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[ Upstream commit997849c4b9] Currently the freed element in bpf memory allocator may be immediately reused, for htab map the reuse will reinitialize special fields in map value (e.g., bpf_spin_lock), but lookup procedure may still access these special fields, and it may lead to hard-lockup as shown below: NMI backtrace for cpu 16 CPU: 16 PID: 2574 Comm: htab.bin Tainted: G L 6.1.0+ #1 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), RIP: 0010:queued_spin_lock_slowpath+0x283/0x2c0 ...... Call Trace: <TASK> copy_map_value_locked+0xb7/0x170 bpf_map_copy_value+0x113/0x3c0 __sys_bpf+0x1c67/0x2780 __x64_sys_bpf+0x1c/0x20 do_syscall_64+0x30/0x60 entry_SYSCALL_64_after_hwframe+0x46/0xb0 ...... </TASK> For htab map, just like the preallocated case, these is no need to initialize these special fields in map value again once these fields have been initialized. For preallocated htab map, these fields are initialized through __GFP_ZERO in bpf_map_area_alloc(), so do the similar thing for non-preallocated htab in bpf memory allocator. And there is no need to use __GFP_ZERO for per-cpu bpf memory allocator, because __alloc_percpu_gfp() does it implicitly. Fixes:0fd7c5d433("bpf: Optimize call_rcu in non-preallocated hash map.") Signed-off-by: Hou Tao <houtao1@huawei.com> Link: https://lore.kernel.org/r/20230215082132.3856544-2-houtao@huaweicloud.com Signed-off-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: Sasha Levin <sashal@kernel.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 Restructured Text 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.