| Message ID | 20211110195605.1304-1-alexandr.lobakin@intel.com (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | 0315a075f1343966ea2d9a085666a88a69ea6a3d |
| Delegated to: | Netdev Maintainers |
| Headers | show |
| Series | [v2,net] net: fix premature exit from NAPI state polling in napi_disable() | expand |
On Wed, Nov 10, 2021 at 11:56 AM Alexander Lobakin <alexandr.lobakin@intel.com> wrote: > > Commit 719c57197010 ("net: make napi_disable() symmetric with > enable") accidentally introduced a bug sometimes leading to a kernel > BUG when bringing an iface up/down under heavy traffic load. > > Prior to this commit, napi_disable() was polling n->state until > none of (NAPIF_STATE_SCHED | NAPIF_STATE_NPSVC) is set and then > always flip them. Now there's a possibility to get away with the > NAPIF_STATE_SCHE unset as 'continue' drops us to the cmpxchg() > call with an unitialized variable, rather than straight to > another round of the state check. > ... > > [0] https://lore.kernel.org/netdev/20211110191126.1214-1-alexandr.lobakin@intel.com > > Fixes: 719c57197010 ("net: make napi_disable() symmetric with enable") > Suggested-by: Eric Dumazet <edumazet@google.com> # for-loop > Signed-off-by: Alexander Lobakin <alexandr.lobakin@intel.com> > Reviewed-by: Jesse Brandeburg <jesse.brandeburg@intel.com> > --- Thanks a lot ! Reviewed-by: Eric Dumazet <edumazet@google.com>
Hello: This patch was applied to netdev/net.git (master) by Jakub Kicinski <kuba@kernel.org>: On Wed, 10 Nov 2021 20:56:05 +0100 you wrote: > Commit 719c57197010 ("net: make napi_disable() symmetric with > enable") accidentally introduced a bug sometimes leading to a kernel > BUG when bringing an iface up/down under heavy traffic load. > > Prior to this commit, napi_disable() was polling n->state until > none of (NAPIF_STATE_SCHED | NAPIF_STATE_NPSVC) is set and then > always flip them. Now there's a possibility to get away with the > NAPIF_STATE_SCHE unset as 'continue' drops us to the cmpxchg() > call with an unitialized variable, rather than straight to > another round of the state check. > > [...] Here is the summary with links: - [v2,net] net: fix premature exit from NAPI state polling in napi_disable() https://git.kernel.org/netdev/net/c/0315a075f134 You are awesome, thank you!
Alexander Lobakin [alexandr.lobakin@intel.com] wrote: > Commit 719c57197010 ("net: make napi_disable() symmetric with > enable") accidentally introduced a bug sometimes leading to a kernel > BUG when bringing an iface up/down under heavy traffic load. > > Prior to this commit, napi_disable() was polling n->state until > none of (NAPIF_STATE_SCHED | NAPIF_STATE_NPSVC) is set and then > always flip them. Now there's a possibility to get away with the > NAPIF_STATE_SCHE unset as 'continue' drops us to the cmpxchg() > call with an unitialized variable, rather than straight to > another round of the state check. Thanks. Tested v1 and it fixes the problem discussed at: https://lore.kernel.org/netdev/dc6902364a8f91c4292fe1c5e01b24be@imap.linux.ibm.com/ Sukadev
diff --git a/net/core/dev.c b/net/core/dev.c index edeb811c454e..15ac064b5562 100644 --- a/net/core/dev.c +++ b/net/core/dev.c @@ -6928,7 +6928,7 @@ void napi_disable(struct napi_struct *n) might_sleep(); set_bit(NAPI_STATE_DISABLE, &n->state); - do { + for ( ; ; ) { val = READ_ONCE(n->state); if (val & (NAPIF_STATE_SCHED | NAPIF_STATE_NPSVC)) { usleep_range(20, 200); @@ -6937,7 +6937,10 @@ void napi_disable(struct napi_struct *n) new = val | NAPIF_STATE_SCHED | NAPIF_STATE_NPSVC; new &= ~(NAPIF_STATE_THREADED | NAPIF_STATE_PREFER_BUSY_POLL); - } while (cmpxchg(&n->state, val, new) != val); + + if (cmpxchg(&n->state, val, new) == val) + break; + } hrtimer_cancel(&n->timer);
Commit 719c57197010 ("net: make napi_disable() symmetric with enable") accidentally introduced a bug sometimes leading to a kernel BUG when bringing an iface up/down under heavy traffic load. Prior to this commit, napi_disable() was polling n->state until none of (NAPIF_STATE_SCHED | NAPIF_STATE_NPSVC) is set and then always flip them. Now there's a possibility to get away with the NAPIF_STATE_SCHE unset as 'continue' drops us to the cmpxchg() call with an unitialized variable, rather than straight to another round of the state check. Error path looks like: napi_disable(): unsigned long val, new; /* new is uninitialized */ do { val = READ_ONCE(n->state); /* NAPIF_STATE_NPSVC and/or NAPIF_STATE_SCHED is set */ if (val & (NAPIF_STATE_SCHED | NAPIF_STATE_NPSVC)) { /* true */ usleep_range(20, 200); continue; /* go straight to the condition check */ } new = val | <...> } while (cmpxchg(&n->state, val, new) != val); /* state == val, cmpxchg() writes garbage */ napi_enable(): do { val = READ_ONCE(n->state); BUG_ON(!test_bit(NAPI_STATE_SCHED, &val)); /* 50/50 boom */ <...> while the typical BUG splat is like: [ 172.652461] ------------[ cut here ]------------ [ 172.652462] kernel BUG at net/core/dev.c:6937! [ 172.656914] invalid opcode: 0000 [#1] PREEMPT SMP PTI [ 172.661966] CPU: 36 PID: 2829 Comm: xdp_redirect_cp Tainted: G I 5.15.0 #42 [ 172.670222] Hardware name: Intel Corporation S2600WFT/S2600WFT, BIOS SE5C620.86B.02.01.0014.082620210524 08/26/2021 [ 172.680646] RIP: 0010:napi_enable+0x5a/0xd0 [ 172.684832] Code: 07 49 81 cc 00 01 00 00 4c 89 e2 48 89 d8 80 e6 fb f0 48 0f b1 55 10 48 39 c3 74 10 48 8b 5d 10 f6 c7 04 75 3d f6 c3 01 75 b4 <0f> 0b 5b 5d 41 5c c3 65 ff 05 b8 e5 61 53 48 c7 c6 c0 f3 34 ad 48 [ 172.703578] RSP: 0018:ffffa3c9497477a8 EFLAGS: 00010246 [ 172.708803] RAX: ffffa3c96615a014 RBX: 0000000000000000 RCX: ffff8a4b575301a0 < snip > [ 172.782403] Call Trace: [ 172.784857] <TASK> [ 172.786963] ice_up_complete+0x6f/0x210 [ice] [ 172.791349] ice_xdp+0x136/0x320 [ice] [ 172.795108] ? ice_change_mtu+0x180/0x180 [ice] [ 172.799648] dev_xdp_install+0x61/0xe0 [ 172.803401] dev_xdp_attach+0x1e0/0x550 [ 172.807240] dev_change_xdp_fd+0x1e6/0x220 [ 172.811338] do_setlink+0xee8/0x1010 [ 172.814917] rtnl_setlink+0xe5/0x170 [ 172.818499] ? bpf_lsm_binder_set_context_mgr+0x10/0x10 [ 172.823732] ? security_capable+0x36/0x50 < snip > Fix this by replacing 'do { } while (cmpxchg())' with an "infinite" for-loop with an explicit break. From v1 [0]: - just use a for-loop to simplify both the fix and the existing code (Eric). [0] https://lore.kernel.org/netdev/20211110191126.1214-1-alexandr.lobakin@intel.com Fixes: 719c57197010 ("net: make napi_disable() symmetric with enable") Suggested-by: Eric Dumazet <edumazet@google.com> # for-loop Signed-off-by: Alexander Lobakin <alexandr.lobakin@intel.com> Reviewed-by: Jesse Brandeburg <jesse.brandeburg@intel.com> --- net/core/dev.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-)