Eric Lee / linux-smarc-t335x-v3.2

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Commit acae05156551fd7528fbb616271e672789388e3c

Authored by Arjan van de Ven
Committed by Rusty Russell
1 parent 8c8ef42aee
Exists in master and in 4 other branches v3.2_AM335xPSP_04.06.00.11, v3.2_NEWT335xPSP_04.06.00.11, v3.2_SBC_SMARTMEN, v3.2_SMARCT335xPSP_04.06.00.11

module: create a request_module_nowait() 

There seems to be a common pattern in the kernel where drivers want to
call request_module() from inside a module_init() function. Currently
this would deadlock.

As a result, several drivers go through hoops like scheduling things via
kevent, or creating custom work queues (because kevent can deadlock on them).

This patch changes this to use a request_module_nowait() function macro instead,
which just fires the modprobe off but doesn't wait for it, and thus avoids the
original deadlock entirely.

On my laptop this already results in one less kernel thread running..

(Includes Jiri's patch to use enum umh_wait)

Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au> (bool-ified)
Cc: Jiri Slaby <jirislaby@gmail.com>

Showing 2 changed files with 14 additions and 7 deletions Side-by-side Diff

include/linux/kmod.h
Diff comments   View file @ acae051
... ... @@ -29,10 +29,15 @@
29 29 #ifdef CONFIG_MODULES
30 30 /* modprobe exit status on success, -ve on error. Return value
31 31 * usually useless though. */
32   -extern int request_module(const char * name, ...) __attribute__ ((format (printf, 1, 2)));
33   -#define try_then_request_module(x, mod...) ((x) ?: (request_module(mod), (x)))
  32 +extern int __request_module(bool wait, const char *name, ...) \
  33 + __attribute__((format(printf, 2, 3)));
  34 +#define request_module(mod...) __request_module(true, mod)
  35 +#define request_module_nowait(mod...) __request_module(false, mod)
  36 +#define try_then_request_module(x, mod...) \
  37 + ((x) ?: (__request_module(false, mod), (x)))
34 38 #else
35   -static inline int request_module(const char * name, ...) { return -ENOSYS; }
  39 +static inline int request_module(const char *name, ...) { return -ENOSYS; }
  40 +static inline int request_module_nowait(const char *name, ...) { return -ENOSYS; }
36 41 #define try_then_request_module(x, mod...) (x)
37 42 #endif
38 43  
... ... @@ -50,7 +50,8 @@
50 50 char modprobe_path[KMOD_PATH_LEN] = "/sbin/modprobe";
51 51  
52 52 /**
53   - * request_module - try to load a kernel module
  53 + * __request_module - try to load a kernel module
  54 + * @wait: wait (or not) for the operation to complete
54 55 * @fmt: printf style format string for the name of the module
55 56 * @...: arguments as specified in the format string
56 57 *
... ... @@ -63,7 +64,7 @@
63 64 * If module auto-loading support is disabled then this function
64 65 * becomes a no-operation.
65 66 */
66   -int request_module(const char *fmt, ...)
  67 +int __request_module(bool wait, const char *fmt, ...)
67 68 {
68 69 va_list args;
69 70 char module_name[MODULE_NAME_LEN];
70 71  
... ... @@ -108,11 +109,12 @@
108 109 return -ENOMEM;
109 110 }
110 111  
111   - ret = call_usermodehelper(modprobe_path, argv, envp, 1);
  112 + ret = call_usermodehelper(modprobe_path, argv, envp,
  113 + wait ? UMH_WAIT_PROC : UMH_WAIT_EXEC);
112 114 atomic_dec(&kmod_concurrent);
113 115 return ret;
114 116 }
115   -EXPORT_SYMBOL(request_module);
  117 +EXPORT_SYMBOL(__request_module);
116 118 #endif /* CONFIG_MODULES */
117 119  
118 120 struct subprocess_info {