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Restructure pipe_read in order to eliminate several race conditions.

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Submitted by:	Matthew Dillon <dillon@apollo.backplane.com> and myself
This commit is contained in:
Alan Cox 1999-06-05 03:53:57 +00:00
parent 8759eb5c80
commit 3d41489171
1 changed files with 47 additions and 69 deletions
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116
sys/kern/sys_pipe.c
View File

@ -16,7 +16,7 @@
* 4. Modifications may be freely made to this file if the above conditions
* are met.
*
* $Id: sys_pipe.c,v 1.50 1999/02/04 23:50:49 dillon Exp $
* $Id: sys_pipe.c,v 1.51 1999/04/04 21:41:15 dt Exp $
*/
/*
@ -327,11 +327,15 @@ pipe_read(fp, uio, cred, flags)
{
struct pipe *rpipe = (struct pipe *) fp->f_data;
int error = 0;
int error;
int nread = 0;
u_int size;
++rpipe->pipe_busy;
error = pipelock(rpipe, 1);
if (error)
goto unlocked_error;
while (uio->uio_resid) {
/*
* normal pipe buffer receive
@ -342,11 +346,9 @@ pipe_read(fp, uio, cred, flags)
size = rpipe->pipe_buffer.cnt;
if (size > (u_int) uio->uio_resid)
size = (u_int) uio->uio_resid;
if ((error = pipelock(rpipe,1)) == 0) {
error = uiomove( &rpipe->pipe_buffer.buffer[rpipe->pipe_buffer.out],
error = uiomove(&rpipe->pipe_buffer.buffer[rpipe->pipe_buffer.out],
size, uio);
pipeunlock(rpipe);
}
if (error) {
break;
}
@ -355,21 +357,29 @@ pipe_read(fp, uio, cred, flags)
rpipe->pipe_buffer.out = 0;
rpipe->pipe_buffer.cnt -= size;
/*
* If there is no more to read in the pipe, reset
* its pointers to the beginning. This improves
* cache hit stats.
*/
if (rpipe->pipe_buffer.cnt == 0) {
rpipe->pipe_buffer.in = 0;
rpipe->pipe_buffer.out = 0;
}
nread += size;
#ifndef PIPE_NODIRECT
/*
* Direct copy, bypassing a kernel buffer.
*/
} else if ((size = rpipe->pipe_map.cnt) &&
(rpipe->pipe_state & PIPE_DIRECTW)) {
caddr_t va;
(rpipe->pipe_state & PIPE_DIRECTW)) {
caddr_t va;
if (size > (u_int) uio->uio_resid)
size = (u_int) uio->uio_resid;
if ((error = pipelock(rpipe,1)) == 0) {
va = (caddr_t) rpipe->pipe_map.kva + rpipe->pipe_map.pos;
error = uiomove(va, size, uio);
pipeunlock(rpipe);
}
va = (caddr_t) rpipe->pipe_map.kva + rpipe->pipe_map.pos;
error = uiomove(va, size, uio);
if (error)
break;
nread += size;
@ -381,32 +391,6 @@ pipe_read(fp, uio, cred, flags)
}
#endif
} else {
/*
* If there is no more to read in the pipe, reset
* its pointers to the beginning. This improves
* cache hit stats.
*
* We get this over with now because it may block
* and cause the state to change out from under us,
* rather then have to re-test the state both before
* and after this fragment.
*/
if ((error = pipelock(rpipe,1)) == 0) {
if (rpipe->pipe_buffer.cnt == 0) {
rpipe->pipe_buffer.in = 0;
rpipe->pipe_buffer.out = 0;
}
pipeunlock(rpipe);
/*
* If pipe filled up due to pipelock
* blocking, loop back up.
*/
if (rpipe->pipe_buffer.cnt > 0)
continue;
}
/*
* detect EOF condition
*/
@ -424,55 +408,49 @@ pipe_read(fp, uio, cred, flags)
}
/*
* break if error (signal via pipelock), or if some
* data was read
* Break if some data was read.
*/
if (error || nread > 0)
if (nread > 0)
break;
/*
* Handle non-blocking mode operation
* Unlock the pipe buffer for our remaining processing. We
* will either break out with an error or we will sleep and
* relock to loop.
*/
pipeunlock(rpipe);
if (fp->f_flag & FNONBLOCK) {
/*
* Handle non-blocking mode operation or
* wait for more data.
*/
if (fp->f_flag & FNONBLOCK)
error = EAGAIN;
break;
}
/*
* Wait for more data
*/
rpipe->pipe_state |= PIPE_WANTR;
if ((error = tsleep(rpipe, PRIBIO|PCATCH, "piperd", 0)) != 0) {
break;
else {
rpipe->pipe_state |= PIPE_WANTR;
if ((error = tsleep(rpipe, PRIBIO|PCATCH, "piperd", 0)) == 0)
error = pipelock(rpipe, 1);
}
if (error)
goto unlocked_error;
}
}
pipeunlock(rpipe);
if (error == 0)
getnanotime(&rpipe->pipe_atime);
unlocked_error:
--rpipe->pipe_busy;
/*
* PIPE_WANT processing only makes sense if pipe_busy is 0.
*/
if ((rpipe->pipe_busy == 0) && (rpipe->pipe_state & PIPE_WANT)) {
rpipe->pipe_state &= ~(PIPE_WANT|PIPE_WANTW);
wakeup(rpipe);
} else if (rpipe->pipe_buffer.cnt < MINPIPESIZE) {
/*
* If there is no more to read in the pipe, reset
* its pointers to the beginning. This improves
* cache hit stats.
*/
if (rpipe->pipe_buffer.cnt == 0) {
if ((error == 0) && (error = pipelock(rpipe,1)) == 0) {
rpipe->pipe_buffer.in = 0;
rpipe->pipe_buffer.out = 0;
pipeunlock(rpipe);
}
}
/*
* If the "write-side" has been blocked, wake it up now.
* Handle write blocking hysteresis.
*/
if (rpipe->pipe_state & PIPE_WANTW) {
rpipe->pipe_state &= ~PIPE_WANTW;