Hi Sascha, On Wed, Jun 19, 2024 at 11:05:28AM +0300, Kalle Valo wrote: > Sascha Hauer <s.hauer@xxxxxxxxxxxxxx> writes: > > > When an Access Point is repeatedly started it happens that the > > interrupts handler is called with priv->wdev.wiphy being NULL, but > > dereferenced in mwifiex_parse_single_response_buf() resulting in: > > > > | Unable to handle kernel NULL pointer dereference at virtual address 0000000000000140 ... > > | pc : mwifiex_get_cfp+0xd8/0x15c [mwifiex] > > | lr : mwifiex_get_cfp+0x34/0x15c [mwifiex] > > | sp : ffff8000818b3a70 > > | x29: ffff8000818b3a70 x28: ffff000006bfd8a5 x27: 0000000000000004 > > | x26: 000000000000002c x25: 0000000000001511 x24: 0000000002e86bc9 > > | x23: ffff000006bfd996 x22: 0000000000000004 x21: ffff000007bec000 > > | x20: 000000000000002c x19: 0000000000000000 x18: 0000000000000000 > > | x17: 000000040044ffff x16: 00500072b5503510 x15: ccc283740681e517 > > | x14: 0201000101006d15 x13: 0000000002e8ff43 x12: 002c01000000ffb1 > > | x11: 0100000000000000 x10: 02e8ff43002c0100 x9 : 0000ffb100100157 > > | x8 : ffff000003d20000 x7 : 00000000000002f1 x6 : 00000000ffffe124 > > | x5 : 0000000000000001 x4 : 0000000000000003 x3 : 0000000000000000 > > | x2 : 0000000000000000 x1 : 0001000000011001 x0 : 0000000000000000 > > | Call trace: > > | mwifiex_get_cfp+0xd8/0x15c [mwifiex] > > | mwifiex_parse_single_response_buf+0x1d0/0x504 [mwifiex] > > | mwifiex_handle_event_ext_scan_report+0x19c/0x2f8 [mwifiex] > > | mwifiex_process_sta_event+0x298/0xf0c [mwifiex] > > | mwifiex_process_event+0x110/0x238 [mwifiex] > > | mwifiex_main_process+0x428/0xa44 [mwifiex] > > | mwifiex_sdio_interrupt+0x64/0x12c [mwifiex_sdio] > > | process_sdio_pending_irqs+0x64/0x1b8 > > | sdio_irq_work+0x4c/0x7c > > | process_one_work+0x148/0x2a0 > > | worker_thread+0x2fc/0x40c > > | kthread+0x110/0x114 > > | ret_from_fork+0x10/0x20 > > | Code: a94153f3 a8c37bfd d50323bf d65f03c0 (f940a000) > > | ---[ end trace 0000000000000000 ]--- > > > > Fix this by adding a NULL check before dereferencing this pointer. > > > > Signed-off-by: Sascha Hauer <s.hauer@xxxxxxxxxxxxxx> > > > > --- > > > > This is the most obvious fix for this problem, but I am not sure if we > > might want to catch priv->wdev.wiphy being NULL earlier in the call > > chain. > > I haven't looked at the call but the symptoms sound like that either we > are enabling the interrupts too early or there's some kind of locking > problem so that an other cpu doesn't see the change. I agree with Kalle that there's a different underlying bug involved, and (my conclusion:) we shouldn't whack-a-mole the NULL pointer without addressing the underlying problem. Looking a bit closer (and without much other context to go on): I believe that one potential underlying problem is the complete lack of locking between cfg80211 entry points (such as mwifiex_add_virtual_intf() or mwifiex_cfg80211_change_virtual_intf()) and most stuff in the main loop (mwifiex_main_process()). The former call sites only hold the wiphy lock, and the latter tends to ... mostly not hold any locks, but rely on sequentialization with itself, and using its |main_proc_lock| for setup and teardown. It's all really bad and ready to fall down like a house of cards at any moment. Unfortunately, no one has spent time on rearchitecting this driver. So it's possible that mwifiex_process_event() (mwifiex_get_priv_by_id() / mwifiex_get_priv()) is getting a hold of a not-fully-initialized 'priv' structure. BTW, in case I can reproduce and poke at your scenario, what exactly is your test case? Are you just starting / killing / restarting hostapd in a loop? Are you running a full network manager stack that's doing something more complex (e.g., initiating scans)? Can you reproduce with some more targeted set of `iw` commands? (`iw phy ... interface add ...; iw dev ... del`) Is there anything else interesting in the dmesg logs? (Some of the worst behaviors in this driver come when we see command timeouts and mwifiex_reinit_sw(), for example.) Or barring that, can you get some kind of trace of the nl80211 command sequence, so it's clearer which command(s) are involved leading up to the problem? Brian
