147 lines
6.3 KiB
Diff
147 lines
6.3 KiB
Diff
From 16a6007cc8881ef19cc97de676d3b2b36b2def82 Mon Sep 17 00:00:00 2001
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From: Yu Watanabe <watanabe.yu+github@gmail.com>
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Date: Wed, 1 Sep 2021 12:57:40 +0900
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Subject: [PATCH] udev-node: always update timestamp of stack directory
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Please see the comments in the code.
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(cherry picked from commit 6df797f75fa08bb1a9e657001229bd47903e6174)
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Related: #1977994
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---
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src/udev/udev-node.c | 90 ++++++++++++++++++++++++++++++++++++++++++--
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1 file changed, 87 insertions(+), 3 deletions(-)
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diff --git a/src/udev/udev-node.c b/src/udev/udev-node.c
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index 5d6aae0bd4..0de848da19 100644
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--- a/src/udev/udev-node.c
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+++ b/src/udev/udev-node.c
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@@ -32,6 +32,7 @@
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#define CREATE_LINK_MAX_RETRIES 128
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#define LINK_UPDATE_MAX_RETRIES 128
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#define CREATE_STACK_LINK_MAX_RETRIES 128
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+#define UPDATE_TIMESTAMP_MAX_RETRIES 128
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#define UDEV_NODE_HASH_KEY SD_ID128_MAKE(b9,6a,f1,ce,40,31,44,1a,9e,19,ec,8b,ae,f3,e3,2f)
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static int create_symlink(const char *target, const char *slink) {
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@@ -285,9 +286,60 @@ toolong:
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return size - 1;
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}
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+static int update_timestamp(sd_device *dev, const char *path, struct stat *prev) {
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+ assert(path);
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+ assert(prev);
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+
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+ /* Even if a symlink in the stack directory is created/removed, the mtime of the directory may
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+ * not be changed. Why? Let's consider the following situation. For simplicity, let's assume
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+ * there exist three udev workers (A, B, and C) and all of them calls link_update() for the
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+ * same devlink simultaneously.
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+ *
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+ * 1. B creates/removes a symlink in the stack directory.
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+ * 2. A calls the first stat() in the loop of link_update().
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+ * 3. A calls link_find_prioritized().
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+ * 4. C creates/removes another symlink in the stack directory, so the result of the step 3 is outdated.
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+ * 5. B and C finish link_update().
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+ * 6. A creates/removes devlink according to the outdated result in the step 3.
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+ * 7. A calls the second stat() in the loop of link_update().
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+ *
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+ * If these 7 steps are processed in this order within a short time period that kernel's timer
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+ * does not increase, then even if the contents in the stack directory is changed, the results
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+ * of two stat() called by A shows the same timestamp, and A cannot detect the change.
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+ *
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+ * By calling this function after creating/removing symlinks in the stack directory, the
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+ * timestamp of the stack directory is always increased at least in the above step 5, so A can
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+ * detect the update. */
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+
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+ if ((prev->st_mode & S_IFMT) == 0)
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+ return 0; /* Does not exist, or previous stat() failed. */
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+
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+ for (unsigned i = 0; i < UPDATE_TIMESTAMP_MAX_RETRIES; i++) {
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+ struct stat st;
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+
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+ if (stat(path, &st) < 0)
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+ return -errno;
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+
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+ if (!stat_inode_unmodified(prev, &st))
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+ return 0;
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+
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+ log_device_debug(dev,
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+ "%s is modified, but its timestamp is not changed, "
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+ "updating timestamp after 10ms.",
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+ path);
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+
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+ (void) usleep(10 * USEC_PER_MSEC);
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+ if (utimensat(AT_FDCWD, path, NULL, 0) < 0)
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+ return -errno;
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+ }
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+
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+ return -ELOOP;
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+}
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+
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static int update_stack_directory(sd_device *dev, const char *dirname, bool add) {
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_cleanup_free_ char *filename = NULL, *data = NULL, *buf = NULL;
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const char *devname, *id;
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+ struct stat st = {};
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int priority, r;
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assert(dev);
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@@ -302,10 +354,31 @@ static int update_stack_directory(sd_device *dev, const char *dirname, bool add)
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return log_oom_debug();
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if (!add) {
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- if (unlink(filename) < 0 && errno != ENOENT)
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- log_device_debug_errno(dev, errno, "Failed to remove %s, ignoring: %m", filename);
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+ bool unlink_failed = false;
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+
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+ if (stat(dirname, &st) < 0) {
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+ if (errno == ENOENT)
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+ return 0; /* The stack directory is already removed. That's OK. */
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+ log_device_debug_errno(dev, errno, "Failed to stat %s, ignoring: %m", dirname);
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+ }
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+
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+ if (unlink(filename) < 0) {
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+ unlink_failed = true;
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+ if (errno != ENOENT)
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+ log_device_debug_errno(dev, errno, "Failed to remove %s, ignoring: %m", filename);
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+ }
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+
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+ if (rmdir(dirname) >= 0 || errno == ENOENT)
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+ return 0;
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+
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+ if (unlink_failed)
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+ return 0; /* If we failed to remove the symlink, there is almost nothing we can do. */
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+
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+ /* The symlink was removed. Check if the timestamp of directory is changed. */
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+ r = update_timestamp(dev, dirname, &st);
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+ if (r < 0 && r != -ENOENT)
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+ return log_device_debug_errno(dev, r, "Failed to update timestamp of %s: %m", dirname);
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- (void) rmdir(dirname);
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return 0;
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}
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@@ -335,12 +408,23 @@ static int update_stack_directory(sd_device *dev, const char *dirname, bool add)
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if (r < 0)
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return log_device_debug_errno(dev, r, "Failed to create directory %s: %m", dirname);
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+ if (stat(dirname, &st) < 0) {
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+ if (errno == ENOENT)
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+ continue;
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+ return log_device_debug_errno(dev, errno, "Failed to stat %s: %m", dirname);
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+ }
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+
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if (symlink(data, filename) < 0) {
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if (errno == ENOENT)
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continue;
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return log_device_debug_errno(dev, errno, "Failed to create symbolic link %s: %m", filename);
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}
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+ /* The symlink was created. Check if the timestamp of directory is changed. */
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+ r = update_timestamp(dev, dirname, &st);
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+ if (r < 0)
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+ return log_device_debug_errno(dev, r, "Failed to update timestamp of %s: %m", dirname);
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+
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return 0;
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}
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