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[ Upstream commitbced3f7db9] tcp_rtx_synack() now could be called in process context as explained in0a375c8224("tcp: tcp_rtx_synack() can be called from process context"). tcp_rtx_synack() might call tcp_make_synack(), which will touch per-CPU variables with preemption enabled. This causes the following BUG: BUG: using __this_cpu_add() in preemptible [00000000] code: ThriftIO1/5464 caller is tcp_make_synack+0x841/0xac0 Call Trace: <TASK> dump_stack_lvl+0x10d/0x1a0 check_preemption_disabled+0x104/0x110 tcp_make_synack+0x841/0xac0 tcp_v6_send_synack+0x5c/0x450 tcp_rtx_synack+0xeb/0x1f0 inet_rtx_syn_ack+0x34/0x60 tcp_check_req+0x3af/0x9e0 tcp_rcv_state_process+0x59b/0x2030 tcp_v6_do_rcv+0x5f5/0x700 release_sock+0x3a/0xf0 tcp_sendmsg+0x33/0x40 ____sys_sendmsg+0x2f2/0x490 __sys_sendmsg+0x184/0x230 do_syscall_64+0x3d/0x90 Avoid calling __TCP_INC_STATS() with will touch per-cpu variables. Use TCP_INC_STATS() which is safe to be called from context switch. Fixes:8336886f78("tcp: TCP Fast Open Server - support TFO listeners") Signed-off-by: Breno Leitao <leitao@debian.org> Reviewed-by: Eric Dumazet <edumazet@google.com> Link: https://lore.kernel.org/r/20230308190745.780221-1-leitao@debian.org Signed-off-by: Jakub Kicinski <kuba@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.