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x86/dumpstack: Add log_lvl to __show_regs()
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show_trace_log_lvl() provides x86 platform-specific way to unwind
backtrace with a given log level. Unfortunately, registers dump(s) are
not printed with the same log level - instead, KERN_DEFAULT is always
used.

Arista's switches uses quite common setup with rsyslog, where only
urgent messages goes to console (console_log_level=KERN_ERR), everything
else goes into /var/log/ as the console baud-rate often is indecently
slow (9600 bps).

Backtrace dumps without registers printed have proven to be as useful as
morning standups. Furthermore, in order to introduce KERN_UNSUPPRESSED
(which I believe is still the most elegant way to fix raciness of sysrq[1])
the log level should be passed down the stack to register dumping
functions. Besides, there is a potential use-case for printing traces
with KERN_DEBUG level [2] (where registers dump shouldn't appear with
higher log level).

Add log_lvl parameter to __show_regs().
Keep the used log level intact to separate visible change.

[1]: https://lore.kernel.org/lkml/20190528002412.1625-1-dima@arista.com/
[2]: https://lore.kernel.org/linux-doc/20190724170249.9644-1-dima@arista.com/

Signed-off-by: Dmitry Safonov <dima@arista.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Petr Mladek <pmladek@suse.com>
Link: https://lkml.kernel.org/r/20200629144847.492794-3-dima@arista.com
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Dmitry Safonov authored and Thomas Gleixner committed Jul 22, 2020
1 parent fd07f80 commit 44e2153
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Showing 4 changed files with 49 additions and 43 deletions.
3 changes: 2 additions & 1 deletion arch/x86/include/asm/kdebug.h
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Original file line number Diff line number Diff line change
Expand Up @@ -36,7 +36,8 @@ extern void die(const char *, struct pt_regs *,long);
void die_addr(const char *str, struct pt_regs *regs, long err, long gp_addr);
extern int __must_check __die(const char *, struct pt_regs *, long);
extern void show_stack_regs(struct pt_regs *regs);
extern void __show_regs(struct pt_regs *regs, enum show_regs_mode);
extern void __show_regs(struct pt_regs *regs, enum show_regs_mode,
const char *log_lvl);
extern void show_iret_regs(struct pt_regs *regs, const char *log_lvl);
extern unsigned long oops_begin(void);
extern void oops_end(unsigned long, struct pt_regs *, int signr);
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9 changes: 6 additions & 3 deletions arch/x86/kernel/dumpstack.c
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Original file line number Diff line number Diff line change
Expand Up @@ -146,7 +146,7 @@ static void show_regs_if_on_stack(struct stack_info *info, struct pt_regs *regs,
* they can be printed in the right context.
*/
if (!partial && on_stack(info, regs, sizeof(*regs))) {
__show_regs(regs, SHOW_REGS_SHORT);
__show_regs(regs, SHOW_REGS_SHORT, KERN_DEFAULT);

} else if (partial && on_stack(info, (void *)regs + IRET_FRAME_OFFSET,
IRET_FRAME_SIZE)) {
Expand Down Expand Up @@ -345,7 +345,7 @@ void oops_end(unsigned long flags, struct pt_regs *regs, int signr)
oops_exit();

/* Executive summary in case the oops scrolled away */
__show_regs(&exec_summary_regs, SHOW_REGS_ALL);
__show_regs(&exec_summary_regs, SHOW_REGS_ALL, KERN_DEFAULT);

if (!signr)
return;
Expand Down Expand Up @@ -437,9 +437,12 @@ void die_addr(const char *str, struct pt_regs *regs, long err, long gp_addr)

void show_regs(struct pt_regs *regs)
{
enum show_regs_mode print_kernel_regs;

show_regs_print_info(KERN_DEFAULT);

__show_regs(regs, user_mode(regs) ? SHOW_REGS_USER : SHOW_REGS_ALL);
print_kernel_regs = user_mode(regs) ? SHOW_REGS_USER : SHOW_REGS_ALL;
__show_regs(regs, print_kernel_regs, KERN_DEFAULT);

/*
* When in-kernel, we also print out the stack at the time of the fault..
Expand Down
29 changes: 15 additions & 14 deletions arch/x86/kernel/process_32.c
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Original file line number Diff line number Diff line change
Expand Up @@ -56,7 +56,8 @@

#include "process.h"

void __show_regs(struct pt_regs *regs, enum show_regs_mode mode)
void __show_regs(struct pt_regs *regs, enum show_regs_mode mode,
const char *log_lvl)
{
unsigned long cr0 = 0L, cr2 = 0L, cr3 = 0L, cr4 = 0L;
unsigned long d0, d1, d2, d3, d6, d7;
Expand All @@ -67,14 +68,14 @@ void __show_regs(struct pt_regs *regs, enum show_regs_mode mode)
else
savesegment(gs, gs);

show_ip(regs, KERN_DEFAULT);
show_ip(regs, log_lvl);

printk(KERN_DEFAULT "EAX: %08lx EBX: %08lx ECX: %08lx EDX: %08lx\n",
regs->ax, regs->bx, regs->cx, regs->dx);
printk(KERN_DEFAULT "ESI: %08lx EDI: %08lx EBP: %08lx ESP: %08lx\n",
regs->si, regs->di, regs->bp, regs->sp);
printk(KERN_DEFAULT "DS: %04x ES: %04x FS: %04x GS: %04x SS: %04x EFLAGS: %08lx\n",
(u16)regs->ds, (u16)regs->es, (u16)regs->fs, gs, regs->ss, regs->flags);
printk("%sEAX: %08lx EBX: %08lx ECX: %08lx EDX: %08lx\n",
log_lvl, regs->ax, regs->bx, regs->cx, regs->dx);
printk("%sESI: %08lx EDI: %08lx EBP: %08lx ESP: %08lx\n",
log_lvl, regs->si, regs->di, regs->bp, regs->sp);
printk("%sDS: %04x ES: %04x FS: %04x GS: %04x SS: %04x EFLAGS: %08lx\n",
log_lvl, (u16)regs->ds, (u16)regs->es, (u16)regs->fs, gs, regs->ss, regs->flags);

if (mode != SHOW_REGS_ALL)
return;
Expand All @@ -83,8 +84,8 @@ void __show_regs(struct pt_regs *regs, enum show_regs_mode mode)
cr2 = read_cr2();
cr3 = __read_cr3();
cr4 = __read_cr4();
printk(KERN_DEFAULT "CR0: %08lx CR2: %08lx CR3: %08lx CR4: %08lx\n",
cr0, cr2, cr3, cr4);
printk("%sCR0: %08lx CR2: %08lx CR3: %08lx CR4: %08lx\n",
log_lvl, cr0, cr2, cr3, cr4);

get_debugreg(d0, 0);
get_debugreg(d1, 1);
Expand All @@ -98,10 +99,10 @@ void __show_regs(struct pt_regs *regs, enum show_regs_mode mode)
(d6 == DR6_RESERVED) && (d7 == 0x400))
return;

printk(KERN_DEFAULT "DR0: %08lx DR1: %08lx DR2: %08lx DR3: %08lx\n",
d0, d1, d2, d3);
printk(KERN_DEFAULT "DR6: %08lx DR7: %08lx\n",
d6, d7);
printk("%sDR0: %08lx DR1: %08lx DR2: %08lx DR3: %08lx\n",
log_lvl, d0, d1, d2, d3);
printk("%sDR6: %08lx DR7: %08lx\n",
log_lvl, d6, d7);
}

void release_thread(struct task_struct *dead_task)
Expand Down
51 changes: 26 additions & 25 deletions arch/x86/kernel/process_64.c
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Original file line number Diff line number Diff line change
Expand Up @@ -62,39 +62,40 @@
#include "process.h"

/* Prints also some state that isn't saved in the pt_regs */
void __show_regs(struct pt_regs *regs, enum show_regs_mode mode)
void __show_regs(struct pt_regs *regs, enum show_regs_mode mode,
const char *log_lvl)
{
unsigned long cr0 = 0L, cr2 = 0L, cr3 = 0L, cr4 = 0L, fs, gs, shadowgs;
unsigned long d0, d1, d2, d3, d6, d7;
unsigned int fsindex, gsindex;
unsigned int ds, es;

show_iret_regs(regs, KERN_DEFAULT);
show_iret_regs(regs, log_lvl);

if (regs->orig_ax != -1)
pr_cont(" ORIG_RAX: %016lx\n", regs->orig_ax);
else
pr_cont("\n");

printk(KERN_DEFAULT "RAX: %016lx RBX: %016lx RCX: %016lx\n",
regs->ax, regs->bx, regs->cx);
printk(KERN_DEFAULT "RDX: %016lx RSI: %016lx RDI: %016lx\n",
regs->dx, regs->si, regs->di);
printk(KERN_DEFAULT "RBP: %016lx R08: %016lx R09: %016lx\n",
regs->bp, regs->r8, regs->r9);
printk(KERN_DEFAULT "R10: %016lx R11: %016lx R12: %016lx\n",
regs->r10, regs->r11, regs->r12);
printk(KERN_DEFAULT "R13: %016lx R14: %016lx R15: %016lx\n",
regs->r13, regs->r14, regs->r15);
printk("%sRAX: %016lx RBX: %016lx RCX: %016lx\n",
log_lvl, regs->ax, regs->bx, regs->cx);
printk("%sRDX: %016lx RSI: %016lx RDI: %016lx\n",
log_lvl, regs->dx, regs->si, regs->di);
printk("%sRBP: %016lx R08: %016lx R09: %016lx\n",
log_lvl, regs->bp, regs->r8, regs->r9);
printk("%sR10: %016lx R11: %016lx R12: %016lx\n",
log_lvl, regs->r10, regs->r11, regs->r12);
printk("%sR13: %016lx R14: %016lx R15: %016lx\n",
log_lvl, regs->r13, regs->r14, regs->r15);

if (mode == SHOW_REGS_SHORT)
return;

if (mode == SHOW_REGS_USER) {
rdmsrl(MSR_FS_BASE, fs);
rdmsrl(MSR_KERNEL_GS_BASE, shadowgs);
printk(KERN_DEFAULT "FS: %016lx GS: %016lx\n",
fs, shadowgs);
printk("%sFS: %016lx GS: %016lx\n",
log_lvl, fs, shadowgs);
return;
}

Expand All @@ -112,12 +113,12 @@ void __show_regs(struct pt_regs *regs, enum show_regs_mode mode)
cr3 = __read_cr3();
cr4 = __read_cr4();

printk(KERN_DEFAULT "FS: %016lx(%04x) GS:%016lx(%04x) knlGS:%016lx\n",
fs, fsindex, gs, gsindex, shadowgs);
printk(KERN_DEFAULT "CS: %04lx DS: %04x ES: %04x CR0: %016lx\n", regs->cs, ds,
es, cr0);
printk(KERN_DEFAULT "CR2: %016lx CR3: %016lx CR4: %016lx\n", cr2, cr3,
cr4);
printk("%sFS: %016lx(%04x) GS:%016lx(%04x) knlGS:%016lx\n",
log_lvl, fs, fsindex, gs, gsindex, shadowgs);
printk("%sCS: %04lx DS: %04x ES: %04x CR0: %016lx\n",
log_lvl, regs->cs, ds, es, cr0);
printk("%sCR2: %016lx CR3: %016lx CR4: %016lx\n",
log_lvl, cr2, cr3, cr4);

get_debugreg(d0, 0);
get_debugreg(d1, 1);
Expand All @@ -129,14 +130,14 @@ void __show_regs(struct pt_regs *regs, enum show_regs_mode mode)
/* Only print out debug registers if they are in their non-default state. */
if (!((d0 == 0) && (d1 == 0) && (d2 == 0) && (d3 == 0) &&
(d6 == DR6_RESERVED) && (d7 == 0x400))) {
printk(KERN_DEFAULT "DR0: %016lx DR1: %016lx DR2: %016lx\n",
d0, d1, d2);
printk(KERN_DEFAULT "DR3: %016lx DR6: %016lx DR7: %016lx\n",
d3, d6, d7);
printk("%sDR0: %016lx DR1: %016lx DR2: %016lx\n",
log_lvl, d0, d1, d2);
printk("%sDR3: %016lx DR6: %016lx DR7: %016lx\n",
log_lvl, d3, d6, d7);
}

if (boot_cpu_has(X86_FEATURE_OSPKE))
printk(KERN_DEFAULT "PKRU: %08x\n", read_pkru());
printk("%sPKRU: %08x\n", log_lvl, read_pkru());
}

void release_thread(struct task_struct *dead_task)
Expand Down

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