87 lines
2.7 KiB
Diff
87 lines
2.7 KiB
Diff
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From d03594b0313db71413b9dcb040f8d5c4da7213b1 Mon Sep 17 00:00:00 2001
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From: David Sterba <dsterba@suse.com>
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Date: Thu, 18 Apr 2024 18:24:48 +0800
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Subject: [PATCH] fix exclusive op enqueue timeout
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There's a report that 'btrfs balance start --enqueue' does not properly
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wait when there are multiple instances started. The command does a busy
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wait instead of timeouts.
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Strace output:
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0.000006 pselect6(5, NULL, NULL, [4], {tv_sec=60, tv_nsec=0}, NULL) = 1 (except [4], left {tv_sec=59, tv_nsec=999999716})
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0.000008 pselect6(5, NULL, NULL, [4], {tv_sec=29, tv_nsec=999999000}, NULL) = 1 (except [4], left {tv_sec=29, tv_nsec=999998786})
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After the first select there's almost the entire time left, the second
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one starts right after it.
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Polling/selecting sysfs files is possible under some conditions:
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- the file descriptor must be reopened before each poll/select
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- the whole buffer must be read too
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With that in place it now works as expected. The remaining timeout logic
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is slightly adjusted to wait at most 10 seconds so the pending jobs do
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not wait too long if there's still a lot of time left from the first
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select.
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Issue: #746
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Signed-off-by: David Sterba <dsterba@suse.com>
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---
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common/utils.c | 21 ++++++++++++++++++++-
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1 file changed, 20 insertions(+), 1 deletion(-)
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diff --git a/common/utils.c b/common/utils.c
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index 62f0e3f..7cde492 100644
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--- a/common/utils.c
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+++ b/common/utils.c
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@@ -1326,26 +1326,45 @@ int check_running_fs_exclop(int fd, enum exclusive_operation start, bool enqueue
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fflush(stdout);
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}
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+ /*
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+ * The sysfs file descriptor needs to be reopened and all data read
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+ * before each select().
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+ */
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while (exclop > 0) {
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fd_set fds;
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struct timeval tv = { .tv_sec = 60, .tv_usec = 0 };
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+ char tmp[1024];
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+ close(sysfs_fd);
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+ sysfs_fd = sysfs_open_fsid_file(fd, "exclusive_operation");
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+ if (sysfs_fd < 0)
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+ return sysfs_fd;
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FD_ZERO(&fds);
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FD_SET(sysfs_fd, &fds);
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+ ret = read(sysfs_fd, tmp, sizeof(tmp));
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ret = select(sysfs_fd + 1, NULL, NULL, &fds, &tv);
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if (ret < 0) {
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ret = -errno;
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break;
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}
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if (ret > 0) {
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+ close(sysfs_fd);
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+ sysfs_fd = sysfs_open_fsid_file(fd, "exclusive_operation");
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+ if (sysfs_fd < 0)
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+ return sysfs_fd;
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+
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+ FD_ZERO(&fds);
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+ FD_SET(sysfs_fd, &fds);
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+
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+ ret = read(sysfs_fd, tmp, sizeof(tmp));
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/*
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* Notified before the timeout, check again before
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* returning. In case there are more operations
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* waiting, we want to reduce the chances to race so
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* reuse the remaining time to randomize the order.
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*/
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- tv.tv_sec /= 2;
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+ tv.tv_sec = (tv.tv_sec % 10) + 1;
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ret = select(sysfs_fd + 1, NULL, NULL, &fds, &tv);
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exclop = get_fs_exclop(fd);
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if (exclop <= 0)
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--
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2.43.0
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