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d36404f21b
[ Upstream commit 62c07983bef9d3e78e71189441e1a470f0d1e653 ]
Christophe Leroy reported a ~80ms latency spike
happening at first TCP connect() time.
This is because __inet_hash_connect() uses get_random_once()
to populate a perturbation table which became quite big
after commit 4c2c8f03a5ab ("tcp: increase source port perturb table to 2^16")
get_random_once() uses DO_ONCE(), which block hard irqs for the duration
of the operation.
This patch adds DO_ONCE_SLOW() which uses a mutex instead of a spinlock
for operations where we prefer to stay in process context.
Then __inet_hash_connect() can use get_random_slow_once()
to populate its perturbation table.
Fixes: 4c2c8f03a5ab ("tcp: increase source port perturb table to 2^16")
Fixes: 190cc82489f4 ("tcp: change source port randomizarion at connect() time")
Reported-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Link: https://lore.kernel.org/netdev/CANn89iLAEYBaoYajy0Y9UmGFff5GPxDUoG-ErVB2jDdRNQ5Tug@mail.gmail.com/T/#t
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Willy Tarreau <w@1wt.eu>
Tested-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: David S. Miller <davem@davemloft.net>
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.