i40e: xsk: remove count_mask

Cited commit introduced a neat way of updating next_to_clean that does
not require boundary checks on each increment. This was done by masking
the new value with (ring length - 1) mask. Problem is that this is
applicable only for power of 2 ring sizes, for every other size this
assumption can not be made. In turn, it leads to cleaning descriptors
out of order as well as splats:

[ 1388.411915] Workqueue: events xp_release_deferred
[ 1388.411919] RIP: 0010:xp_free+0x1a/0x50
[ 1388.411921] Code: 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 f3 0f 1e fa 0f 1f 44 00 00 55 48 8b 57 70 48 8d 47 70 48 89 e5 48 39 d0 74 06 <5d> c3 cc cc cc cc 48 8b 57 60 83 82 b8 00 00 00 01 48 8b 57 60 48
[ 1388.411922] RSP: 0018:ffa0000000a83cb0 EFLAGS: 00000206
[ 1388.411923] RAX: ff11000119aa5030 RBX: 000000000000001d RCX: ff110001129b6e50
[ 1388.411924] RDX: ff11000119aa4fa0 RSI: 0000000055555554 RDI: ff11000119aa4fc0
[ 1388.411925] RBP: ffa0000000a83cb0 R08: 0000000000000000 R09: 0000000000000000
[ 1388.411926] R10: 0000000000000001 R11: 0000000000000000 R12: ff11000115829b80
[ 1388.411927] R13: 000000000000005f R14: 0000000000000000 R15: ff11000119aa4fc0
[ 1388.411928] FS:  0000000000000000(0000) GS:ff11000277e00000(0000) knlGS:0000000000000000
[ 1388.411929] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 1388.411930] CR2: 00007f1f564e6c14 CR3: 000000000783c005 CR4: 0000000000771ef0
[ 1388.411931] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 1388.411931] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 1388.411932] PKRU: 55555554
[ 1388.411933] Call Trace:
[ 1388.411934]  <IRQ>
[ 1388.411935]  ? show_regs+0x6e/0x80
[ 1388.411937]  ? watchdog_timer_fn+0x1d2/0x240
[ 1388.411939]  ? __pfx_watchdog_timer_fn+0x10/0x10
[ 1388.411941]  ? __hrtimer_run_queues+0x10e/0x290
[ 1388.411945]  ? clockevents_program_event+0xae/0x130
[ 1388.411947]  ? hrtimer_interrupt+0x105/0x240
[ 1388.411949]  ? __sysvec_apic_timer_interrupt+0x54/0x150
[ 1388.411952]  ? sysvec_apic_timer_interrupt+0x7f/0x90
[ 1388.411955]  </IRQ>
[ 1388.411955]  <TASK>
[ 1388.411956]  ? asm_sysvec_apic_timer_interrupt+0x1f/0x30
[ 1388.411958]  ? xp_free+0x1a/0x50
[ 1388.411960]  i40e_xsk_clean_rx_ring+0x5d/0x100 [i40e]
[ 1388.411968]  i40e_clean_rx_ring+0x14c/0x170 [i40e]
[ 1388.411977]  i40e_queue_pair_disable+0xda/0x260 [i40e]
[ 1388.411986]  i40e_xsk_pool_setup+0x192/0x1d0 [i40e]
[ 1388.411993]  i40e_reconfig_rss_queues+0x1f0/0x1450 [i40e]
[ 1388.412002]  xp_disable_drv_zc+0x73/0xf0
[ 1388.412004]  ? mutex_lock+0x17/0x50
[ 1388.412007]  xp_release_deferred+0x2b/0xc0
[ 1388.412010]  process_one_work+0x178/0x350
[ 1388.412011]  ? __pfx_worker_thread+0x10/0x10
[ 1388.412012]  worker_thread+0x2f7/0x420
[ 1388.412014]  ? __pfx_worker_thread+0x10/0x10
[ 1388.412015]  kthread+0xf8/0x130
[ 1388.412017]  ? __pfx_kthread+0x10/0x10
[ 1388.412019]  ret_from_fork+0x3d/0x60
[ 1388.412021]  ? __pfx_kthread+0x10/0x10
[ 1388.412023]  ret_from_fork_asm+0x1b/0x30
[ 1388.412026]  </TASK>

It comes from picking wrong ring entries when cleaning xsk buffers
during pool detach.

Remove the count_mask logic and use they boundary check when updating
next_to_process (which used to be a next_to_clean).

Fixes: c8a8ca34 ("i40e: remove unnecessary memory writes of the next to clean pointer")
Reported-by: Tushar Vyavahare <tushar.vyavahare@intel.com>
Tested-by: Tushar Vyavahare <tushar.vyavahare@intel.com>
Signed-off-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Link: https://lore.kernel.org/r/20231018163908.40841-1-maciej.fijalkowski@intel.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/intel/i40e/i40e_xsk.c

@@ -437,12 +437,12 @@ int i40e_clean_rx_irq_zc(struct i40e_ring *rx_ring, int budget)
 	unsigned int total_rx_bytes = 0, total_rx_packets = 0;
 	u16 next_to_process = rx_ring->next_to_process;
 	u16 next_to_clean = rx_ring->next_to_clean;
-	u16 count_mask = rx_ring->count - 1;
 	unsigned int xdp_res, xdp_xmit = 0;
 	struct xdp_buff *first = NULL;
+	u32 count = rx_ring->count;
 	struct bpf_prog *xdp_prog;
+	u32 entries_to_alloc;
 	bool failure = false;
-	u16 cleaned_count;
 
 	if (next_to_process != next_to_clean)
 		first = *i40e_rx_bi(rx_ring, next_to_clean);
@@ -475,7 +475,8 @@ int i40e_clean_rx_irq_zc(struct i40e_ring *rx_ring, int budget)
 						      qword);
 			bi = *i40e_rx_bi(rx_ring, next_to_process);
 			xsk_buff_free(bi);
-			next_to_process = (next_to_process + 1) & count_mask;
+			if (++next_to_process == count)
+				next_to_process = 0;
 			continue;
 		}
 
@@ -493,7 +494,8 @@ int i40e_clean_rx_irq_zc(struct i40e_ring *rx_ring, int budget)
 		else if (i40e_add_xsk_frag(rx_ring, first, bi, size))
 			break;
 
-		next_to_process = (next_to_process + 1) & count_mask;
+		if (++next_to_process == count)
+			next_to_process = 0;
 
 		if (i40e_is_non_eop(rx_ring, rx_desc))
 			continue;
@@ -513,10 +515,10 @@ int i40e_clean_rx_irq_zc(struct i40e_ring *rx_ring, int budget)
 
 	rx_ring->next_to_clean = next_to_clean;
 	rx_ring->next_to_process = next_to_process;
-	cleaned_count = (next_to_clean - rx_ring->next_to_use - 1) & count_mask;
 
-	if (cleaned_count >= I40E_RX_BUFFER_WRITE)
-		failure |= !i40e_alloc_rx_buffers_zc(rx_ring, cleaned_count);
+	entries_to_alloc = I40E_DESC_UNUSED(rx_ring);
+	if (entries_to_alloc >= I40E_RX_BUFFER_WRITE)
+		failure |= !i40e_alloc_rx_buffers_zc(rx_ring, entries_to_alloc);
 
 	i40e_finalize_xdp_rx(rx_ring, xdp_xmit);
 	i40e_update_rx_stats(rx_ring, total_rx_bytes, total_rx_packets);
@@ -752,14 +754,16 @@ int i40e_xsk_wakeup(struct net_device *dev, u32 queue_id, u32 flags)
 
 void i40e_xsk_clean_rx_ring(struct i40e_ring *rx_ring)
 {
-	u16 count_mask = rx_ring->count - 1;
 	u16 ntc = rx_ring->next_to_clean;
 	u16 ntu = rx_ring->next_to_use;
 
-	for ( ; ntc != ntu; ntc = (ntc + 1)  & count_mask) {
+	while (ntc != ntu) {
 		struct xdp_buff *rx_bi = *i40e_rx_bi(rx_ring, ntc);
 
 		xsk_buff_free(rx_bi);
+		ntc++;
+		if (ntc >= rx_ring->count)
+			ntc = 0;
 	}
 }