Messages in this thread | | | Subject | Re: [PATCH 1/2] powerpc/process: fix nested output in show_user_instructions() | From | Christophe LEROY <> | Date | Thu, 6 Sep 2018 11:04:40 +0200 |
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Le 21/08/2018 à 08:27, Michael Ellerman a écrit : > Christophe Leroy <christophe.leroy@c-s.fr> writes: > >> When two processes crash at the same time, we sometimes encounter >> nesting in the middle of a line: > > I think "interleaved" is the right word, rather than "nesting". > > They're actually (potentially) completely unrelated segfaults, that just > happen to occur at the same time. > > And in fact any output that happens simultaneously will mess things up, > it doesn't have to be another segfault.
Ok, i reworded in v2.
> >> [ 4.365317] init[1]: segfault (11) at 0 nip 0 lr 0 code 1 >> [ 4.370452] init[1]: code: XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX >> [ 4.372042] init[74]: segfault (11) at 10a74 nip 1000c198 lr 100078c8 code 1 in sh[10000000+14000] >> [ 4.386829] XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX >> [ 4.391542] init[1]: code: XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX XXXXXXXX >> [ 4.400863] init[74]: code: 90010024 bf61000c 91490a7c 3fa01002 3be00000 7d3e4b78 3bbd0c20 3b600000 >> [ 4.409867] init[74]: code: 3b9d0040 7c7fe02e 2f830000 419e0028 <89230000> 2f890000 41be001c 4b7f6e79 >> >> This patch fixes it by preparing complete lines in a buffer and >> printing it at once. >> >> Fixes: 88b0fe1757359 ("powerpc: Add show_user_instructions()") >> Cc: Murilo Opsfelder Araujo <muriloo@linux.ibm.com> >> Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr> >> --- >> arch/powerpc/kernel/process.c | 17 +++++++++-------- >> 1 file changed, 9 insertions(+), 8 deletions(-) >> >> diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c >> index 913c5725cdb2..c722ce4ca1c0 100644 >> --- a/arch/powerpc/kernel/process.c >> +++ b/arch/powerpc/kernel/process.c >> @@ -1303,32 +1303,33 @@ void show_user_instructions(struct pt_regs *regs) >> { >> unsigned long pc; >> int i; >> + char buf[96]; /* enough for 8 times 9 + 2 chars */ >> + int l = 0; > > I'm sure your math is right, but still an on-stack buffer with sprintf() > is a bit scary. > > Can you try using seq_buf instead? It is safe against overflow. > > eg, something like: > > struct seq_buf s; > char buf[96]; > > seq_buf_init(&s, buf, sizeof(buf)); > ... > seq_buf_printf(&s, ...);
Ok, I did that in v2. In the meantime I reworked the loop to avoid this uggly test against i % 8 and this duplication of the pr_info() of the code line.
Christophe
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