| Message ID | 20230710212958.274126-1-zhengyejian1@huawei.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | ftrace: Fix possible warning on checking all pages used in ftrace_process_locs() | expand |
On Tue, 11 Jul 2023 05:29:58 +0800 Zheng Yejian <zhengyejian1@huawei.com> wrote: > As comments in ftrace_process_locs(), there may be NULL pointers in > mcount_loc section: > > Some architecture linkers will pad between > > the different mcount_loc sections of different > > object files to satisfy alignments. > > Skip any NULL pointers. > > After 20e5227e9f55 ("ftrace: allow NULL pointers in mcount_loc"), > NULL pointers will be accounted when allocating ftrace pages but > skipped before adding into ftrace pages, this may result in some > pages not being used. Then after 706c81f87f84 ("ftrace: Remove extra > helper functions"), warning may occur at: > WARN_ON(pg->next); > > So we may need to skip NULL pointers before allocating ftrace pages. > > Fixes: 706c81f87f84 ("ftrace: Remove extra helper functions") > Signed-off-by: Zheng Yejian <zhengyejian1@huawei.com> > --- > kernel/trace/ftrace.c | 10 ++++++++++ > 1 file changed, 10 insertions(+) > > diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c > index 3740aca79fe7..5b474165df31 100644 > --- a/kernel/trace/ftrace.c > +++ b/kernel/trace/ftrace.c > @@ -6485,6 +6485,16 @@ static int ftrace_process_locs(struct module *mod, > if (!count) > return 0; > > + p = start; > + while (p < end) { > + /* > + * Refer to conments below, there may be NULL pointers, > + * skip them before allocating pages > + */ > + addr = ftrace_call_adjust(*p++); > + if (!addr) > + count--; > + } My main concern about this is the added overhead during boot to process this. There's 10s of thousands of functions, so this loop will be 10s of thousands. I also don't like that this is an unconditional loop (meaning it executes even when it is unnecessary to do so). > /* > * Sorting mcount in vmlinux at build time depend on > * CONFIG_BUILDTIME_MCOUNT_SORT, while mcount loc in How about something like this? -- Steve diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c index b24c573934af..acd033371721 100644 --- a/kernel/trace/ftrace.c +++ b/kernel/trace/ftrace.c @@ -6474,6 +6474,7 @@ static int ftrace_process_locs(struct module *mod, struct ftrace_page *start_pg; struct ftrace_page *pg; struct dyn_ftrace *rec; + unsigned long skipped = 0; unsigned long count; unsigned long *p; unsigned long addr; @@ -6536,8 +6537,10 @@ static int ftrace_process_locs(struct module *mod, * object files to satisfy alignments. * Skip any NULL pointers. */ - if (!addr) + if (!addr) { + skipped++; continue; + } end_offset = (pg->index+1) * sizeof(pg->records[0]); if (end_offset > PAGE_SIZE << pg->order) { @@ -6551,12 +6554,24 @@ static int ftrace_process_locs(struct module *mod, rec->ip = addr; } - /* We should have used all pages */ - WARN_ON(pg->next); - /* Assign the last page to ftrace_pages */ ftrace_pages = pg; + /* We should have used all pages unless we skipped some */ + if (pg->next) { + WARN_ON(!skipped); + while (ftrace_pages->next) { + pg = ftrace_pages->next; + ftrace_pages->next = pg->next; + if (pg->records) { + free_pages((unsigned long)pg->records, pg->order); + ftrace_number_of_pages -= 1 << pg->order; + } + kfree(pg); + ftrace_number_of_groups--; + } + } + /* * We only need to disable interrupts on start up * because we are modifying code that an interrupt
On 2023/7/10 22:46, Steven Rostedt wrote: > On Tue, 11 Jul 2023 05:29:58 +0800 > Zheng Yejian <zhengyejian1@huawei.com> wrote: > >> As comments in ftrace_process_locs(), there may be NULL pointers in >> mcount_loc section: >> > Some architecture linkers will pad between >> > the different mcount_loc sections of different >> > object files to satisfy alignments. >> > Skip any NULL pointers. >> >> After 20e5227e9f55 ("ftrace: allow NULL pointers in mcount_loc"), >> NULL pointers will be accounted when allocating ftrace pages but >> skipped before adding into ftrace pages, this may result in some >> pages not being used. Then after 706c81f87f84 ("ftrace: Remove extra >> helper functions"), warning may occur at: >> WARN_ON(pg->next); >> >> So we may need to skip NULL pointers before allocating ftrace pages. >> >> Fixes: 706c81f87f84 ("ftrace: Remove extra helper functions") >> Signed-off-by: Zheng Yejian <zhengyejian1@huawei.com> >> --- >> kernel/trace/ftrace.c | 10 ++++++++++ >> 1 file changed, 10 insertions(+) >> >> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c >> index 3740aca79fe7..5b474165df31 100644 >> --- a/kernel/trace/ftrace.c >> +++ b/kernel/trace/ftrace.c >> @@ -6485,6 +6485,16 @@ static int ftrace_process_locs(struct module *mod, >> if (!count) >> return 0; >> >> + p = start; >> + while (p < end) { >> + /* >> + * Refer to conments below, there may be NULL pointers, >> + * skip them before allocating pages >> + */ >> + addr = ftrace_call_adjust(*p++); >> + if (!addr) >> + count--; >> + } > > My main concern about this is the added overhead during boot to process > this. There's 10s of thousands of functions, so this loop will be 10s of > thousands. I also don't like that this is an unconditional loop (meaning it > executes even when it is unnecessary to do so). > Agreed! The added overhead probably superfluousin in most cases. > >> /* >> * Sorting mcount in vmlinux at build time depend on >> * CONFIG_BUILDTIME_MCOUNT_SORT, while mcount loc in > > How about something like this? > > -- Steve > > diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c > index b24c573934af..acd033371721 100644 > --- a/kernel/trace/ftrace.c > +++ b/kernel/trace/ftrace.c > @@ -6474,6 +6474,7 @@ static int ftrace_process_locs(struct module *mod, > struct ftrace_page *start_pg; > struct ftrace_page *pg; > struct dyn_ftrace *rec; > + unsigned long skipped = 0; > unsigned long count; > unsigned long *p; > unsigned long addr; > @@ -6536,8 +6537,10 @@ static int ftrace_process_locs(struct module *mod, > * object files to satisfy alignments. > * Skip any NULL pointers. > */ > - if (!addr) > + if (!addr) { > + skipped++; > continue; > + } > > end_offset = (pg->index+1) * sizeof(pg->records[0]); > if (end_offset > PAGE_SIZE << pg->order) { > @@ -6551,12 +6554,24 @@ static int ftrace_process_locs(struct module *mod, > rec->ip = addr; > } > > - /* We should have used all pages */ > - WARN_ON(pg->next); > - > /* Assign the last page to ftrace_pages */ > ftrace_pages = pg; > > + /* We should have used all pages unless we skipped some */ > + if (pg->next) { > + WARN_ON(!skipped); > + while (ftrace_pages->next) { > + pg = ftrace_pages->next; > + ftrace_pages->next = pg->next; > + if (pg->records) { > + free_pages((unsigned long)pg->records, pg->order); > + ftrace_number_of_pages -= 1 << pg->order; > + } > + kfree(pg); > + ftrace_number_of_groups--; > + } Do we only need to free the pages that not being used? > + } > + > /* > * We only need to disable interrupts on start up > * because we are modifying code that an interrupt >
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c index 3740aca79fe7..5b474165df31 100644 --- a/kernel/trace/ftrace.c +++ b/kernel/trace/ftrace.c @@ -6485,6 +6485,16 @@ static int ftrace_process_locs(struct module *mod, if (!count) return 0; + p = start; + while (p < end) { + /* + * Refer to conments below, there may be NULL pointers, + * skip them before allocating pages + */ + addr = ftrace_call_adjust(*p++); + if (!addr) + count--; + } /* * Sorting mcount in vmlinux at build time depend on * CONFIG_BUILDTIME_MCOUNT_SORT, while mcount loc in