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debug: Fix WARN_ON_ONCE() for modules

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Mike Galbraith reported a situation where a WARN_ON_ONCE() call in DRM
code turned into an oops.  As it turns out, WARN_ON_ONCE() seems to be
completely broken when called from a module.

The bug was introduced with the following commit:

  19d436268d ("debug: Add _ONCE() logic to report_bug()")

That commit changed WARN_ON_ONCE() to move its 'once' logic into the bug
trap handler.  It requires a writable bug table so that the BUGFLAG_DONE
bit can be written to the flags to indicate the first warning has
occurred.

The bug table was made writable for vmlinux, which relies on
vmlinux.lds.S and vmlinux.lds.h for laying out the sections.  However,
it wasn't made writable for modules, which rely on the ELF section
header flags.

Reported-by: Mike Galbraith <[email protected]>
Tested-by: Masami Hiramatsu <[email protected]>
Signed-off-by: Josh Poimboeuf <[email protected]>
Acked-by: Peter Zijlstra (Intel) <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Fixes: 19d436268d ("debug: Add _ONCE() logic to report_bug()")
Link: http://lkml.kernel.org/r/a53b04235a65478dd9afc51f5b329fdc65c84364.1500095401.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <[email protected]>
This commit is contained in:
Josh Poimboeuf 2017-07-15 00:10:58 -05:00 • committed by Ingo Molnar
commit 325cdacd03
9 changed files with 18 additions and 18 deletions
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4
arch/blackfin/include/asm/bug.h
View file

@ -21,7 +21,7 @@
#define _BUG_OR_WARN(flags) \
asm volatile( \
"1: .hword %0\n" \
" .section __bug_table,\"a\",@progbits\n" \
" .section __bug_table,\"aw\",@progbits\n" \
"2: .long 1b\n" \
" .long %1\n" \
" .short %2\n" \
@ -38,7 +38,7 @@
#define _BUG_OR_WARN(flags) \
asm volatile( \
"1: .hword %0\n" \
" .section __bug_table,\"a\",@progbits\n" \
" .section __bug_table,\"aw\",@progbits\n" \
"2: .long 1b\n" \
" .short %1\n" \
" .org 2b + %2\n" \