[PATCH] ACPI: PPTT: Fix to avoid sleep in the atomic context when PPTT is absent

* [PATCH] ACPI: PPTT: Fix to avoid sleep in the atomic context when PPTT is absent
@ 2023-03-08 11:26 Sudeep Holla
  2023-03-08 13:34 ` Pierre Gondois
  0 siblings, 1 reply; 3+ messages in thread
From: Sudeep Holla @ 2023-03-08 11:26 UTC (permalink / raw)
  To: linux-acpi, linux-kernel
  Cc: Sudeep Holla, Rafael J . Wysocki, Aishwarya TCV, Pierre Gondois

Commit 0c80f9e165f8 ("ACPI: PPTT: Leave the table mapped for the runtime usage")
enabled to map PPTT once on the first invocation of acpi_get_pptt() and
never unmapped the same allowing it to be used at runtime with out the
hassle of mapping and unmapping the table. This was needed to fetch LLC
information from the PPTT in the cpuhotplug path which is executed in
the atomic context as the acpi_get_table() might sleep waiting for a
mutex.

However it missed to handle the case when there is no PPTT on the system
which results in acpi_get_pptt() being called from all the secondary
CPUs attempting to fetch the LLC information in the atomic context
without knowing the absence of PPTT resulting in the splat like below:

 | BUG: sleeping function called from invalid context at kernel/locking/semaphore.c:164
 | in_atomic(): 1, irqs_disabled(): 1, non_block: 0, pid: 0, name: swapper/1
 | preempt_count: 1, expected: 0
 | RCU nest depth: 0, expected: 0
 | no locks held by swapper/1/0.
 | irq event stamp: 0
 | hardirqs last  enabled at (0): 0x0
 | hardirqs last disabled at (0): copy_process+0x61c/0x1b40
 | softirqs last  enabled at (0): copy_process+0x61c/0x1b40
 | softirqs last disabled at (0): 0x0
 | CPU: 1 PID: 0 Comm: swapper/1 Not tainted 6.3.0-rc1 #1
 | Call trace:
 |  dump_backtrace+0xac/0x138
 |  show_stack+0x30/0x48
 |  dump_stack_lvl+0x60/0xb0
 |  dump_stack+0x18/0x28
 |  __might_resched+0x160/0x270
 |  __might_sleep+0x58/0xb0
 |  down_timeout+0x34/0x98
 |  acpi_os_wait_semaphore+0x7c/0xc0
 |  acpi_ut_acquire_mutex+0x58/0x108
 |  acpi_get_table+0x40/0xe8
 |  acpi_get_pptt+0x48/0xa0
 |  acpi_get_cache_info+0x38/0x140
 |  init_cache_level+0xf4/0x118
 |  detect_cache_attributes+0x2e4/0x640
 |  update_siblings_masks+0x3c/0x330
 |  store_cpu_topology+0x88/0xf0
 |  secondary_start_kernel+0xd0/0x168
 |  __secondary_switched+0xb8/0xc0

Update acpi_get_pptt() to consider the fact that PPTT is once checked and
is not available on the system and return NULL avoiding any attempts to
fetch PPTT and thereby avoiding any possible sleep waiting for a mutex
in the atomic context.

Fixes: 0c80f9e165f8 ("ACPI: PPTT: Leave the table mapped for the runtime usage")
Reported-by: Aishwarya TCV <aishwarya.tcv@arm.com>
Cc: Pierre Gondois <pierre.gondois@arm.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
---
 drivers/acpi/pptt.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/acpi/pptt.c b/drivers/acpi/pptt.c
index 10975bb603fb..a35dd0e41c27 100644
--- a/drivers/acpi/pptt.c
+++ b/drivers/acpi/pptt.c
@@ -536,16 +536,19 @@ static int topology_get_acpi_cpu_tag(struct acpi_table_header *table,
 static struct acpi_table_header *acpi_get_pptt(void)
 {
 	static struct acpi_table_header *pptt;
+	static bool is_pptt_checked;
 	acpi_status status;
 
 	/*
 	 * PPTT will be used at runtime on every CPU hotplug in path, so we
 	 * don't need to call acpi_put_table() to release the table mapping.
 	 */
-	if (!pptt) {
+	if (!pptt && !is_pptt_checked) {
 		status = acpi_get_table(ACPI_SIG_PPTT, 0, &pptt);
 		if (ACPI_FAILURE(status))
 			acpi_pptt_warn_missing();
+
+		is_pptt_checked = true;
 	}
 
 	return pptt;
-- 
2.39.2


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