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Fix race conditions in emlog #17

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Fix race conditions in emlog #17

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fe0ea57
Fix race conditions in emlog
vishwamartur Dec 15, 2024
756cb4c
Update emlog.c
vishwamartur Dec 16, 2024
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17 changes: 14 additions & 3 deletions emlog.c
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Original file line number Diff line number Diff line change
@@ -1,4 +1,3 @@

/*
* EMLOG: the EMbedded-device LOGger
*
Expand Down Expand Up @@ -90,7 +89,9 @@ static dev_t emlog_dev_type = 0;
static struct cdev *emlog_cdev = NULL;
static struct class *emlog_class = NULL;
static struct device *emlog_dev_reg;
static struct emlog_info *emlog_info_list = NULL;

static struct emlog_info *emlog_info_list = NULL; // protected by emlog_info_list_lock
static spinlock_t emlog_info_list_lock;

module_param(emlog_autofree, bool, 0644);
module_param(emlog_debug, bool, 0644);
Expand All @@ -109,9 +110,13 @@ static struct emlog_info *get_einfo(const struct inode *inode)
if (inode == NULL)
return NULL;

spin_lock(&emlog_info_list_lock); // Peeba
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for (einfo = emlog_info_list; einfo != NULL; einfo = einfo->next)
if (einfo->i_ino == inode->i_ino && einfo->i_rdev == inode->i_rdev)
if (einfo->i_ino == inode->i_ino && einfo->i_rdev == inode->i_rdev) {
spin_unlock(&emlog_info_list_lock); // Peeba
return einfo;
}
spin_unlock(&emlog_info_list_lock); // Peeba

return NULL;
}
Expand Down Expand Up @@ -144,8 +149,10 @@ static int create_einfo(const struct inode *inode, int minor,
goto data_malloc_failed;

/* add it to our linked list */
spin_lock(&emlog_info_list_lock); // P714a
einfo->next = emlog_info_list;
emlog_info_list = einfo;
spin_unlock(&emlog_info_list_lock); // P714a

if (emlog_debug)
pr_debug("allocating resources associated with inode %ld.\n", einfo->i_ino);
Expand Down Expand Up @@ -184,6 +191,7 @@ static void free_einfo(struct emlog_info *einfo)
/* now delete the 'einfo' structure from the linked list. 'ptr' is
* the pointer that needs to be changed... which is either the list
* head or one of the 'next' pointers on the list. */
spin_lock(&emlog_info_list_lock); // P714a
ptr = &emlog_info_list;
while (*ptr != einfo) {
if (!*ptr) {
Expand All @@ -194,6 +202,7 @@ static void free_einfo(struct emlog_info *einfo)

}
*ptr = einfo->next;
spin_unlock(&emlog_info_list_lock); // P714a

}

Expand Down Expand Up @@ -516,6 +525,8 @@ static int __init emlog_init(void)
ret_val = -5; goto emlog_init_error;
}

spin_lock_init(&emlog_info_list_lock); // P714a

goto emlog_init_okay;
emlog_init_error:
if (emlog_dev_reg) device_destroy(emlog_class, emlog_dev_type);
Expand Down