flag of 'struct poll_wqueues'. For example, running 'find /' on a tty console may trigger the following: BUG: KCSAN: data-race in poll_schedule_timeout / pollwake write to 0xffffc900030cfb90 of 4 bytes by task 97 on cpu 5: pollwake+0xd1/0x130 __wake_up_common_lock+0x7f/0xd0 n_tty_receive_buf_common+0x776/0xc30 n_tty_receive_buf2+0x3d/0x60 tty_ldisc_receive_buf+0x6b/0x100 tty_port_default_receive_buf+0x63/0xa0 flush_to_ldisc+0x169/0x3c0 process_scheduled_works+0x6fe/0xf40 worker_thread+0x53b/0x7b0 kthread+0x4f8/0x590 ret_from_fork+0x28c/0x450 ret_from_fork_asm+0x1a/0x30 read to 0xffffc900030cfb90 of 4 bytes by task 5802 on cpu 4: poll_schedule_timeout+0x96/0x160 do_sys_poll+0x966/0xb30 __se_sys_ppoll+0x1c3/0x210 __x64_sys_ppoll+0x71/0x90 x64_sys_call+0x3079/0x32b0 do_syscall_64+0xfa/0x3b0 entry_SYSCALL_64_after_hwframe+0x77/0x7f According to Jan, "there's no practical issue here because it is hard to imagine how the compiler could compile the above code using some intermediate values stored into 'triggered' or multiple fetches from 'triggered'". Nevertheless, silence KCSAN by using WRITE_ONCE() in __pollwake() and READ_ONCE() in poll_schedule_timeout(), respectively. Link: https://lore.kernel.org/linux-fsdevel/bwx72orsztfjx6aoftzzkl7wle3hi4syvusuwc7x36nw6t235e@bjwrosehblty Signed-off-by: Dmitry Antipov Link: https://lore.kernel.org/20250620063059.1800689-1-dmantipov@yandex.ru Acked-by: Marco Elver Reviewed-by: Jan Kara Signed-off-by: Christian Brauner

select: core_sys_select add unlikely branch hint on return path

2025-04-21T08:27:58+00:00

Adding an unlikely() hint on the n < 0 comparison return path improves run-time performance of the select() system call, the negative value of n is very uncommon in normal select usage. Benchmarking on an Debian based Intel(R) Core(TM) Ultra 9 285K with a 6.15-rc1 kernel built with 14.2.0 using a select of 1000 file descriptors with zero timeout shows a consistent call reduction from 258 ns down to 254 ns, which is a ~1.5% performance improvement. Results based on running 25 tests with turbo disabled (to reduce clock freq turbo changes), with 30 second run per test and comparing the number of select() calls per second. The % standard deviation of the 25 tests was 0.24%, so results are reliable. Signed-off-by: Colin Ian King Link: https://lore.kernel.org/20250414092426.53529-1-colin.i.king@gmail.com Signed-off-by: Christian Brauner

select: do_pollfd: add unlikely branch hint return path

2025-04-11T13:56:54+00:00

Adding an unlikely() hint on the fd < 0 comparison return path improves run-time performance of the poll() system call. gcov based coverage analysis based on running stress-ng and a kernel build shows that this path return path is highly unlikely. Benchmarking on an Debian based Intel(R) Core(TM) Ultra 9 285K with a 6.15-rc1 kernel and a poll of 1024 file descriptors with zero timeout shows an call reduction from 32818 ns down to 32635 ns, which is a ~0.5% performance improvement. Results based on running 25 tests with turbo disabled (to reduce clock freq turbo changes), with 30 second run per test and comparing the number of poll() calls per second. The % standard deviation of the 25 tests was 0.08%, so results are reliable. Signed-off-by: Colin Ian King Link: https://lore.kernel.org/20250409155510.577490-1-colin.i.king@gmail.com Signed-off-by: Christian Brauner

select: Fix unbalanced user_access_end()

2025-01-13T15:24:16+00:00

While working on implementing user access validation on powerpc I got the following warnings on a pmac32_defconfig build: CC fs/select.o fs/select.o: warning: objtool: sys_pselect6+0x1bc: redundant UACCESS disable fs/select.o: warning: objtool: sys_pselect6_time32+0x1bc: redundant UACCESS disable On powerpc/32s, user_read_access_begin/end() are no-ops, but the failure path has a user_access_end() instead of user_read_access_end() which means an access end without any prior access begin. Replace that user_access_end() by user_read_access_end(). Fixes: 7e71609f64ec ("pselect6() and friends: take handling the combined 6th/7th args into helper") Signed-off-by: Christophe Leroy Link: https://lore.kernel.org/r/a7139e28d767a13e667ee3c79599a8047222ef36.1736751221.git.christophe.leroy@csgroup.eu Signed-off-by: Christian Brauner

do_pollfd(): convert to CLASS(fd)

2024-11-03T06:28:07+00:00

lift setting ->revents into the caller, so that failure exits (including the early one) would be plain returns. We need the scope of our struct fd to end before the store to ->revents, since that's shared with the failure exits prior to the point where we can do fdget(). Reviewed-by: Christian Brauner Signed-off-by: Al Viro

convert do_select()

2024-11-03T06:28:07+00:00

take the logics from fdget() to fdput() into an inlined helper - with existing wait_key_set() subsumed into that. Reviewed-by: Christian Brauner Signed-off-by: Al Viro

Merge tag 'pull-stable-struct_fd' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs

2024-09-23T16:35:36+00:00

Pull 'struct fd' updates from Al Viro: "Just the 'struct fd' layout change, with conversion to accessor helpers" * tag 'pull-stable-struct_fd' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs: add struct fd constructors, get rid of __to_fd() struct fd: representation change introduce fd_file(), convert all accessors to it.

Merge branch 'address-masking'

2024-09-22T18:19:35+00:00

Merge user access fast validation using address masking. This allows architectures to optionally use a data dependent address masking model instead of a conditional branch for validating user accesses. That avoids the Spectre-v1 speculation barriers. Right now only x86-64 takes advantage of this, and not all architectures will be able to do it. It requires a guard region between the user and kernel address spaces (so that you can't overflow from one to the other), and an easy way to generate a guaranteed-to-fault address for invalid user pointers. Also note that this currently assumes that there is no difference between user read and write accesses. If extended to architectures like powerpc, we'll also need to separate out the user read-vs-write cases. * address-masking: x86: make the masked_user_access_begin() macro use its argument only once x86: do the user address masking outside the user access area x86: support user address masking instead of non-speculative conditional

Merge tag 'timers-core-2024-09-16' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2024-09-17T05:25:37+00:00

Pull timer updates from Thomas Gleixner: "Core: - Overhaul of posix-timers in preparation of removing the workaround for periodic timers which have signal delivery ignored. - Remove the historical extra jiffie in msleep() msleep() adds an extra jiffie to the timeout value to ensure minimal sleep time. The timer wheel ensures minimal sleep time since the large rewrite to a non-cascading wheel, but the extra jiffie in msleep() remained unnoticed. Remove it. - Make the timer slack handling correct for realtime tasks. The procfs interface is inconsistent and does neither reflect reality nor conforms to the man page. Show the correct 0 slack for real time tasks and enforce it at the core level instead of having inconsistent individual checks in various timer setup functions. - The usual set of updates and enhancements all over the place. Drivers: - Allow the ACPI PM timer to be turned off during suspend - No new drivers - The usual updates and enhancements in various drivers" * tag 'timers-core-2024-09-16' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (43 commits) ntp: Make sure RTC is synchronized when time goes backwards treewide: Fix wrong singular form of jiffies in comments cpu: Use already existing usleep_range() timers: Rename next_expiry_recalc() to be unique platform/x86:intel/pmc: Fix comment for the pmc_core_acpi_pm_timer_suspend_resume function clocksource/drivers/jcore: Use request_percpu_irq() clocksource/drivers/cadence-ttc: Add missing clk_disable_unprepare in ttc_setup_clockevent clocksource/drivers/asm9260: Add missing clk_disable_unprepare in asm9260_timer_init clocksource/drivers/qcom: Add missing iounmap() on errors in msm_dt_timer_init() clocksource/drivers/ingenic: Use devm_clk_get_enabled() helpers platform/x86:intel/pmc: Enable the ACPI PM Timer to be turned off when suspended clocksource: acpi_pm: Add external callback for suspend/resume clocksource/drivers/arm_arch_timer: Using for_each_available_child_of_node_scoped() dt-bindings: timer: rockchip: Add rk3576 compatible timers: Annotate possible non critical data race of next_expiry timers: Remove historical extra jiffie for timeout in msleep() hrtimer: Use and report correct timerslack values for realtime tasks hrtimer: Annotate hrtimer_cpu_base_.*_expiry() for sparse. timers: Add sparse annotation for timer_sync_wait_running(). signal: Replace BUG_ON()s ...