| Message ID | 20190502125203.24014-3-mkoutny@suse.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Reduce mmap_sem usage for args manipulation | expand |
On Thu, May 02, 2019 at 02:52:03PM +0200, Michal Koutný wrote: > The commit a3b609ef9f8b ("proc read mm's {arg,env}_{start,end} with mmap > semaphore taken.") added synchronization of reading argument/environment > boundaries under mmap_sem. Later commit 88aa7cc688d4 ("mm: introduce > arg_lock to protect arg_start|end and env_start|end in mm_struct") > avoided the coarse use of mmap_sem in similar situations. But there > still remained two places that (mis)use mmap_sem. > > get_cmdline should also use arg_lock instead of mmap_sem when it reads the > boundaries. > > The second place that should use arg_lock is in prctl_set_mm. By > protecting the boundaries fields with the arg_lock, we can downgrade > mmap_sem to reader lock (analogous to what we already do in > prctl_set_mm_map). > > v2: call find_vma without arg_lock held > v3: squashed get_cmdline arg_lock patch > > Fixes: 88aa7cc688d4 ("mm: introduce arg_lock to protect arg_start|end and env_start|end in mm_struct") > Cc: Yang Shi <yang.shi@linux.alibaba.com> > Cc: Mateusz Guzik <mguzik@redhat.com> > CC: Cyrill Gorcunov <gorcunov@gmail.com> > Co-developed-by: Laurent Dufour <ldufour@linux.ibm.com> > Signed-off-by: Laurent Dufour <ldufour@linux.ibm.com> > Signed-off-by: Michal Koutný <mkoutny@suse.com> Reviewed-by: Cyrill Gorcunov <gorcunov@gmail.com>
On 02.05.2019 15:52, Michal Koutný wrote: > The commit a3b609ef9f8b ("proc read mm's {arg,env}_{start,end} with mmap > semaphore taken.") added synchronization of reading argument/environment > boundaries under mmap_sem. Later commit 88aa7cc688d4 ("mm: introduce > arg_lock to protect arg_start|end and env_start|end in mm_struct") > avoided the coarse use of mmap_sem in similar situations. But there > still remained two places that (mis)use mmap_sem. > > get_cmdline should also use arg_lock instead of mmap_sem when it reads the > boundaries. > > The second place that should use arg_lock is in prctl_set_mm. By > protecting the boundaries fields with the arg_lock, we can downgrade > mmap_sem to reader lock (analogous to what we already do in > prctl_set_mm_map). > > v2: call find_vma without arg_lock held > v3: squashed get_cmdline arg_lock patch > > Fixes: 88aa7cc688d4 ("mm: introduce arg_lock to protect arg_start|end and env_start|end in mm_struct") > Cc: Yang Shi <yang.shi@linux.alibaba.com> > Cc: Mateusz Guzik <mguzik@redhat.com> > CC: Cyrill Gorcunov <gorcunov@gmail.com> > Co-developed-by: Laurent Dufour <ldufour@linux.ibm.com> > Signed-off-by: Laurent Dufour <ldufour@linux.ibm.com> > Signed-off-by: Michal Koutný <mkoutny@suse.com> Reviewed-by: Kirill Tkhai <ktkhai@virtuozzo.com> > --- > kernel/sys.c | 10 ++++++++-- > mm/util.c | 4 ++-- > 2 files changed, 10 insertions(+), 4 deletions(-) > > diff --git a/kernel/sys.c b/kernel/sys.c > index 5e0a5edf47f8..14be57840511 100644 > --- a/kernel/sys.c > +++ b/kernel/sys.c > @@ -2122,9 +2122,14 @@ 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; > @@ -2212,7 +2217,8 @@ 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; > } > > diff --git a/mm/util.c b/mm/util.c > index 43a2984bccaa..5cf0e84a0823 100644 > --- a/mm/util.c > +++ b/mm/util.c > @@ -758,12 +758,12 @@ int get_cmdline(struct task_struct *task, char *buffer, int buflen) > if (!mm->arg_end) > goto out_mm; /* Shh! No looking before we're done */ > > - down_read(&mm->mmap_sem); > + spin_lock(&mm->arg_lock); > arg_start = mm->arg_start; > arg_end = mm->arg_end; > env_start = mm->env_start; > env_end = mm->env_end; > - up_read(&mm->mmap_sem); > + spin_unlock(&mm->arg_lock); > > len = arg_end - arg_start; > >
On Thu 02-05-19 14:52:03, Michal Koutny wrote: > The commit a3b609ef9f8b ("proc read mm's {arg,env}_{start,end} with mmap > semaphore taken.") added synchronization of reading argument/environment > boundaries under mmap_sem. Later commit 88aa7cc688d4 ("mm: introduce > arg_lock to protect arg_start|end and env_start|end in mm_struct") > avoided the coarse use of mmap_sem in similar situations. But there > still remained two places that (mis)use mmap_sem. > > get_cmdline should also use arg_lock instead of mmap_sem when it reads the > boundaries. > > The second place that should use arg_lock is in prctl_set_mm. By > protecting the boundaries fields with the arg_lock, we can downgrade > mmap_sem to reader lock (analogous to what we already do in > prctl_set_mm_map). > > v2: call find_vma without arg_lock held > v3: squashed get_cmdline arg_lock patch > > Fixes: 88aa7cc688d4 ("mm: introduce arg_lock to protect arg_start|end and env_start|end in mm_struct") > Cc: Yang Shi <yang.shi@linux.alibaba.com> > Cc: Mateusz Guzik <mguzik@redhat.com> > CC: Cyrill Gorcunov <gorcunov@gmail.com> > Co-developed-by: Laurent Dufour <ldufour@linux.ibm.com> > Signed-off-by: Laurent Dufour <ldufour@linux.ibm.com> > Signed-off-by: Michal Koutný <mkoutny@suse.com> Just a nit. S-o-b chain is not correct here. The first s-o-b should match the author (From) of the patch. Acked-by: Michal Hocko <mhocko@suse.com> > --- > kernel/sys.c | 10 ++++++++-- > mm/util.c | 4 ++-- > 2 files changed, 10 insertions(+), 4 deletions(-) > > diff --git a/kernel/sys.c b/kernel/sys.c > index 5e0a5edf47f8..14be57840511 100644 > --- a/kernel/sys.c > +++ b/kernel/sys.c > @@ -2122,9 +2122,14 @@ 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; > @@ -2212,7 +2217,8 @@ 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; > } > > diff --git a/mm/util.c b/mm/util.c > index 43a2984bccaa..5cf0e84a0823 100644 > --- a/mm/util.c > +++ b/mm/util.c > @@ -758,12 +758,12 @@ int get_cmdline(struct task_struct *task, char *buffer, int buflen) > if (!mm->arg_end) > goto out_mm; /* Shh! No looking before we're done */ > > - down_read(&mm->mmap_sem); > + spin_lock(&mm->arg_lock); > arg_start = mm->arg_start; > arg_end = mm->arg_end; > env_start = mm->env_start; > env_end = mm->env_end; > - up_read(&mm->mmap_sem); > + spin_unlock(&mm->arg_lock); > > len = arg_end - arg_start; > > -- > 2.16.4
diff --git a/kernel/sys.c b/kernel/sys.c index 5e0a5edf47f8..14be57840511 100644 --- a/kernel/sys.c +++ b/kernel/sys.c @@ -2122,9 +2122,14 @@ 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; @@ -2212,7 +2217,8 @@ 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; } diff --git a/mm/util.c b/mm/util.c index 43a2984bccaa..5cf0e84a0823 100644 --- a/mm/util.c +++ b/mm/util.c @@ -758,12 +758,12 @@ int get_cmdline(struct task_struct *task, char *buffer, int buflen) if (!mm->arg_end) goto out_mm; /* Shh! No looking before we're done */ - down_read(&mm->mmap_sem); + spin_lock(&mm->arg_lock); arg_start = mm->arg_start; arg_end = mm->arg_end; env_start = mm->env_start; env_end = mm->env_end; - up_read(&mm->mmap_sem); + spin_unlock(&mm->arg_lock); len = arg_end - arg_start;
The commit a3b609ef9f8b ("proc read mm's {arg,env}_{start,end} with mmap semaphore taken.") added synchronization of reading argument/environment boundaries under mmap_sem. Later commit 88aa7cc688d4 ("mm: introduce arg_lock to protect arg_start|end and env_start|end in mm_struct") avoided the coarse use of mmap_sem in similar situations. But there still remained two places that (mis)use mmap_sem. get_cmdline should also use arg_lock instead of mmap_sem when it reads the boundaries. The second place that should use arg_lock is in prctl_set_mm. By protecting the boundaries fields with the arg_lock, we can downgrade mmap_sem to reader lock (analogous to what we already do in prctl_set_mm_map). v2: call find_vma without arg_lock held v3: squashed get_cmdline arg_lock patch Fixes: 88aa7cc688d4 ("mm: introduce arg_lock to protect arg_start|end and env_start|end in mm_struct") Cc: Yang Shi <yang.shi@linux.alibaba.com> Cc: Mateusz Guzik <mguzik@redhat.com> CC: Cyrill Gorcunov <gorcunov@gmail.com> Co-developed-by: Laurent Dufour <ldufour@linux.ibm.com> Signed-off-by: Laurent Dufour <ldufour@linux.ibm.com> Signed-off-by: Michal Koutný <mkoutny@suse.com> --- kernel/sys.c | 10 ++++++++-- mm/util.c | 4 ++-- 2 files changed, 10 insertions(+), 4 deletions(-)