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authorXuan Zhuo <xuanzhuo@linux.alibaba.com>2021-09-18 16:52:32 +0800
committerDavid S. Miller <davem@davemloft.net>2021-09-20 09:41:29 +0100
commit3765996e4f0b8a755cab215a08df744490c76052 (patch)
treead1b23ff087996af3daae2cc4221db131365eaa5 /net/core/dev.c
parente30cd812dffadc58241ae378e48728e6a161becd (diff)
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napi: fix race inside napi_enable
The process will cause napi.state to contain NAPI_STATE_SCHED and not in the poll_list, which will cause napi_disable() to get stuck. The prefix "NAPI_STATE_" is removed in the figure below, and NAPI_STATE_HASHED is ignored in napi.state. CPU0 | CPU1 | napi.state =============================================================================== napi_disable() | | SCHED | NPSVC napi_enable() | | { | | smp_mb__before_atomic(); | | clear_bit(SCHED, &n->state); | | NPSVC | napi_schedule_prep() | SCHED | NPSVC | napi_poll() | | napi_complete_done() | | { | | if (n->state & (NPSVC | | (1) | _BUSY_POLL))) | | return false; | | ................ | | } | SCHED | NPSVC | | clear_bit(NPSVC, &n->state); | | SCHED } | | | | napi_schedule_prep() | | SCHED | MISSED (2) (1) Here return direct. Because of NAPI_STATE_NPSVC exists. (2) NAPI_STATE_SCHED exists. So not add napi.poll_list to sd->poll_list Since NAPI_STATE_SCHED already exists and napi is not in the sd->poll_list queue, NAPI_STATE_SCHED cannot be cleared and will always exist. 1. This will cause this queue to no longer receive packets. 2. If you encounter napi_disable under the protection of rtnl_lock, it will cause the entire rtnl_lock to be locked, affecting the overall system. This patch uses cmpxchg to implement napi_enable(), which ensures that there will be no race due to the separation of clear two bits. Fixes: 2d8bff12699abc ("netpoll: Close race condition between poll_one_napi and napi_disable") Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com> Reviewed-by: Dust Li <dust.li@linux.alibaba.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net/core/dev.c')
-rw-r--r--net/core/dev.c16
1 files changed, 10 insertions, 6 deletions
diff --git a/net/core/dev.c b/net/core/dev.c
index 74fd402d26dd..7ee9fecd3aff 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -6923,12 +6923,16 @@ EXPORT_SYMBOL(napi_disable);
*/
void napi_enable(struct napi_struct *n)
{
- BUG_ON(!test_bit(NAPI_STATE_SCHED, &n->state));
- smp_mb__before_atomic();
- clear_bit(NAPI_STATE_SCHED, &n->state);
- clear_bit(NAPI_STATE_NPSVC, &n->state);
- if (n->dev->threaded && n->thread)
- set_bit(NAPI_STATE_THREADED, &n->state);
+ unsigned long val, new;
+
+ do {
+ val = READ_ONCE(n->state);
+ BUG_ON(!test_bit(NAPI_STATE_SCHED, &val));
+
+ new = val & ~(NAPIF_STATE_SCHED | NAPIF_STATE_NPSVC);
+ if (n->dev->threaded && n->thread)
+ new |= NAPIF_STATE_THREADED;
+ } while (cmpxchg(&n->state, val, new) != val);
}
EXPORT_SYMBOL(napi_enable);