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9p: add locking to V9fsDir 

If several threads concurrently call readdir() with the same directory
stream pointer, it is possible that they all get a pointer to the same
dirent structure, whose content is overwritten each time readdir() is
called.

We must thus serialize accesses to the dirent structure.

This may be achieved with a mutex like below:

lock_mutex();

readdir();

// work with the dirent

unlock_mutex();

This patch adds all the locking, to prepare the switch to readdir().

Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
This commit is contained in:
Greg Kurz 2016-06-06 11:52:34 +02:00
parent f314ea4e30
commit 7cde47d4a8
2 changed files with 37 additions and 0 deletions
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21
hw/9pfs/9p.c
View File

@ -300,6 +300,9 @@ static V9fsFidState *alloc_fid(V9fsState *s, int32_t fid)
f->next = s->fid_list;
s->fid_list = f;
v9fs_readdir_init(&f->fs.dir);
v9fs_readdir_init(&f->fs_reclaim.dir);
return f;
}
@ -1636,6 +1639,9 @@ static int v9fs_do_readdir_with_stat(V9fsPDU *pdu,
while (1) {
v9fs_path_init(&path);
v9fs_readdir_lock(&fidp->fs.dir);
err = v9fs_co_readdir_r(pdu, fidp, dent, &result);
if (err || !result) {
break;
@ -1654,6 +1660,9 @@ static int v9fs_do_readdir_with_stat(V9fsPDU *pdu,
}
/* 11 = 7 + 4 (7 = start offset, 4 = space for storing count) */
len = pdu_marshal(pdu, 11 + count, "S", &v9stat);
v9fs_readdir_unlock(&fidp->fs.dir);
if ((len != (v9stat.size + 2)) || ((count + len) > max_count)) {
/* Ran out of buffer. Set dir back to old position and return */
v9fs_co_seekdir(pdu, fidp, saved_dir_pos);
@ -1668,6 +1677,8 @@ static int v9fs_do_readdir_with_stat(V9fsPDU *pdu,
saved_dir_pos = dent->d_off;
}
v9fs_readdir_unlock(&fidp->fs.dir);
g_free(dent);
v9fs_path_free(&path);
if (err < 0) {
@ -1815,6 +1826,8 @@ static int v9fs_do_readdir(V9fsPDU *pdu,
dent = g_malloc(sizeof(struct dirent));
while (1) {
v9fs_readdir_lock(&fidp->fs.dir);
err = v9fs_co_readdir_r(pdu, fidp, dent, &result);
if (err || !result) {
break;
@ -1822,6 +1835,8 @@ static int v9fs_do_readdir(V9fsPDU *pdu,
v9fs_string_init(&name);
v9fs_string_sprintf(&name, "%s", dent->d_name);
if ((count + v9fs_readdir_data_size(&name)) > max_count) {
v9fs_readdir_unlock(&fidp->fs.dir);
/* Ran out of buffer. Set dir back to old position and return */
v9fs_co_seekdir(pdu, fidp, saved_dir_pos);
v9fs_string_free(&name);
@ -1843,6 +1858,9 @@ static int v9fs_do_readdir(V9fsPDU *pdu,
len = pdu_marshal(pdu, 11 + count, "Qqbs",
&qid, dent->d_off,
dent->d_type, &name);
v9fs_readdir_unlock(&fidp->fs.dir);
if (len < 0) {
v9fs_co_seekdir(pdu, fidp, saved_dir_pos);
v9fs_string_free(&name);
@ -1853,6 +1871,9 @@ static int v9fs_do_readdir(V9fsPDU *pdu,
v9fs_string_free(&name);
saved_dir_pos = dent->d_off;
}
v9fs_readdir_unlock(&fidp->fs.dir);
g_free(dent);
if (err < 0) {
return err;

16
hw/9pfs/9p.h
View File

@ -169,8 +169,24 @@ typedef struct V9fsXattr
typedef struct V9fsDir {
DIR *stream;
QemuMutex readdir_mutex;
} V9fsDir;
static inline void v9fs_readdir_lock(V9fsDir *dir)
{
qemu_mutex_lock(&dir->readdir_mutex);
}
static inline void v9fs_readdir_unlock(V9fsDir *dir)
{
qemu_mutex_unlock(&dir->readdir_mutex);
}
static inline void v9fs_readdir_init(V9fsDir *dir)
{
qemu_mutex_init(&dir->readdir_mutex);
}
/*
* Filled by fs driver on open and other
* calls.