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udev-watch: retry to save watch handle with random delay

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Also, remove the watch handle if we cannot save it.
This commit is contained in:
Yu Watanabe 2021-09-12 15:49:22 +09:00
parent 20ec7d9ed5
commit 2d3af41f0e
1 changed files with 41 additions and 4 deletions
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45
src/udev/udev-watch.c
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@ -12,8 +12,13 @@
#include "dirent-util.h"
#include "fs-util.h"
#include "parse-util.h"
#include "random-util.h"
#include "udev-watch.h"
#define SAVE_WATCH_HANDLE_MAX_RETRIES 128
#define MAX_RANDOM_DELAY (100 * USEC_PER_MSEC)
#define MIN_RANDOM_DELAY ( 10 * USEC_PER_MSEC)
int udev_watch_restore(int inotify_fd) {
struct dirent *ent;
DIR *dir;
@ -93,11 +98,43 @@ int udev_watch_begin(int inotify_fd, sd_device *dev) {
return ignore ? 0 : r;
}
r = device_set_watch_handle(dev, wd);
if (r < 0)
return log_device_warning_errno(dev, r, "Failed to save watch handle in /run/udev/watch: %m");
for (unsigned i = 0; i < SAVE_WATCH_HANDLE_MAX_RETRIES; i++) {
if (i > 0) {
usec_t delay = MIN_RANDOM_DELAY + random_u64_range(MAX_RANDOM_DELAY - MIN_RANDOM_DELAY);
return 0;
/* When the same handle is reused for different device node, we may fail to
* save the watch handle with -EEXIST. Let's consider the case of two workers A
* and B do the following:
*
* 1. A calls inotify_rm_watch()
* 2. B calls inotify_add_watch()
* 3. B calls device_set_watch_handle()
* 4. A calls device_set_watch_handle(-1)
*
* At step 3, the old symlinks to save the watch handle still exist. So,
* device_set_watch_handle() fails with -EEXIST. */
log_device_debug_errno(dev, r,
"Failed to save watch handle '%i' for %s in "
"/run/udev/watch, retrying in after %s: %m",
wd, devnode, FORMAT_TIMESPAN(delay, USEC_PER_MSEC));
(void) usleep(delay);
}
r = device_set_watch_handle(dev, wd);
if (r >= 0)
return 0;
if (r != -EEXIST)
break;
}
log_device_warning_errno(dev, r,
"Failed to save watch handle '%i' for %s in /run/udev/watch: %m",
wd, devnode);
(void) inotify_rm_watch(inotify_fd, wd);
return r;
}
int udev_watch_end(int inotify_fd, sd_device *dev) {