[PATCHv2] dma-debug: don't call __dma_entry_alloc_check_leak() under free_entries_lock

From: Sergey Senozhatsky
Date: Tue Aug 15 2023 - 22:33:51 EST

__dma_entry_alloc_check_leak() calls into printk -> serial console
output (qcom geni) and grabs port->lock under free_entries_lock
spin lock, which is a reverse locking dependency chain as qcom_geni
IRQ handler can call into dma-debug code and grab free_entries_lock
under port->lock.

Move __dma_entry_alloc_check_leak() call out of free_entries_lock
scope so that we don't acquire serial console's port->lock under it.

Trimmed-down lockdep splat:

The existing dependency chain (in reverse order) is:

-> #2 (free_entries_lock){-.-.}-{2:2}:
_raw_spin_lock_irqsave+0x60/0x80
dma_entry_alloc+0x38/0x110
debug_dma_map_page+0x60/0xf8
dma_map_page_attrs+0x1e0/0x230
dma_map_single_attrs.constprop.0+0x6c/0xc8
geni_se_rx_dma_prep+0x40/0xcc
qcom_geni_serial_isr+0x310/0x510
__handle_irq_event_percpu+0x110/0x244
handle_irq_event_percpu+0x20/0x54
handle_irq_event+0x50/0x88
handle_fasteoi_irq+0xa4/0xcc
handle_irq_desc+0x28/0x40
generic_handle_domain_irq+0x24/0x30
gic_handle_irq+0xc4/0x148
do_interrupt_handler+0xa4/0xb0
el1_interrupt+0x34/0x64
el1h_64_irq_handler+0x18/0x24
el1h_64_irq+0x64/0x68
arch_local_irq_enable+0x4/0x8
____do_softirq+0x18/0x24
...

-> #1 (&port_lock_key){-.-.}-{2:2}:
_raw_spin_lock_irqsave+0x60/0x80
qcom_geni_serial_console_write+0x184/0x1dc
console_flush_all+0x344/0x454
console_unlock+0x94/0xf0
vprintk_emit+0x238/0x24c
vprintk_default+0x3c/0x48
vprintk+0xb4/0xbc
_printk+0x68/0x90
register_console+0x230/0x38c
uart_add_one_port+0x338/0x494
qcom_geni_serial_probe+0x390/0x424
platform_probe+0x70/0xc0
really_probe+0x148/0x280
__driver_probe_device+0xfc/0x114
driver_probe_device+0x44/0x100
__device_attach_driver+0x64/0xdc
bus_for_each_drv+0xb0/0xd8
__device_attach+0xe4/0x140
device_initial_probe+0x1c/0x28
bus_probe_device+0x44/0xb0
device_add+0x538/0x668
of_device_add+0x44/0x50
of_platform_device_create_pdata+0x94/0xc8
of_platform_bus_create+0x270/0x304
of_platform_populate+0xac/0xc4
devm_of_platform_populate+0x60/0xac
geni_se_probe+0x154/0x160
platform_probe+0x70/0xc0
...

-> #0 (console_owner){-...}-{0:0}:
__lock_acquire+0xdf8/0x109c
lock_acquire+0x234/0x284
console_flush_all+0x330/0x454
console_unlock+0x94/0xf0
vprintk_emit+0x238/0x24c
vprintk_default+0x3c/0x48
vprintk+0xb4/0xbc
_printk+0x68/0x90
dma_entry_alloc+0xb4/0x110
debug_dma_map_sg+0xdc/0x2f8
__dma_map_sg_attrs+0xac/0xe4
dma_map_sgtable+0x30/0x4c
get_pages+0x1d4/0x1e4 [msm]
msm_gem_pin_pages_locked+0x38/0xac [msm]
msm_gem_pin_vma_locked+0x58/0x88 [msm]
msm_ioctl_gem_submit+0xde4/0x13ac [msm]
drm_ioctl_kernel+0xe0/0x15c
drm_ioctl+0x2e8/0x3f4
vfs_ioctl+0x30/0x50
...

Chain exists of:
console_owner --> &port_lock_key --> free_entries_lock

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(free_entries_lock);
lock(&port_lock_key);
lock(free_entries_lock);
lock(console_owner);

*** DEADLOCK ***

Call trace:
dump_backtrace+0xb4/0xf0
show_stack+0x20/0x30
dump_stack_lvl+0x60/0x84
dump_stack+0x18/0x24
print_circular_bug+0x1cc/0x234
check_noncircular+0x78/0xac
__lock_acquire+0xdf8/0x109c
lock_acquire+0x234/0x284
console_flush_all+0x330/0x454
console_unlock+0x94/0xf0
vprintk_emit+0x238/0x24c
vprintk_default+0x3c/0x48
vprintk+0xb4/0xbc
_printk+0x68/0x90
dma_entry_alloc+0xb4/0x110
debug_dma_map_sg+0xdc/0x2f8
__dma_map_sg_attrs+0xac/0xe4
dma_map_sgtable+0x30/0x4c
get_pages+0x1d4/0x1e4 [msm]
msm_gem_pin_pages_locked+0x38/0xac [msm]
msm_gem_pin_vma_locked+0x58/0x88 [msm]
msm_ioctl_gem_submit+0xde4/0x13ac [msm]
drm_ioctl_kernel+0xe0/0x15c
drm_ioctl+0x2e8/0x3f4
vfs_ioctl+0x30/0x50
...

Reported-by: Rob Clark <robdclark@xxxxxxxxxxxx>
Signed-off-by: Sergey Senozhatsky <senozhatsky@xxxxxxxxxxxx>
---
kernel/dma/debug.c | 20 +++++++++++++++-----
1 file changed, 15 insertions(+), 5 deletions(-)

diff --git a/kernel/dma/debug.c b/kernel/dma/debug.c
index f190651bcadd..06366acd27b0 100644
--- a/kernel/dma/debug.c
+++ b/kernel/dma/debug.c
@@ -637,15 +637,19 @@ static struct dma_debug_entry *__dma_entry_alloc(void)
return entry;
}

-static void __dma_entry_alloc_check_leak(void)
+/*
+ * This should be called outside of free_entries_lock scope to avoid potential
+ * deadlocks with serial consoles that use DMA.
+ */
+static void __dma_entry_alloc_check_leak(u32 nr_entries)
{
- u32 tmp = nr_total_entries % nr_prealloc_entries;
+ u32 tmp = nr_entries % nr_prealloc_entries;

/* Shout each time we tick over some multiple of the initial pool */
if (tmp < DMA_DEBUG_DYNAMIC_ENTRIES) {
pr_info("dma_debug_entry pool grown to %u (%u00%%)\n",
- nr_total_entries,
- (nr_total_entries / nr_prealloc_entries));
+ nr_entries,
+ (nr_entries / nr_prealloc_entries));
}
}

@@ -656,8 +660,10 @@ static void __dma_entry_alloc_check_leak(void)
*/
static struct dma_debug_entry *dma_entry_alloc(void)
{
+ bool alloc_check_leak = false;
struct dma_debug_entry *entry;
unsigned long flags;
+ u32 nr_entries;

spin_lock_irqsave(&free_entries_lock, flags);
if (num_free_entries == 0) {
@@ -667,13 +673,17 @@ static struct dma_debug_entry *dma_entry_alloc(void)
pr_err("debugging out of memory - disabling\n");
return NULL;
}
- __dma_entry_alloc_check_leak();
+ alloc_check_leak = true;
+ nr_entries = nr_total_entries;
}

entry = __dma_entry_alloc();

spin_unlock_irqrestore(&free_entries_lock, flags);

+ if (alloc_check_leak)
+ __dma_entry_alloc_check_leak(nr_entries);
+
#ifdef CONFIG_STACKTRACE
entry->stack_len = stack_trace_save(entry->stack_entries,
ARRAY_SIZE(entry->stack_entries),
--
2.41.0.694.ge786442a9b-goog