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Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Shay Drory , Simon Horman Cc: Lukas Wunner , Bjorn Helgaas , Niklas Schnelle , netdev@vger.kernel.org, linux-rdma@vger.kernel.org, linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org, linux-pci@vger.kernel.org References: <20251202-fix_lag-v1-1-59e8177ffce0@linux.ibm.com> <99db437a-be91-4e85-a201-ec3a890900c8@linux.ibm.com> Content-Language: en-US From: Tariq Toukan In-Reply-To: <99db437a-be91-4e85-a201-ec3a890900c8@linux.ibm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 03/12/2025 23:10, Farhan Ali wrote: > > On 12/2/2025 3:12 AM, Gerd Bayer wrote: >> Clear hca_devcom_comp in device's private data after unregistering it in >> LAG teardown. Otherwise a slightly lagging second pass through >> mlx5_unload_one() might try to unregister it again and trip over >> use-after-free. >> >> On s390 almost all PCI level recovery events trigger two passes through >> mxl5_unload_one() - one through the poll_health() method and one through >> mlx5_pci_err_detected() as callback from generic PCI error recovery. >> While testing PCI error recovery paths with more kernel debug features >> enabled, this issue reproducibly led to kernel panics with the following >> call chain: >> >>   Unable to handle kernel pointer dereference in virtual kernel >> address space >>   Failing address: 6b6b6b6b6b6b6000 TEID: 6b6b6b6b6b6b6803 ESOP-2 FSI >>   Fault in home space mode while using kernel ASCE. >>   AS:00000000705c4007 R3:0000000000000024 >>   Oops: 0038 ilc:3 [#1]SMP >> >>   CPU: 14 UID: 0 PID: 156 Comm: kmcheck Kdump: loaded Not tainted >>        6.18.0-20251130.rc7.git0.16131a59cab1.300.fc43.s390x+debug #1 >> PREEMPT >> >>   Krnl PSW : 0404e00180000000 0000020fc86aa1dc >> (__lock_acquire+0x5c/0x15f0) >>              R:0 T:1 IO:0 EX:0 Key:0 M:1 W:0 P:0 AS:3 CC:2 PM:0 RI:0 EA:3 >>   Krnl GPRS: 0000000000000000 0000020f00000001 6b6b6b6b6b6b6c33 >> 0000000000000000 >>              0000000000000000 0000000000000000 0000000000000001 >> 0000000000000000 >>              0000000000000000 0000020fca28b820 0000000000000000 >> 0000010a1ced8100 >>              0000010a1ced8100 0000020fc9775068 0000018fce14f8b8 >> 0000018fce14f7f8 >>   Krnl Code: 0000020fc86aa1cc: e3b003400004        lg      %r11,832 >>              0000020fc86aa1d2: a7840211           brc >> 8,0000020fc86aa5f4 >>             *0000020fc86aa1d6: c09000df0b25       larl >> %r9,0000020fca28b820 >>             >0000020fc86aa1dc: d50790002000       clc     0(8,%r9),0(%r2) >>              0000020fc86aa1e2: a7840209           brc >> 8,0000020fc86aa5f4 >>              0000020fc86aa1e6: c0e001100401       larl >> %r14,0000020fca8aa9e8 >>              0000020fc86aa1ec: c01000e25a00       larl >> %r1,0000020fca2f55ec >>              0000020fc86aa1f2: a7eb00e8           aghi    %r14,232 >> >>   Call Trace: >>    __lock_acquire+0x5c/0x15f0 >>    lock_acquire.part.0+0xf8/0x270 >>    lock_acquire+0xb0/0x1b0 >>    down_write+0x5a/0x250 >>    mlx5_detach_device+0x42/0x110 [mlx5_core] >>    mlx5_unload_one_devl_locked+0x50/0xc0 [mlx5_core] >>    mlx5_unload_one+0x42/0x60 [mlx5_core] >>    mlx5_pci_err_detected+0x94/0x150 [mlx5_core] >>    zpci_event_attempt_error_recovery+0xcc/0x388 >> >> Fixes: 5a977b5833b7 ("net/mlx5: Lag, move devcom registration to LAG >> layer") >> Signed-off-by: Gerd Bayer >> --- >> Hi Shay et al, >> >> while checking for potential regressions by Lukas Wunner's recent work >> on pci_save/restore_state() for the recoverability of mlx5 functions I >> consistently hit this bug. (Bjorn has queued this up for 6.19, according >> to [0] and [1]) >> >> Apparently, the issue is unrelated to Lukas' work but can be reproduced >> with master. It appears to be timing-sensitive, since it shows up only >> when I use s390's debug_defconfig, but I think needs fixing anyhow, as >> timing can change for other reasons, too. >> >> I've spotted two additional places where the devcom reference is not >> cleared after calling mlx5_devcom_unregister_component() in >> drivers/net/ethernet/mellanox/mlx5/core/lib/sd.c that I have not >> addressed with a patch, since I'm unclear about how to test these >> paths. >> >> Thanks, >> Gerd >> >> [0] https://lore.kernel.org/all/cover.1760274044.git.lukas@wunner.de/ >> [1] https://lore.kernel.org/linux-pci/ >> cover.1763483367.git.lukas@wunner.de/ >> --- >>   drivers/net/ethernet/mellanox/mlx5/core/lag/lag.c | 1 + >>   1 file changed, 1 insertion(+) >> >> diff --git a/drivers/net/ethernet/mellanox/mlx5/core/lag/lag.c b/ >> drivers/net/ethernet/mellanox/mlx5/core/lag/lag.c >> index >> 3db0387bf6dcb727a65df9d0253f242554af06db..8ec04a5f434dd4f717d6d556649fcc2a584db847 100644 >> --- a/drivers/net/ethernet/mellanox/mlx5/core/lag/lag.c >> +++ b/drivers/net/ethernet/mellanox/mlx5/core/lag/lag.c >> @@ -1413,6 +1413,7 @@ static int __mlx5_lag_dev_add_mdev(struct >> mlx5_core_dev *dev) >>   static void mlx5_lag_unregister_hca_devcom_comp(struct mlx5_core_dev >> *dev) >>   { >>       mlx5_devcom_unregister_component(dev->priv.hca_devcom_comp); >> +    dev->priv.hca_devcom_comp = NULL; >>   } > > Though this fix looks correct to me in freeing hca_devcom_comp (not too > familiar with mlx5 internals), I wonder if it would be better to just > set devcom = NULL in devcom_free_comp_dev() after the kfree? This would > also take care of other places where devcom is not set to NULL? > Setting NULL after the kfree will have no impact, it won't nullify the original field, but the function parameter copy (by-value). devcom_free_comp_dev() and mlx5_devcom_unregister_component() get struct mlx5_devcom_comp_dev *devcom to work with, they can't nullify it for the caller context. > Thanks > > Farhan >