| Message ID | 20190430081844.22597-4-mkoutny@suse.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Reduce mmap_sem usage for args manipulation | expand |
On 30.04.2019 11:18, Michal Koutný wrote: > Since commit 88aa7cc688d4 ("mm: introduce arg_lock to protect > arg_start|end and env_start|end in mm_struct") we use arg_lock for > boundaries modifications. Synchronize prctl_set_mm with this lock and > keep mmap_sem for reading only (analogous to what we already do in > prctl_set_mm_map). > > v2: call find_vma without arg_lock held > > CC: Cyrill Gorcunov <gorcunov@gmail.com> > CC: Laurent Dufour <ldufour@linux.ibm.com> > Signed-off-by: Michal Koutný <mkoutny@suse.com> > --- > kernel/sys.c | 10 ++++++++-- > 1 file changed, 8 insertions(+), 2 deletions(-) > > diff --git a/kernel/sys.c b/kernel/sys.c > index e1acb444d7b0..641fda756575 100644 > --- a/kernel/sys.c > +++ b/kernel/sys.c > @@ -2123,9 +2123,14 @@ static int prctl_set_mm(int opt, unsigned long addr, > > error = -EINVAL; > > - down_write(&mm->mmap_sem); > + /* > + * arg_lock protects concurent updates of arg boundaries, we need mmap_sem for > + * a) concurrent sys_brk, b) finding VMA for addr validation. > + */ > + down_read(&mm->mmap_sem); > vma = find_vma(mm, addr); > > + spin_lock(&mm->arg_lock); > prctl_map.start_code = mm->start_code; > prctl_map.end_code = mm->end_code; > prctl_map.start_data = mm->start_data; > @@ -2213,7 +2218,8 @@ static int prctl_set_mm(int opt, unsigned long addr, > > error = 0; > out: > - up_write(&mm->mmap_sem); > + spin_unlock(&mm->arg_lock); > + up_read(&mm->mmap_sem); > return error; Hm, shouldn't spin_lock()/spin_unlock() pair go as a fixup to existing code in a separate patch? Without them, the existing code has a problem at least in get_mm_cmdline().
On Tue, Apr 30, 2019 at 11:55:45AM +0300, Kirill Tkhai wrote: > > - up_write(&mm->mmap_sem); > > + spin_unlock(&mm->arg_lock); > > + up_read(&mm->mmap_sem); > > return error; > > Hm, shouldn't spin_lock()/spin_unlock() pair go as a fixup to existing code > in a separate patch? > > Without them, the existing code has a problem at least in get_mm_cmdline(). Seems reasonable to merge it into patch 1.
On 30.04.2019 12:08, Cyrill Gorcunov wrote: > On Tue, Apr 30, 2019 at 11:55:45AM +0300, Kirill Tkhai wrote: >>> - up_write(&mm->mmap_sem); >>> + spin_unlock(&mm->arg_lock); >>> + up_read(&mm->mmap_sem); >>> return error; >> >> Hm, shouldn't spin_lock()/spin_unlock() pair go as a fixup to existing code >> in a separate patch? >> >> Without them, the existing code has a problem at least in get_mm_cmdline(). > > Seems reasonable to merge it into patch 1. Sounds sensibly.
diff --git a/kernel/sys.c b/kernel/sys.c index e1acb444d7b0..641fda756575 100644 --- a/kernel/sys.c +++ b/kernel/sys.c @@ -2123,9 +2123,14 @@ static int prctl_set_mm(int opt, unsigned long addr, error = -EINVAL; - down_write(&mm->mmap_sem); + /* + * arg_lock protects concurent updates of arg boundaries, we need mmap_sem for + * a) concurrent sys_brk, b) finding VMA for addr validation. + */ + down_read(&mm->mmap_sem); vma = find_vma(mm, addr); + spin_lock(&mm->arg_lock); prctl_map.start_code = mm->start_code; prctl_map.end_code = mm->end_code; prctl_map.start_data = mm->start_data; @@ -2213,7 +2218,8 @@ static int prctl_set_mm(int opt, unsigned long addr, error = 0; out: - up_write(&mm->mmap_sem); + spin_unlock(&mm->arg_lock); + up_read(&mm->mmap_sem); return error; }
Since commit 88aa7cc688d4 ("mm: introduce arg_lock to protect arg_start|end and env_start|end in mm_struct") we use arg_lock for boundaries modifications. Synchronize prctl_set_mm with this lock and keep mmap_sem for reading only (analogous to what we already do in prctl_set_mm_map). v2: call find_vma without arg_lock held CC: Cyrill Gorcunov <gorcunov@gmail.com> CC: Laurent Dufour <ldufour@linux.ibm.com> Signed-off-by: Michal Koutný <mkoutny@suse.com> --- kernel/sys.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-)