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95 lines
4.2 KiB
Diff
95 lines
4.2 KiB
Diff
From git@z Thu Jan 1 00:00:00 1970
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Subject: [PATCH v2] napi: fix race inside napi_enable
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From: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
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Date: Sat, 18 Sep 2021 16:52:32 +0800
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Message-Id: <20210918085232.71436-1-xuanzhuo@linux.alibaba.com>
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To: netdev@vger.kernel.org, linyunsheng@huawei.com
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Cc: "David S. Miller" <davem@davemloft.net>, Jakub Kicinski <kuba@kernel.org>, Eric Dumazet <edumazet@google.com>, Daniel Borkmann <daniel@iogearbox.net>, Antoine Tenart <atenart@kernel.org>, Alexander Lobakin <alobakin@pm.me>, Wei Wang <weiwan@google.com>, Taehee Yoo <ap420073@gmail.com>,Björn Töpel <bjorn@kernel.org>, Arnd Bergmann <arnd@arndb.de>, Kumar Kartikeya Dwivedi <memxor@gmail.com>, Neil Horman <nhorman@redhat.com>, Dust Li <dust.li@linux.alibaba.com>
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List-Id: <netdev.vger.kernel.org>
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MIME-Version: 1.0
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Content-Type: text/plain; charset="utf-8"
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Content-Transfer-Encoding: 7bit
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The process will cause napi.state to contain NAPI_STATE_SCHED and
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not in the poll_list, which will cause napi_disable() to get stuck.
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The prefix "NAPI_STATE_" is removed in the figure below, and
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NAPI_STATE_HASHED is ignored in napi.state.
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CPU0 | CPU1 | napi.state
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===============================================================================
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napi_disable() | | SCHED | NPSVC
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napi_enable() | |
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{ | |
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smp_mb__before_atomic(); | |
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clear_bit(SCHED, &n->state); | | NPSVC
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| napi_schedule_prep() | SCHED | NPSVC
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| napi_poll() |
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| napi_complete_done() |
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| { |
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| if (n->state & (NPSVC | | (1)
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| _BUSY_POLL))) |
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| return false; |
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| ................ |
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| } | SCHED | NPSVC
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| |
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clear_bit(NPSVC, &n->state); | | SCHED
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} | |
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napi_schedule_prep() | | SCHED | MISSED (2)
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(1) Here return direct. Because of NAPI_STATE_NPSVC exists.
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(2) NAPI_STATE_SCHED exists. So not add napi.poll_list to sd->poll_list
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Since NAPI_STATE_SCHED already exists and napi is not in the
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sd->poll_list queue, NAPI_STATE_SCHED cannot be cleared and will always
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exist.
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1. This will cause this queue to no longer receive packets.
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2. If you encounter napi_disable under the protection of rtnl_lock, it
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will cause the entire rtnl_lock to be locked, affecting the overall
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system.
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This patch uses cmpxchg to implement napi_enable(), which ensures that
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there will be no race due to the separation of clear two bits.
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Fixes: 2d8bff12699abc ("netpoll: Close race condition between poll_one_napi and napi_disable")
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Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
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Reviewed-by: Dust Li <dust.li@linux.alibaba.com>
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---
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net/core/dev.c | 16 ++++++++++------
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1 file changed, 10 insertions(+), 6 deletions(-)
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diff --git a/net/core/dev.c b/net/core/dev.c
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index 74fd402d26dd..7ee9fecd3aff 100644
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--- a/net/core/dev.c
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+++ b/net/core/dev.c
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@@ -6923,12 +6923,16 @@ EXPORT_SYMBOL(napi_disable);
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*/
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void napi_enable(struct napi_struct *n)
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{
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- BUG_ON(!test_bit(NAPI_STATE_SCHED, &n->state));
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- smp_mb__before_atomic();
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- clear_bit(NAPI_STATE_SCHED, &n->state);
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- clear_bit(NAPI_STATE_NPSVC, &n->state);
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- if (n->dev->threaded && n->thread)
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- set_bit(NAPI_STATE_THREADED, &n->state);
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+ unsigned long val, new;
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+
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+ do {
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+ val = READ_ONCE(n->state);
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+ BUG_ON(!test_bit(NAPI_STATE_SCHED, &val));
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+
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+ new = val & ~(NAPIF_STATE_SCHED | NAPIF_STATE_NPSVC);
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+ if (n->dev->threaded && n->thread)
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+ new |= NAPIF_STATE_THREADED;
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+ } while (cmpxchg(&n->state, val, new) != val);
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}
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EXPORT_SYMBOL(napi_enable);
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--
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2.31.0
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