[PATCH ath-current] wifi: ath11k: fix locking problem in ath11k_dp_rx_tid_del_func()

[Nicolas Escande <nico.escande@gmail.com>]

From: Maxime Bizon <mbizon@freebox.fr>

In this function, we iterate over dp->reo_cmd_cache_flush_list using
list_for_each_entry_safe(), and for each expired entries we call
ath11k_dp_reo_cache_flush() then free the entry. As this can be called
from multiple CPU we protect for concurrent access using dp->reo_cmd_lock.

The lock is dropped to call ath11k_dp_reo_cache_flush() and taken again
before keeping iterating over the loop. That is broken.

The list_for_each_entry_safe() protects over deleting the entry being 
iterated over but does not protect for concurrent access. So another
thread might have taken the lock in between and modified the list, leading
to a crash (see bellow). 

So fix it by restarting iterating over the list from the start once the
lock is retaken.

	BUG: Unable to handle kernel paging request at virtual address 00000010ddbeef8c
	Mem abort info:
	ESR = 0x0000000096000045
	EC = 0x25: DABT (current EL), IL = 32 bits
	SET = 0, FnV = 0
	EA = 0, S1PTW = 0
	FSC = 0x05: level 1 translation fault
	Data abort info:
	ISV = 0, ISS = 0x00000045
	CM = 0, WnR = 1
	user pgtable: 4k pages, 39-bit VAs, pgdp=000000000593f000
	[00000010ddbeef8c] pgd=0000000000000000, p4d=0000000000000000, pud=0000000000000000
	Internal error: Oops: 0000000096000045 [#1] SMP
	Modules linked in: ath11k_pci XXX
	CPU: 1 PID: 1775 Comm: napi/-29 Not tainted XXXX
	Hardware name: XXXX
	pstate: 80000005 (Nzcv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
	pc : ath11k_dp_rx_tid_del_func+0x164/0x3c8
	lr : ath11k_dp_rx_tid_del_func+0x2a0/0x3c8
	sp : ffffff8020c2fb90
	x29: ffffff8020c2fb90 x28: ffffff80207ae910 x27: 0000000000000080
	x26: ffffffc00861ebe4 x25: ffffffc008cefb88 x24: ffffff800d701b2c
	x23: 00000010ddbeef84 x22: ffffff800d701448 x21: ffffff8030e22d00
	x20: ffffff800d700000 x19: 0000000000000080 x18: 0000000000000000
	x17: 0000000000000000 x16: 0000000000000000 x15: 0000000000000000
	x14: 0000000000000026 x13: ffffff801958a100 x12: 0000000000000000
	x11: 0000000000000001 x10: 0000000000000001 x9 : fffffffe0081eba0
	x8 : ffffff801cc49300 x7 : ffffffc008f87130 x6 : ffffff80207ae900
	x5 : 0000000000210d00 x4 : 0000000000000000 x3 : 0000000000000000
	x2 : 000000010024519a x1 : 00000010ddbeef84 x0 : ffffff800d701b08
	Call trace:
	ath11k_dp_rx_tid_del_func+0x164/0x3c8
	ath11k_dp_process_reo_status+0x1d4/0x2fc
	ath11k_dp_service_srng+0x334/0x338
	ath11k_pcic_ext_grp_napi_poll+0x30/0xc0
	__napi_poll+0x34/0x184
	napi_threaded_poll+0xb4/0x1d8
	kthread+0xdc/0xe0
	ret_from_fork+0x10/0x20
	Code: b946e2c0 7101001f 54fffe29 a94002a1 (f9000420)

Tested-on: QCN9074 PCI WLAN.HK.2.9.0.1-01977-QCAHKSWPL_SILICONZ-1

Fixes: d5c65159f289 ("ath11k: driver for Qualcomm IEEE 802.11ax devices")
Signed-off-by: Maxime Bizon <mbizon@freebox.fr>
Signed-off-by: Nicolas Escande <nico.escande@gmail.com>
---
 drivers/net/wireless/ath/ath11k/dp_rx.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/net/wireless/ath/ath11k/dp_rx.c b/drivers/net/wireless/ath/ath11k/dp_rx.c
index 8e2abc7b8383..b8f939f7c04b 100644
--- a/drivers/net/wireless/ath/ath11k/dp_rx.c
+++ b/drivers/net/wireless/ath/ath11k/dp_rx.c
@@ -784,6 +784,7 @@ static void ath11k_dp_rx_tid_del_func(struct ath11k_dp *dp, void *ctx,
 	dp->reo_cmd_cache_flush_count++;
 
 	/* Flush and invalidate aged REO desc from HW cache */
+retry:
 	list_for_each_entry_safe(elem, tmp, &dp->reo_cmd_cache_flush_list,
 				 list) {
 		if (dp->reo_cmd_cache_flush_count > DP_REO_DESC_FREE_THRESHOLD ||
@@ -796,6 +797,7 @@ static void ath11k_dp_rx_tid_del_func(struct ath11k_dp *dp, void *ctx,
 			ath11k_dp_reo_cache_flush(ab, &elem->data);
 			kfree(elem);
 			spin_lock_bh(&dp->reo_cmd_lock);
+			goto retry;
 		}
 	}
 	spin_unlock_bh(&dp->reo_cmd_lock);
-- 
2.55.0