bpf: Fix RCU stall in bpf_fd_array_map_clear()#11594
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Add a missing cond_resched() in bpf_fd_array_map_clear() loop. For PROG_ARRAY maps with many entries this loop calls prog_array_map_poke_run() per entry which can be expensive, and without yielding this can cause RCU stalls under load: rcu: INFO: rcu_preempt detected stalls on CPUs/tasks: rcu: (detected by 0, t=6502 jiffies, g=729293, q=305 ncpus=1) rcu: All QSes seen, last rcu_preempt kthread activity 6502 (4295096514-4295090012), jiffies_till_next_fqs=1, root ->qsmask 0x0 rcu: rcu_preempt kthread starved for 6502 jiffies! g729293 f0x2 RCU_GP_WAIT_FQS(5) ->state=0x0 ->cpu=0 rcu: Unless rcu_preempt kthread gets sufficient CPU time, OOM is now expected behavior. rcu: RCU grace-period kthread stack dump: task:rcu_preempt state:R running task stack:0 pid:15 tgid:15 ppid:2 task_flags:0x208040 flags:0x00004000 Call Trace: <TASK> context_switch kernel/sched/core.c:5382 [inline] __schedule+0x697/0x1430 kernel/sched/core.c:6767 __schedule_loop kernel/sched/core.c:6845 [inline] schedule+0x10a/0x3e0 kernel/sched/core.c:6860 schedule_timeout+0x145/0x2c0 kernel/time/sleep_timeout.c:99 rcu_gp_fqs_loop+0x255/0x1350 kernel/rcu/tree.c:2046 rcu_gp_kthread+0x347/0x680 kernel/rcu/tree.c:2248 kthread+0x465/0x880 kernel/kthread.c:464 ret_from_fork+0x4d/0x80 arch/x86/kernel/process.c:153 ret_from_fork_asm+0x19/0x30 arch/x86/entry/entry_64.S:245 </TASK> rcu: Stack dump where RCU GP kthread last ran: CPU: 0 UID: 0 PID: 30932 Comm: kworker/0:2 Not tainted 6.14.0-13195-g967e8def1100 #2 PREEMPT(undef) Hardware name: QEMU Ubuntu 24.04 PC v2 (i440FX + PIIX, arch_caps fix, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014 Workqueue: events prog_array_map_clear_deferred RIP: 0010:write_comp_data+0x38/0x90 kernel/kcov.c:246 Call Trace: <TASK> prog_array_map_poke_run+0x77/0x380 kernel/bpf/arraymap.c:1096 __fd_array_map_delete_elem+0x197/0x310 kernel/bpf/arraymap.c:925 bpf_fd_array_map_clear kernel/bpf/arraymap.c:1000 [inline] prog_array_map_clear_deferred+0x119/0x1b0 kernel/bpf/arraymap.c:1141 process_one_work+0x898/0x19d0 kernel/workqueue.c:3238 process_scheduled_works kernel/workqueue.c:3319 [inline] worker_thread+0x770/0x10b0 kernel/workqueue.c:3400 kthread+0x465/0x880 kernel/kthread.c:464 ret_from_fork+0x4d/0x80 arch/x86/kernel/process.c:153 ret_from_fork_asm+0x19/0x30 arch/x86/entry/entry_64.S:245 </TASK> Reviewed-by: Sun Jian <sun.jian.kdev@gmail.com> Fixes: da765a2 ("bpf: Add poke dependency tracking for prog array maps") Signed-off-by: Sechang Lim <rhkrqnwk98@gmail.com>
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Pull request for series with
subject: bpf: Fix RCU stall in bpf_fd_array_map_clear()
version: 3
url: https://patchwork.kernel.org/project/netdevbpf/list/?series=1074913