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| author | Bryce Kwon <bryce@brycekwon.com> | |
|---|---|---|
| committer | Bryce Kwon <bryce@brycekwon.com> | |
| commit | ||
| parent | ||
| tree | ||
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Lock a cache slot with flock
The slot lock was a POSIX record lock, which a process loses the moment
any descriptor on the file closes, and the fill puts the lock file on
stdout, which every exec filter and snapshot compressor closes with its
dup2. A second request on the slot could then rebuild it under the first
and splice the two pages. An flock holds until the last descriptor goes.
Diffstat (limited to 'source')
| -rw-r--r-- | source/cache.c | 13 |
1 file changed, 6 insertions, 7 deletions
diff --git a/source/cache.c b/source/cache.c index 82b3aad..9594fd6 100644 --- a/source/cache.c +++ b/source/cache.c @@ -13,6 +13,7 @@ #include "cgit.h" #include "html.h" #include "shared.h" +#include <sys/file.h> #ifdef HAVE_LINUX_SENDFILE #include <sys/sendfile.h> #endif @@ -232,18 +233,16 @@ static int close_lock(struct cache_slot *slot) */ static int lock_slot(struct cache_slot *slot) { - struct flock lock = { - .l_type = F_WRLCK, - .l_whence = SEEK_SET, - .l_start = 0, - .l_len = 0, - }; struct stat held, named; slot->lock_fd = open(slot->lock_path, O_RDWR | O_CREAT, S_IRUSR | S_IWUSR); if (slot->lock_fd == -1) return errno; - if (fcntl(slot->lock_fd, F_SETLK, &lock) < 0) { + // An flock rather than a POSIX record lock. The descriptor is put on + // stdout for the fill, and a record lock is dropped as soon as any + // descriptor on the file closes, which an exec filter does to stdout, + // while an flock holds until the last descriptor closes. + if (flock(slot->lock_fd, LOCK_EX | LOCK_NB) < 0) { int saved_errno = errno; close(slot->lock_fd); slot->lock_fd = -1; |