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filemap: Get vma mnt_id early

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We have a, well, issue with how we calculate the vma's mnt_id.

Right now get one via criu side file descriptor that it got by
opening the /proc/pid/map_files/ link. The problem is that these
descriptors are 'merged' or 'borrowed' by adjacent vmas from
previous ones. Thus, getting the mnt_id value for each of them
makes no sense -- these files are the same.

So move this mnt_id getting earlier into vma parsing code. This
brings a potential problem -- if we have two adjacent vmas
mapping the same inode (dev:ino pair) but living in different
mount namespaces -- this check would produce wrong result.
"Wrong" from the perspective that on restore correct file would
be opened from wrong namespace.

I propose to live with it, since this is not worse than the
--evasive-devices option, it's _very_ unlikely, but saves a lot
of openeings.

Note, that in case app switched mount namespace and then mapped
some new library (with dlopen) things would work correctly -- new
vmas will likely be not adjacent and for different dev:ino.

Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
This commit is contained in:
Pavel Emelyanov 2014-09-23 20:32:00 +04:00
parent f84d19e09a
commit e651a6eba4
4 changed files with 26 additions and 14 deletions
Download patch file Download diff file Expand all files Collapse all files

15
cr-dump.c
View file

@ -247,17 +247,6 @@ static int collect_fds(pid_t pid, struct parasite_drain_fd *dfds)
return 0;
}
static int get_fd_mntid(int fd, int *mnt_id)
{
struct fdinfo_common fdinfo = { .mnt_id = -1};
if (parse_fdinfo(fd, FD_TYPES__UND, NULL, &fdinfo))
return -1;
*mnt_id = fdinfo.mnt_id;
return 0;
}
static int fill_fd_params_special(int fd, struct fd_parms *p)
{
*p = FD_PARMS_INIT;
@ -371,6 +360,7 @@ static int dump_filemap(pid_t pid, struct vma_area *vma_area,
BUG_ON(!vma_area->vmst);
p.stat = *vma_area->vmst;
p.mnt_id = vma_area->mnt_id;
/*
* AUFS support to compensate for the kernel bug
@ -388,9 +378,6 @@ static int dump_filemap(pid_t pid, struct vma_area *vma_area,
p.link = &aufs_link;
}
if (get_fd_mntid(vma_area->vm_file_fd, &p.mnt_id))
return -1;
/* Flags will be set during restore in get_filemap_fd() */
if (fd_id_generate_special(&p, &id))

1
include/proc_parse.h
View file

@ -212,6 +212,7 @@ extern int parse_fdinfo_pid(int pid, int fd, int type,
int (*cb)(union fdinfo_entries *e, void *arg), void *arg);
extern int parse_cpuinfo_features(int (*handler)(char *tok));
extern int parse_file_locks(void);
extern int get_fd_mntid(int fd, int *mnt_id);
struct pid;
extern int parse_threads(int pid, struct pid **_t, int *_n);

1
include/vma.h
View file

@ -50,6 +50,7 @@ struct vma_area {
*/
bool file_borrowed;
struct stat *vmst;
int mnt_id;
};
struct /* for restore */ {

23
proc_parse.c
View file

@ -214,6 +214,14 @@ static int vma_get_mapfile(struct vma_area *vma, DIR *mfd,
vma->vm_file_fd = prev->vm_file_fd;
if (prev->e->status & VMA_AREA_SOCKET)
vma->e->status |= VMA_AREA_SOCKET | VMA_AREA_REGULAR;
/*
* FIXME -- in theory there can be vmas that have
* dev:ino match, but live in different mount
* namespaces. However, we only borrow files for
* subsequent vmas. These are _very_ likely to
* have files from the same namespaces.
*/
vma->file_borrowed = true;
return 0;
@ -454,6 +462,7 @@ int parse_smaps(pid_t pid, struct vm_area_list *vma_area_list, bool use_map_file
vma_area->e->status = prev->e->status;
vma_area->e->shmid = prev->e->shmid;
vma_area->vmst = prev->vmst;
vma_area->mnt_id = prev->mnt_id;
} else if (vma_area->vm_file_fd >= 0) {
struct stat *st_buf;
@ -505,6 +514,9 @@ int parse_smaps(pid_t pid, struct vm_area_list *vma_area_list, bool use_map_file
else
vma_area->e->status |= VMA_FILE_SHARED;
}
if (get_fd_mntid(vma_area->vm_file_fd, &vma_area->mnt_id))
return -1;
} else {
/*
* No file but mapping -- anonymous one.
@ -1423,6 +1435,17 @@ int parse_fdinfo(int fd, int type,
return parse_fdinfo_pid_s(PROC_SELF, fd, type, cb, arg);
}
int get_fd_mntid(int fd, int *mnt_id)
{
struct fdinfo_common fdinfo = { .mnt_id = -1};
if (parse_fdinfo(fd, FD_TYPES__UND, NULL, &fdinfo))
return -1;
*mnt_id = fdinfo.mnt_id;
return 0;
}
static int parse_file_lock_buf(char *buf, struct file_lock *fl,
bool is_blocked)
{