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WARN_ON() ever triggering is a kernel bug. Do not try to paper over this
fact by suggesting to the user that this is 'only' a warning, as the
following recent commit does:
commit 30e25b71e725b150585e17888b130e3324f8cf7c
Author: Jeremy Fitzhardinge <jeremy@goop.org>
Date: Fri Dec 8 02:36:24 2006 -0800
[PATCH] Fix generic WARN_ON message
A warning is a warning, not a BUG.
( it might make sense to rename BUG() to CRASH() and BUG_ON() to
CRASH_ON(), but that does not change the fact that WARN_ON()
signals a kernel bug. )
i and others objected to this change during lkml review:
http://marc.theaimsgroup.com/?l=linux-kernel&m=116115160710533&w=2
still the change slipped upstream - grumble :)
Also, use the standard "BUG: " format to make it easier to grep logs and
to make it easier to google for kernel bugs.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Cc: Jeremy Fitzhardinge <jeremy@goop.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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A warning is a warning, not a BUG.
Signed-off-by: Jeremy Fitzhardinge <jeremy@goop.org>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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This patch adds common handling for kernel BUGs, for use by architectures as
they wish. The code is derived from arch/powerpc.
The advantages of having common BUG handling are:
- consistent BUG reporting across architectures
- shared implementation of out-of-line file/line data
- implement CONFIG_DEBUG_BUGVERBOSE consistently
This means that in inline impact of BUG is just the illegal instruction
itself, which is an improvement for i386 and x86-64.
A BUG is represented in the instruction stream as an illegal instruction,
which has file/line information associated with it. This extra information is
stored in the __bug_table section in the ELF file.
When the kernel gets an illegal instruction, it first confirms it might
possibly be from a BUG (ie, in kernel mode, the right illegal instruction).
It then calls report_bug(). This searches __bug_table for a matching
instruction pointer, and if found, prints the corresponding file/line
information. If report_bug() determines that it wasn't a BUG which caused the
trap, it returns BUG_TRAP_TYPE_NONE.
Some architectures (powerpc) implement WARN using the same mechanism; if the
illegal instruction was the result of a WARN, then report_bug(Q) returns
CONFIG_DEBUG_BUGVERBOSE; otherwise it returns BUG_TRAP_TYPE_BUG.
lib/bug.c keeps a list of loaded modules which can be searched for __bug_table
entries. The architecture must call
module_bug_finalize()/module_bug_cleanup() from its corresponding
module_finalize/cleanup functions.
Unsetting CONFIG_DEBUG_BUGVERBOSE will reduce the kernel size by some amount.
At the very least, filename and line information will not be recorded for each
but, but architectures may decide to store no extra information per BUG at
all.
Unfortunately, gcc doesn't have a general way to mark an asm() as noreturn, so
architectures will generally have to include an infinite loop (or similar) in
the BUG code, so that gcc knows execution won't continue beyond that point.
gcc does have a __builtin_trap() operator which may be useful to achieve the
same effect, unfortunately it cannot be used to actually implement the BUG
itself, because there's no way to get the instruction's address for use in
generating the __bug_table entry.
[randy.dunlap@oracle.com: Handle BUG=n, GENERIC_BUG=n to prevent build errors]
[bunk@stusta.de: include/linux/bug.h must always #include <linux/module.h]
Signed-off-by: Jeremy Fitzhardinge <jeremy@goop.org>
Cc: Andi Kleen <ak@muc.de>
Cc: Hugh Dickens <hugh@veritas.com>
Cc: Michael Ellerman <michael@ellerman.id.au>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Adrian Bunk <bunk@stusta.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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In most cases the return value of WARN_ON() is ignored. If the generic
definition for the !CONFIG_BUG case is used this will result in a warning:
CC kernel/sched.o
In file included from include/linux/bio.h:25,
from include/linux/blkdev.h:14,
from kernel/sched.c:39:
include/linux/ioprio.h: In function âtask_ioprioâ:
include/linux/ioprio.h:50: warning: statement with no effect
kernel/sched.c: In function âcontext_switchâ:
kernel/sched.c:1834: warning: statement with no effect
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Cc: Jeremy Fitzhardinge <jeremy@goop.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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Tim and Ananiev report that the recent WARN_ON_ONCE changes cause increased
cache misses with the tbench workload. Apparently due to the access to the
newly-added static variable.
Rearrange the code so that we don't touch that variable unless the warning is
going to trigger.
Also rework the logic so that the static variable starts out at zero, so we
can move it into bss.
It would seem logical to mark the static variable as __read_mostly too. But
it would be wrong, because that would put it back into the vmlinux image, and
the kernel will never read from this variable in normal operation anyway.
Unless the compiler or hardware go and do some prefetching on us?
For some reason this patch shrinks softirq.o text by 40 bytes.
Cc: Tim Chen <tim.c.chen@intel.com>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: "Ananiev, Leonid I" <leonid.i.ananiev@intel.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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Letting WARN_ON/WARN_ON_ONCE return the condition means that you could do
if (WARN_ON(blah)) {
handle_impossible_case
}
Rather than
if (unlikely(blah)) {
WARN_ON(1)
handle_impossible_case
}
I checked all the newly added WARN_ON_ONCE users and none of them test the
return status so we can still change it.
[akpm@osdl.org: warning fix]
[akpm@osdl.org: build fix]
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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Introduce a new WARN_ON variant: WARN_ON_SMP(cond).
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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Add WARN_ON_ONCE(cond) to print once-per-bootup messages.
[rostedt@goodmis.org: improve code generation]
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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Signed-off-by: David Woodhouse <dwmw2@infradead.org>
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Consolidate all kernel bug printouts to begin with the "BUG: " string.
Makes it easier to find them in large bootup logs.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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Remove PAGE_BUG - repalce it with BUG and BUG_ON.
Signed-off-by: Matt Mackall <mpm@selenic.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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This patch eliminates all kernel BUGs, trims about 35k off the typical
kernel, and makes the system slightly faster.
Signed-off-by: Matt Mackall <mpm@selenic.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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Initial git repository build. I'm not bothering with the full history,
even though we have it. We can create a separate "historical" git
archive of that later if we want to, and in the meantime it's about
3.2GB when imported into git - space that would just make the early
git days unnecessarily complicated, when we don't have a lot of good
infrastructure for it.
Let it rip!
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