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Preallocate a struct file as the first thing in falloc() before we lock

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the filelist_lock and check nfiles.  This closes a race where we had to
unlock the filedesc to re-lock the filelist_lock.

Reported by:	David Xu
Reviewed by:	bde (mostly)
This commit is contained in:
John Baldwin 2002-07-17 02:48:43 +00:00
parent 627ed43ba7
commit 3d3f20cbe6
1 changed files with 5 additions and 16 deletions
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21
sys/kern/kern_descrip.c
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@ -1107,32 +1107,24 @@ falloc(td, resultfp, resultfd)
register struct file *fp, *fq;
int error, i;
fp = uma_zalloc(file_zone, M_WAITOK | M_ZERO);
sx_xlock(&filelist_lock);
if (nfiles >= maxfiles) {
sx_xunlock(&filelist_lock);
uma_zfree(file_zone, fp);
tablefull("file");
return (ENFILE);
}
nfiles++;
sx_xunlock(&filelist_lock);
/*
* Allocate a new file descriptor.
* If the process has file descriptor zero open, add to the list
* of open files at that point, otherwise put it at the front of
* the list of open files.
*/
fp = uma_zalloc(file_zone, M_WAITOK);
bzero(fp, sizeof(*fp));
/*
* wait until after malloc (which may have blocked) returns before
* allocating the slot, else a race might have shrunk it if we had
* allocated it before the malloc.
* If the process has file descriptor zero open, add the new file
* descriptor to the list of open files at that point, otherwise
* put it at the front of the list of open files.
*/
FILEDESC_LOCK(p->p_fd);
if ((error = fdalloc(td, 0, &i))) {
FILEDESC_UNLOCK(p->p_fd);
sx_xlock(&filelist_lock);
nfiles--;
sx_xunlock(&filelist_lock);
uma_zfree(file_zone, fp);
@ -1144,9 +1136,6 @@ falloc(td, resultfp, resultfd)
fp->f_cred = crhold(td->td_ucred);
fp->f_ops = &badfileops;
fp->f_seqcount = 1;
FILEDESC_UNLOCK(p->p_fd);
sx_xlock(&filelist_lock);
FILEDESC_LOCK(p->p_fd);
if ((fq = p->p_fd->fd_ofiles[0])) {
LIST_INSERT_AFTER(fq, fp, f_list);
} else {