[PATCH 11/19] FS: set PF_FSTRANS while holding mmap_sem in exec.c

NeilBrown
2014-04-16T04:19:08Z

Because mmap_sem is sometimes(*) taken while holding a sock lock,
and the sock lock might be needed for reclaim (at least when loop-back
NFS is active), we must not block on FS reclaim while mmap_sem is
held.

exec.c allocates memory while holding mmap_sem, and so needs
PF_FSTRANS protection.

* lockdep reports:
[ 57.653355] [<ffffffff810eb068>] lock_acquire+0xa8/0x1f0
[ 57.653355] [<ffffffff811835a4>] might_fault+0x84/0xb0
[ 57.653355] [<ffffffff81aec65d>] do_ip_setsockopt.isra.18+0x93d/0xed0
[ 57.653355] [<ffffffff81aecc17>] ip_setsockopt+0x27/0x90
[ 57.653355] [<ffffffff81b15146>] udp_setsockopt+0x16/0x30
[ 57.653355] [<ffffffff81a913cf>] sock_common_setsockopt+0xf/0x20
[ 57.653355] [<ffffffff81a9075e>] SyS_setsockopt+0x5e/0xc0
[ 57.653355] [<ffffffff81c3d062>] system_call_fastpath+0x16/0x1b

to explain why mmap_sem might be taken while sock lock is held.

Signed-off-by: NeilBrown <neilb@suse.de>
---
fs/exec.c | 6 ++++++
1 file changed, 6 insertions(+)

diff --git a/fs/exec.c b/fs/exec.c
index 3d78fccdd723..2c70a03ddb2b 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -652,6 +652,7 @@ int setup_arg_pages(struct linux_binprm *bprm,
unsigned long stack_size;
unsigned long stack_expand;
unsigned long rlim_stack;
+ unsigned int pflags;

#ifdef CONFIG_STACK_GROWSUP
/* Limit stack size to 1GB */
@@ -688,6 +689,7 @@ int setup_arg_pages(struct linux_binprm *bprm,

down_write(&mm->mmap_sem);
vm_flags = VM_STACK_FLAGS;
+ current_set_flags_nested(&pflags, PF_FSTRANS);

/*
* Adjust stack execute permissions; explicitly enable for
@@ -741,6 +743,7 @@ int setup_arg_pages(struct linux_binprm *bprm,
ret = -EFAULT;

out_unlock:
+ current_restore_flags_nested(&pflags, PF_FSTRANS);
up_write(&mm->mmap_sem);
return ret;
}
@@ -1369,6 +1372,7 @@ int search_binary_handler(struct linux_binprm *bprm)
bool need_retry = IS_ENABLED(CONFIG_MODULES);
struct linux_binfmt *fmt;
int retval;
+ unsigned int pflags;

/* This allows 4 levels of binfmt rewrites before failing hard. */
if (bprm->recursion_depth > 5)
@@ -1381,6 +1385,7 @@ int search_binary_handler(struct linux_binprm *bprm)
retval = -ENOENT;
retry:
read_lock(&binfmt_lock);
+ current_set_flags_nested(&pflags, PF_FSTRANS);
list_for_each_entry(fmt, &formats, lh) {
if (!try_module_get(fmt->module))
continue;
@@ -1396,6 +1401,7 @@ int search_binary_handler(struct linux_binprm *bprm)
read_lock(&binfmt_lock);
put_binfmt(fmt);
}
+ current_restore_flags_nested(&pflags, PF_FSTRANS);
read_unlock(&binfmt_lock);

if (need_retry && retval == -ENOEXEC) {