Re: [PATCH] conditionalize some boring buffer_head checks

Jeff Garzik
2004-04-14T08:11:16Z

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Andrew Morton wrote:
> Andrew Morton <akpm@osdl.org> wrote:
>
>> buffer_error() was always supposed to be temporary. Once per month someone
>> reports the one in __find_get_block_slow(), but that's all. The only
>> reason for keeping it around is as a debug aid to filesystem developers.
>>
>> We could make it a no-op if !CONFIG_BUFFER_DEBUG.
>
>
> But even if we do that, the compiler cannot optimise away things like:
>
> if (atomic_read(&bh->b_count) == 0 &&
> !PageLocked(bh->b_page) &&
> !PageWriteback(bh->b_page))
> do {} while (0);

Nod.

> so if it offends you, go kill the thing outright.

If you like config variables, here's a second patch (untested but should
be obvious). As a side note, we need a Kconfig for generic debugging
options...

I would rather not kill the code in submit_bh() outright, just disable
it for non-filesystem developers.

For me, buffer_error() definition is secondary to disabling these
checks-that-noone-hits in the submit_bh() fast path.

Jeff

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===== arch/alpha/Kconfig 1.36 vs edited =====
--- 1.36/arch/alpha/Kconfig Sat Mar 20 13:29:54 2004
+++ edited/arch/alpha/Kconfig Wed Apr 14 04:03:41 2004
@@ -690,6 +690,13 @@
Say Y here only if you plan to use gdb to debug the kernel.
If you don't debug the kernel, you can say N.

+config DEBUG_BUFFERS
+ bool "Enable additional filesystem buffer_head checks"
+ depends on DEBUG_KERNEL
+ help
+ If you say Y here, additional checks are performed that aid
+ filesystem development.
+
endmenu

source "security/Kconfig"
===== arch/arm/Kconfig 1.53 vs edited =====
--- 1.53/arch/arm/Kconfig Thu Apr 8 15:41:09 2004
+++ edited/arch/arm/Kconfig Wed Apr 14 04:03:58 2004
@@ -724,6 +724,13 @@
you are concerned with the code size or don't want to see these
messages.

+config DEBUG_BUFFERS
+ bool "Enable additional filesystem buffer_head checks"
+ depends on DEBUG_KERNEL
+ help
+ If you say Y here, additional checks are performed that aid
+ filesystem development.
+
# These options are only for real kernel hackers who want to get their hands dirty.
config DEBUG_LL
bool "Kernel low-level debugging functions"
===== arch/arm26/Kconfig 1.11 vs edited =====
--- 1.11/arch/arm26/Kconfig Mon Mar 1 10:52:18 2004
+++ edited/arch/arm26/Kconfig Wed Apr 14 04:03:47 2004
@@ -316,6 +316,13 @@
Say Y here only if you plan to use gdb to debug the kernel.
If you don't debug the kernel, you can say N.

+config DEBUG_BUFFERS
+ bool "Enable additional filesystem buffer_head checks"
+ depends on DEBUG_KERNEL
+ help
+ If you say Y here, additional checks are performed that aid
+ filesystem development.
+
# These options are only for real kernel hackers who want to get their hands dirty.
config DEBUG_LL
bool "Kernel low-level debugging functions"
===== arch/i386/Kconfig 1.116 vs edited =====
--- 1.116/arch/i386/Kconfig Mon Apr 12 13:54:45 2004
+++ edited/arch/i386/Kconfig Wed Apr 14 04:04:34 2004
@@ -1286,6 +1286,13 @@
If you say Y here, various routines which may sleep will become very
noisy if they are called with a spinlock held.

+config DEBUG_BUFFERS
+ bool "Enable additional filesystem buffer_head checks"
+ depends on DEBUG_KERNEL
+ help
+ If you say Y here, additional checks are performed that aid
+ filesystem development.
+
config FRAME_POINTER
bool "Compile the kernel with frame pointers"
help
===== arch/ia64/Kconfig 1.69 vs edited =====
--- 1.69/arch/ia64/Kconfig Mon Apr 12 21:50:46 2004
+++ edited/arch/ia64/Kconfig Wed Apr 14 04:04:46 2004
@@ -503,6 +503,13 @@
Say Y here only if you plan to use gdb to debug the kernel.
If you don't debug the kernel, you can say N.

+config DEBUG_BUFFERS
+ bool "Enable additional filesystem buffer_head checks"
+ depends on DEBUG_KERNEL
+ help
+ If you say Y here, additional checks are performed that aid
+ filesystem development.
+
config SYSVIPC_COMPAT
bool
depends on COMPAT && SYSVIPC
===== arch/m68k/Kconfig 1.31 vs edited =====
--- 1.31/arch/m68k/Kconfig Thu Feb 26 06:25:58 2004
+++ edited/arch/m68k/Kconfig Wed Apr 14 04:04:50 2004
@@ -688,6 +688,13 @@
Say Y here only if you plan to use gdb to debug the kernel.
If you don't debug the kernel, you can say N.

+config DEBUG_BUFFERS
+ bool "Enable additional filesystem buffer_head checks"
+ depends on DEBUG_KERNEL
+ help
+ If you say Y here, additional checks are performed that aid
+ filesystem development.
+
endmenu

source "security/Kconfig"
===== arch/mips/Kconfig 1.24 vs edited =====
--- 1.24/arch/mips/Kconfig Fri Mar 19 01:04:54 2004
+++ edited/arch/mips/Kconfig Wed Apr 14 04:05:05 2004
@@ -1253,6 +1253,13 @@
If you say Y here, various routines which may sleep will become very
noisy if they are called with a spinlock held.

+config DEBUG_BUFFERS
+ bool "Enable additional filesystem buffer_head checks"
+ depends on DEBUG_KERNEL
+ help
+ If you say Y here, additional checks are performed that aid
+ filesystem development.
+
config RTC_DS1742
bool "DS1742 BRAM/RTC support"
depends on TOSHIBA_JMR3927 || TOSHIBA_RBTX4927
===== arch/parisc/Kconfig 1.28 vs edited =====
--- 1.28/arch/parisc/Kconfig Fri Mar 19 01:04:54 2004
+++ edited/arch/parisc/Kconfig Wed Apr 14 04:05:10 2004
@@ -222,6 +222,13 @@
Say Y here only if you plan to use gdb to debug the kernel.
If you don't debug the kernel, you can say N.

+config DEBUG_BUFFERS
+ bool "Enable additional filesystem buffer_head checks"
+ depends on DEBUG_KERNEL
+ help
+ If you say Y here, additional checks are performed that aid
+ filesystem development.
+
endmenu

source "security/Kconfig"
===== arch/ppc/Kconfig 1.57 vs edited =====
--- 1.57/arch/ppc/Kconfig Tue Mar 30 10:39:41 2004
+++ edited/arch/ppc/Kconfig Wed Apr 14 04:05:26 2004
@@ -1209,6 +1209,13 @@
debug the kernel.
If you don't debug the kernel, you can say N.

+config DEBUG_BUFFERS
+ bool "Enable additional filesystem buffer_head checks"
+ depends on DEBUG_KERNEL
+ help
+ If you say Y here, additional checks are performed that aid
+ filesystem development.
+
config BOOTX_TEXT
bool "Support for early boot text console (BootX or OpenFirmware only)"
depends PPC_OF
===== arch/ppc64/Kconfig 1.52 vs edited =====
--- 1.52/arch/ppc64/Kconfig Mon Apr 12 13:54:05 2004
+++ edited/arch/ppc64/Kconfig Wed Apr 14 04:05:16 2004
@@ -395,6 +395,13 @@
Say Y here only if you plan to use gdb to debug the kernel.
If you don't debug the kernel, you can say N.

+config DEBUG_BUFFERS
+ bool "Enable additional filesystem buffer_head checks"
+ depends on DEBUG_KERNEL
+ help
+ If you say Y here, additional checks are performed that aid
+ filesystem development.
+
endmenu

source "security/Kconfig"
===== arch/s390/Kconfig 1.25 vs edited =====
--- 1.25/arch/s390/Kconfig Fri Mar 19 01:04:54 2004
+++ edited/arch/s390/Kconfig Wed Apr 14 04:05:32 2004
@@ -397,6 +397,13 @@
Say Y here only if you plan to use gdb to debug the kernel.
If you don't debug the kernel, you can say N.

+config DEBUG_BUFFERS
+ bool "Enable additional filesystem buffer_head checks"
+ depends on DEBUG_KERNEL
+ help
+ If you say Y here, additional checks are performed that aid
+ filesystem development.
+
config DEBUG_SPINLOCK_SLEEP
bool "Sleep-inside-spinlock checking"
help
===== arch/sparc/Kconfig 1.28 vs edited =====
--- 1.28/arch/sparc/Kconfig Fri Mar 19 01:04:54 2004
+++ edited/arch/sparc/Kconfig Wed Apr 14 04:06:04 2004
@@ -448,6 +448,13 @@
of the BUG call as well as the EIP and oops trace. This aids
debugging but costs about 70-100K of memory.

+config DEBUG_BUFFERS
+ bool "Enable additional filesystem buffer_head checks"
+ depends on DEBUG_KERNEL
+ help
+ If you say Y here, additional checks are performed that aid
+ filesystem development.
+
endmenu

source "security/Kconfig"
===== arch/sparc64/Kconfig 1.50 vs edited =====
--- 1.50/arch/sparc64/Kconfig Fri Mar 19 01:04:54 2004
+++ edited/arch/sparc64/Kconfig Wed Apr 14 04:05:51 2004
@@ -679,6 +679,13 @@
Say Y here only if you plan to use gdb to debug the kernel.
If you don't debug the kernel, you can say N.

+config DEBUG_BUFFERS
+ bool "Enable additional filesystem buffer_head checks"
+ depends on DEBUG_KERNEL
+ help
+ If you say Y here, additional checks are performed that aid
+ filesystem development.
+
config STACK_DEBUG
depends on DEBUG_KERNEL
bool "Stack Overflow Detection Support"
===== arch/um/Kconfig 1.14 vs edited =====
--- 1.14/arch/um/Kconfig Mon Apr 12 13:53:57 2004
+++ edited/arch/um/Kconfig Wed Apr 14 04:06:09 2004
@@ -233,6 +233,13 @@
If you're truly short on disk space or don't expect to report any
bugs back to the UML developers, say N, otherwise say Y.

+config DEBUG_BUFFERS
+ bool "Enable additional filesystem buffer_head checks"
+ depends on DEBUG_KERNEL
+ help
+ If you say Y here, additional checks are performed that aid
+ filesystem development.
+
config FRAME_POINTER
bool
default y if DEBUG_INFO
===== arch/v850/Kconfig 1.21 vs edited =====
--- 1.21/arch/v850/Kconfig Mon Feb 16 19:42:32 2004
+++ edited/arch/v850/Kconfig Wed Apr 14 04:06:12 2004
@@ -320,6 +320,13 @@
Say Y here only if you plan to use gdb to debug the kernel.
If you don't debug the kernel, you can say N.

+config DEBUG_BUFFERS
+ bool "Enable additional filesystem buffer_head checks"
+ depends on DEBUG_KERNEL
+ help
+ If you say Y here, additional checks are performed that aid
+ filesystem development.
+
config MAGIC_SYSRQ
bool "Magic SysRq key"
depends on DEBUG_KERNEL
===== arch/x86_64/Kconfig 1.47 vs edited =====
--- 1.47/arch/x86_64/Kconfig Mon Apr 12 13:53:56 2004
+++ edited/arch/x86_64/Kconfig Wed Apr 14 04:06:16 2004
@@ -471,6 +471,13 @@
Please note that this option requires new binutils.
If you don't debug the kernel, you can say N.

+config DEBUG_BUFFERS
+ bool "Enable additional filesystem buffer_head checks"
+ depends on DEBUG_KERNEL
+ help
+ If you say Y here, additional checks are performed that aid
+ filesystem development.
+
config FRAME_POINTER
bool "Compile the kernel with frame pointers"
help
===== fs/buffer.c 1.237 vs edited =====
--- 1.237/fs/buffer.c Wed Apr 14 03:18:09 2004
+++ edited/fs/buffer.c Wed Apr 14 04:06:40 2004
@@ -2688,6 +2688,7 @@
{
struct bio *bio;

+#ifdef CONFIG_DEBUG_BUFFERS
BUG_ON(!buffer_locked(bh));
BUG_ON(!buffer_mapped(bh));
BUG_ON(!bh->b_end_io);
@@ -2698,6 +2699,7 @@
buffer_error();
if (rw == READ && buffer_dirty(bh))
buffer_error();
+#endif

/* Only clear out a write error when rewriting */
if (test_set_buffer_req(bh) && rw == WRITE)