Message ID | 510B22C2.90606@windriver.com (mailing list archive) |
---|---|
State | Rejected |
Headers | show |
On Thu, 2013-01-31 at 20:04 -0600, Jason Wessel wrote: > > diff --git a/arch/powerpc/kernel/kgdb.c b/arch/powerpc/kernel/kgdb.c > > index 8747447..5ca82cd 100644 > > --- a/arch/powerpc/kernel/kgdb.c > > +++ b/arch/powerpc/kernel/kgdb.c > > @@ -154,12 +154,12 @@ static int kgdb_handle_breakpoint(struct pt_regs *regs) > > static int kgdb_singlestep(struct pt_regs *regs) > > { > > struct thread_info *thread_info, *exception_thread_info; > > - struct thread_info *backup_current_thread_info = \ > > - (struct thread_info *)kmalloc(sizeof(struct thread_info), GFP_KERNEL); > > + struct thread_info *backup_current_thread_info; > > > > Woh... This is definitely wrong. You have found a problem for sure, > but this is not the right way to fix it. > > It is not a good idea to kmalloc while single stepping because you can > hang the kernel if you single step any operation in kmalloc(). Ok. I applied the fix because it was obviously correct vs. the previous version of the code (ie. the kmalloc was already there) > I am in the process of going through all the kgdb mails from the last > few months while I had been away from the project, so I didn't catch > this one and I see it has upstream commit (fefd9e6f8). I'll submit > another patch to fix this the right way and use a static variable. > This is ok to use a static variable here because this is not something > we can recursively call at a single CPU level. But a static will be shared by all CPUs or do you mean a per-cpu one ? > If Ben prefers we not burn the memory unless kgdb is active we can > kmalloc / kfree the space we need at the time that kgdb is > initialized. Else we can go with this patch you see below. We'll see > what Ben desires. What about the stack ? thread info isn't very big... Cheers, Ben. > ----- > diff --git a/arch/powerpc/kernel/kgdb.c b/arch/powerpc/kernel/kgdb.c > index a7bc752..bb12c8b 100644 > --- a/arch/powerpc/kernel/kgdb.c > +++ b/arch/powerpc/kernel/kgdb.c > @@ -151,15 +151,16 @@ static int kgdb_handle_breakpoint(struct pt_regs *regs) > return 1; > } > > +static struct thread_info kgdb_backup_thread_info[NR_CPUS]; > + > static int kgdb_singlestep(struct pt_regs *regs) > { > struct thread_info *thread_info, *exception_thread_info; > - struct thread_info *backup_current_thread_info; > + int cpu = raw_smp_processor_id(); > > if (user_mode(regs)) > return 0; > > - backup_current_thread_info = (struct thread_info *)kmalloc(sizeof(struct thread_info), GFP_KERNEL); > /* > * On Book E and perhaps other processors, singlestep is handled on > * the critical exception stack. This causes current_thread_info() > @@ -175,7 +176,7 @@ static int kgdb_singlestep(struct pt_regs *regs) > > if (thread_info != exception_thread_info) { > /* Save the original current_thread_info. */ > - memcpy(backup_current_thread_info, exception_thread_info, sizeof *thread_info); > + memcpy(&kgdb_backup_thread_info[cpu], exception_thread_info, sizeof *thread_info); > memcpy(exception_thread_info, thread_info, sizeof *thread_info); > } > > @@ -183,9 +184,8 @@ static int kgdb_singlestep(struct pt_regs *regs) > > if (thread_info != exception_thread_info) > /* Restore current_thread_info lastly. */ > - memcpy(exception_thread_info, backup_current_thread_info, sizeof *thread_info); > + memcpy(exception_thread_info, &kgdb_backup_thread_info[cpu], sizeof *thread_info); > > - kfree(backup_current_thread_info); > return 1; > } > > > ----- > > > Thanks, > Jason. > > > > > > if (user_mode(regs)) > > return 0; > > > > + backup_current_thread_info = (struct thread_info *)kmalloc(sizeof(struct thread_info), GFP_KERNEL); > > /* > > * On Book E and perhaps other processors, singlestep is handled on > > * the critical exception stack. This causes current_thread_info() > > @@ -185,6 +185,7 @@ static int kgdb_singlestep(struct pt_regs *regs) > > /* Restore current_thread_info lastly. */ > > memcpy(exception_thread_info, backup_current_thread_info, sizeof *thread_info); > > > > + kfree(backup_current_thread_info); > > return 1; > > } > > > >
On 02/08/2013 10:41 AM, Benjamin Herrenschmidt wrote: > On Thu, 2013-01-31 at 20:04 -0600, Jason Wessel wrote: > >>> diff --git a/arch/powerpc/kernel/kgdb.c b/arch/powerpc/kernel/kgdb.c >>> index 8747447..5ca82cd 100644 >>> --- a/arch/powerpc/kernel/kgdb.c >>> +++ b/arch/powerpc/kernel/kgdb.c >>> @@ -154,12 +154,12 @@ static int kgdb_handle_breakpoint(struct pt_regs *regs) >>> static int kgdb_singlestep(struct pt_regs *regs) >>> { >>> struct thread_info *thread_info, *exception_thread_info; >>> - struct thread_info *backup_current_thread_info = \ >>> - (struct thread_info *)kmalloc(sizeof(struct thread_info), GFP_KERNEL); >>> + struct thread_info *backup_current_thread_info; >> >> >> >> Woh... This is definitely wrong. You have found a problem for sure, >> but this is not the right way to fix it. >> >> It is not a good idea to kmalloc while single stepping because you can >> hang the kernel if you single step any operation in kmalloc(). > > Ok. I applied the fix because it was obviously correct vs. the previous > version of the code (ie. the kmalloc was already there) > >> I am in the process of going through all the kgdb mails from the last >> few months while I had been away from the project, so I didn't catch >> this one and I see it has upstream commit (fefd9e6f8). I'll submit >> another patch to fix this the right way and use a static variable. >> This is ok to use a static variable here because this is not something >> we can recursively call at a single CPU level. > > But a static will be shared by all CPUs or do you mean a per-cpu one ? > >> If Ben prefers we not burn the memory unless kgdb is active we can >> kmalloc / kfree the space we need at the time that kgdb is >> initialized. Else we can go with this patch you see below. We'll see >> what Ben desires. > > What about the stack ? thread info isn't very big... Actually booke already copy the thread_info when we enter the debug exception, and I will send a patch to do the same thing for book3e, so I also remove these copying action here then we're happy without these nasty stuff :) Tiejun > > Cheers, > Ben. > >> ----- >> diff --git a/arch/powerpc/kernel/kgdb.c b/arch/powerpc/kernel/kgdb.c >> index a7bc752..bb12c8b 100644 >> --- a/arch/powerpc/kernel/kgdb.c >> +++ b/arch/powerpc/kernel/kgdb.c >> @@ -151,15 +151,16 @@ static int kgdb_handle_breakpoint(struct pt_regs *regs) >> return 1; >> } >> >> +static struct thread_info kgdb_backup_thread_info[NR_CPUS]; >> + >> static int kgdb_singlestep(struct pt_regs *regs) >> { >> struct thread_info *thread_info, *exception_thread_info; >> - struct thread_info *backup_current_thread_info; >> + int cpu = raw_smp_processor_id(); >> >> if (user_mode(regs)) >> return 0; >> >> - backup_current_thread_info = (struct thread_info *)kmalloc(sizeof(struct thread_info), GFP_KERNEL); >> /* >> * On Book E and perhaps other processors, singlestep is handled on >> * the critical exception stack. This causes current_thread_info() >> @@ -175,7 +176,7 @@ static int kgdb_singlestep(struct pt_regs *regs) >> >> if (thread_info != exception_thread_info) { >> /* Save the original current_thread_info. */ >> - memcpy(backup_current_thread_info, exception_thread_info, sizeof *thread_info); >> + memcpy(&kgdb_backup_thread_info[cpu], exception_thread_info, sizeof *thread_info); >> memcpy(exception_thread_info, thread_info, sizeof *thread_info); >> } >> >> @@ -183,9 +184,8 @@ static int kgdb_singlestep(struct pt_regs *regs) >> >> if (thread_info != exception_thread_info) >> /* Restore current_thread_info lastly. */ >> - memcpy(exception_thread_info, backup_current_thread_info, sizeof *thread_info); >> + memcpy(exception_thread_info, &kgdb_backup_thread_info[cpu], sizeof *thread_info); >> >> - kfree(backup_current_thread_info); >> return 1; >> } >> >> >> ----- >> >> >> Thanks, >> Jason. >> >> >>> >>> if (user_mode(regs)) >>> return 0; >>> >>> + backup_current_thread_info = (struct thread_info *)kmalloc(sizeof(struct thread_info), GFP_KERNEL); >>> /* >>> * On Book E and perhaps other processors, singlestep is handled on >>> * the critical exception stack. This causes current_thread_info() >>> @@ -185,6 +185,7 @@ static int kgdb_singlestep(struct pt_regs *regs) >>> /* Restore current_thread_info lastly. */ >>> memcpy(exception_thread_info, backup_current_thread_info, sizeof *thread_info); >>> >>> + kfree(backup_current_thread_info); >>> return 1; >>> } >>> >>> > > > >
diff --git a/arch/powerpc/kernel/kgdb.c b/arch/powerpc/kernel/kgdb.c index a7bc752..bb12c8b 100644 --- a/arch/powerpc/kernel/kgdb.c +++ b/arch/powerpc/kernel/kgdb.c @@ -151,15 +151,16 @@ static int kgdb_handle_breakpoint(struct pt_regs *regs) return 1; } +static struct thread_info kgdb_backup_thread_info[NR_CPUS]; + static int kgdb_singlestep(struct pt_regs *regs) { struct thread_info *thread_info, *exception_thread_info; - struct thread_info *backup_current_thread_info; + int cpu = raw_smp_processor_id(); if (user_mode(regs)) return 0; - backup_current_thread_info = (struct thread_info *)kmalloc(sizeof(struct thread_info), GFP_KERNEL); /* * On Book E and perhaps other processors, singlestep is handled on * the critical exception stack. This causes current_thread_info() @@ -175,7 +176,7 @@ static int kgdb_singlestep(struct pt_regs *regs) if (thread_info != exception_thread_info) { /* Save the original current_thread_info. */ - memcpy(backup_current_thread_info, exception_thread_info, sizeof *thread_info); + memcpy(&kgdb_backup_thread_info[cpu], exception_thread_info, sizeof *thread_info); memcpy(exception_thread_info, thread_info, sizeof *thread_info); } @@ -183,9 +184,8 @@ static int kgdb_singlestep(struct pt_regs *regs) if (thread_info != exception_thread_info) /* Restore current_thread_info lastly. */ - memcpy(exception_thread_info, backup_current_thread_info, sizeof *thread_info); + memcpy(exception_thread_info, &kgdb_backup_thread_info[cpu], sizeof *thread_info); - kfree(backup_current_thread_info); return 1; }