Re: [PATCH 4/7] sempahore: add a helper for a concurrency limiter

[Peter Zijlstra]

On Wed, Mar 29, 2023 at 12:51:48AM -0700, Luis Chamberlain wrote:
> On Wed, Mar 29, 2023 at 09:21:12AM +0200, Peter Zijlstra wrote:
> > On Tue, Mar 28, 2023 at 10:31:46PM -0700, Luis Chamberlain wrote:
> > > While I looked at re-using the old kernel/kmod.c (now kernel/module/kmod.c)
> > > concurrency delimiter methodology for another place in the kernel Linus
> > > noted that this could be simply replaced with a sempahore [0].
> > > 
> > > So add that so we we don't re-invent the wheel and make it obvious to use.
> > > 
> > > [0] https://lore.kernel.org/all/CAHk-=whkj6=wyi201JXkw9iT_eTUTsSx+Yb9d4OgmZFjDJA18g@xxxxxxxxxxxxxx/
> > > 
> > > Suggested-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> > > Signed-off-by: Luis Chamberlain <mcgrof@xxxxxxxxxx>
> > > ---
> > >  include/linux/semaphore.h | 3 +++
> > >  1 file changed, 3 insertions(+)
> > > 
> > > diff --git a/include/linux/semaphore.h b/include/linux/semaphore.h
> > > index 6694d0019a68..2ecdffdb9814 100644
> > > --- a/include/linux/semaphore.h
> > > +++ b/include/linux/semaphore.h
> > > @@ -28,6 +28,9 @@ struct semaphore {
> > >  #define DEFINE_SEMAPHORE(name)	\
> > >  	struct semaphore name = __SEMAPHORE_INITIALIZER(name, 1)
> > >  
> > > +#define CONCURRENCY_LIMITER(name, n) \
> > > +	struct semaphore name = __SEMAPHORE_INITIALIZER(name, n)
> > > +
> > 
> > Why should this live in semaphore.h?
> 
> I have no preference, but sharing seems to have been better. Do you
> have any recommendations?

Call is DEFINE_SEMAPHORE_N() ?

Arguably DEFINE_SEMAPHORE() should have the argument, as binary
semaphores are a special case, but then we gotta go and fix up all
users.

/me git-greps a little.. Hmm, not too bad.

How's this?

---
 arch/mips/cavium-octeon/setup.c                               | 2 +-
 arch/x86/kernel/cpu/intel.c                                   | 2 +-
 drivers/firmware/efi/runtime-wrappers.c                       | 2 +-
 drivers/firmware/efi/vars.c                                   | 2 +-
 drivers/macintosh/adb.c                                       | 2 +-
 drivers/net/ethernet/broadcom/bnx2x/bnx2x_main.c              | 2 +-
 drivers/platform/x86/intel/ifs/sysfs.c                        | 2 +-
 drivers/scsi/esas2r/esas2r_ioctl.c                            | 2 +-
 drivers/staging/vc04_services/interface/vchiq_arm/vchiq_arm.c | 2 +-
 include/linux/semaphore.h                                     | 7 +++++--
 kernel/printk/printk.c                                        | 2 +-
 net/rxrpc/call_object.c                                       | 6 ++----
 12 files changed, 17 insertions(+), 16 deletions(-)

diff --git a/arch/mips/cavium-octeon/setup.c b/arch/mips/cavium-octeon/setup.c
index a71727f7a608..794b681433a7 100644
--- a/arch/mips/cavium-octeon/setup.c
+++ b/arch/mips/cavium-octeon/setup.c
@@ -72,7 +72,7 @@ extern void pci_console_init(const char *arg);
 static unsigned long long max_memory = ULLONG_MAX;
 static unsigned long long reserve_low_mem;
 
-DEFINE_SEMAPHORE(octeon_bootbus_sem);
+DEFINE_BINARY_SEMAPHORE(octeon_bootbus_sem);
 EXPORT_SYMBOL(octeon_bootbus_sem);
 
 static struct octeon_boot_descriptor *octeon_boot_desc_ptr;
diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
index 291d4167fab8..c1ace4d46c35 100644
--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -1177,7 +1177,7 @@ static const struct {
 static struct ratelimit_state bld_ratelimit;
 
 static unsigned int sysctl_sld_mitigate = 1;
-static DEFINE_SEMAPHORE(buslock_sem);
+static DEFINE_BINARY_SEMAPHORE(buslock_sem);
 
 #ifdef CONFIG_PROC_SYSCTL
 static struct ctl_table sld_sysctls[] = {
diff --git a/drivers/firmware/efi/runtime-wrappers.c b/drivers/firmware/efi/runtime-wrappers.c
index 1fba4e09cdcf..1139ad6429e7 100644
--- a/drivers/firmware/efi/runtime-wrappers.c
+++ b/drivers/firmware/efi/runtime-wrappers.c
@@ -158,7 +158,7 @@ void efi_call_virt_check_flags(unsigned long flags, const char *call)
  * none of the remaining functions are actually ever called at runtime.
  * So let's just use a single lock to serialize all Runtime Services calls.
  */
-static DEFINE_SEMAPHORE(efi_runtime_lock);
+static DEFINE_BINARY_SEMAPHORE(efi_runtime_lock);
 
 /*
  * Expose the EFI runtime lock to the UV platform
diff --git a/drivers/firmware/efi/vars.c b/drivers/firmware/efi/vars.c
index bd75b87f5fc1..09647e133c5a 100644
--- a/drivers/firmware/efi/vars.c
+++ b/drivers/firmware/efi/vars.c
@@ -21,7 +21,7 @@
 /* Private pointer to registered efivars */
 static struct efivars *__efivars;
 
-static DEFINE_SEMAPHORE(efivars_lock);
+static DEFINE_BINARY_SEMAPHORE(efivars_lock);
 
 static efi_status_t check_var_size(bool nonblocking, u32 attributes,
 				   unsigned long size)
diff --git a/drivers/macintosh/adb.c b/drivers/macintosh/adb.c
index 23bd0c77ac1a..c70b18b9f97d 100644
--- a/drivers/macintosh/adb.c
+++ b/drivers/macintosh/adb.c
@@ -80,7 +80,7 @@ static struct adb_driver *adb_controller;
 BLOCKING_NOTIFIER_HEAD(adb_client_list);
 static int adb_got_sleep;
 static int adb_inited;
-static DEFINE_SEMAPHORE(adb_probe_mutex);
+static DEFINE_BINARY_SEMAPHORE(adb_probe_mutex);
 static int sleepy_trackpad;
 static int autopoll_devs;
 int __adb_probe_sync;
diff --git a/drivers/net/ethernet/broadcom/bnx2x/bnx2x_main.c b/drivers/net/ethernet/broadcom/bnx2x/bnx2x_main.c
index 5d1e4fe335aa..0cade1fd266f 100644
--- a/drivers/net/ethernet/broadcom/bnx2x/bnx2x_main.c
+++ b/drivers/net/ethernet/broadcom/bnx2x/bnx2x_main.c
@@ -298,7 +298,7 @@ const u32 dmae_reg_go_c[] = {
 
 /* Global resources for unloading a previously loaded device */
 #define BNX2X_PREV_WAIT_NEEDED 1
-static DEFINE_SEMAPHORE(bnx2x_prev_sem);
+static DEFINE_BINARY_SEMAPHORE(bnx2x_prev_sem);
 static LIST_HEAD(bnx2x_prev_list);
 
 /* Forward declaration */
diff --git a/drivers/platform/x86/intel/ifs/sysfs.c b/drivers/platform/x86/intel/ifs/sysfs.c
index ee636a76b083..ee6782cad44f 100644
--- a/drivers/platform/x86/intel/ifs/sysfs.c
+++ b/drivers/platform/x86/intel/ifs/sysfs.c
@@ -13,7 +13,7 @@
  * Protects against simultaneous tests on multiple cores, or
  * reloading can file while a test is in progress
  */
-static DEFINE_SEMAPHORE(ifs_sem);
+static DEFINE_BINARY_SEMAPHORE(ifs_sem);
 
 /*
  * The sysfs interface to check additional details of last test
diff --git a/drivers/scsi/esas2r/esas2r_ioctl.c b/drivers/scsi/esas2r/esas2r_ioctl.c
index e003d923acbf..ca40d32181a7 100644
--- a/drivers/scsi/esas2r/esas2r_ioctl.c
+++ b/drivers/scsi/esas2r/esas2r_ioctl.c
@@ -56,7 +56,7 @@ dma_addr_t esas2r_buffered_ioctl_addr;
 u32 esas2r_buffered_ioctl_size;
 struct pci_dev *esas2r_buffered_ioctl_pcid;
 
-static DEFINE_SEMAPHORE(buffered_ioctl_semaphore);
+static DEFINE_BINARY_SEMAPHORE(buffered_ioctl_semaphore);
 typedef int (*BUFFERED_IOCTL_CALLBACK)(struct esas2r_adapter *,
 				       struct esas2r_request *,
 				       struct esas2r_sg_context *,
diff --git a/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_arm.c b/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_arm.c
index cddcd3c596c9..c7093f367f27 100644
--- a/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_arm.c
+++ b/drivers/staging/vc04_services/interface/vchiq_arm/vchiq_arm.c
@@ -149,7 +149,7 @@ static char *g_fragments_base;
 static char *g_free_fragments;
 static struct semaphore g_free_fragments_sema;
 
-static DEFINE_SEMAPHORE(g_free_fragments_mutex);
+static DEFINE_BINARY_SEMAPHORE(g_free_fragments_mutex);
 
 static int
 vchiq_blocking_bulk_transfer(struct vchiq_instance *instance, unsigned int handle, void *data,
diff --git a/include/linux/semaphore.h b/include/linux/semaphore.h
index 6694d0019a68..18894bffb3f4 100644
--- a/include/linux/semaphore.h
+++ b/include/linux/semaphore.h
@@ -25,8 +25,11 @@ struct semaphore {
 	.wait_list	= LIST_HEAD_INIT((name).wait_list),		\
 }
 
-#define DEFINE_SEMAPHORE(name)	\
-	struct semaphore name = __SEMAPHORE_INITIALIZER(name, 1)
+#define DEFINE_SEMAPHORE(_name, _n)	\
+	struct semaphore _name = __SEMAPHORE_INITIALIZER(_name, _n)
+
+#define DEFINE_BINARY_SEMAPHORE(_name)	\
+	DEFINE_SEMAPHORE(_name, 1)
 
 static inline void sema_init(struct semaphore *sem, int val)
 {
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index fd0c9f913940..a3aa21d26de2 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -89,7 +89,7 @@ static DEFINE_MUTEX(console_mutex);
  * console_sem protects updates to console->seq and console_suspended,
  * and also provides serialization for console printing.
  */
-static DEFINE_SEMAPHORE(console_sem);
+static DEFINE_BINARY_SEMAPHORE(console_sem);
 HLIST_HEAD(console_list);
 EXPORT_SYMBOL_GPL(console_list);
 DEFINE_STATIC_SRCU(console_srcu);
diff --git a/net/rxrpc/call_object.c b/net/rxrpc/call_object.c
index e9f1f49d18c2..3e5cc70884dd 100644
--- a/net/rxrpc/call_object.c
+++ b/net/rxrpc/call_object.c
@@ -40,10 +40,8 @@ const char *const rxrpc_call_completions[NR__RXRPC_CALL_COMPLETIONS] = {
 
 struct kmem_cache *rxrpc_call_jar;
 
-static struct semaphore rxrpc_call_limiter =
-	__SEMAPHORE_INITIALIZER(rxrpc_call_limiter, 1000);
-static struct semaphore rxrpc_kernel_call_limiter =
-	__SEMAPHORE_INITIALIZER(rxrpc_kernel_call_limiter, 1000);
+static DEFINE_SEMAPHORE(rxrpc_call_limiter, 1000);
+static DEFINE_SEMAPHORE(rxrpc_kernel_call_limiter, 1000);
 
 void rxrpc_poke_call(struct rxrpc_call *call, enum rxrpc_call_poke_trace what)
 {