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v9fs_walk() utilizes the v9fs_co_run_in_worker({...}) macro to run the
supplied fs driver code block on a background worker thread.
When either the 'Twalk' client request was interrupted or if the client
requested fid for that 'Twalk' request caused a stat error then that
fs driver code block was left by 'break' keyword, with the intention to
return from worker thread back to main thread as well:
v9fs_co_run_in_worker({
if (v9fs_request_cancelled(pdu)) {
err = -EINTR;
break;
}
err = s->ops->lstat(&s->ctx, &dpath, &fidst);
if (err < 0) {
err = -errno;
break;
}
...
});
However that 'break;' statement also skipped the v9fs_co_run_in_worker()
macro's final and mandatory
/* re-enter back to qemu thread */
qemu_coroutine_yield();
call and thus caused the rest of v9fs_walk() to be continued being
executed on the worker thread instead of main thread, eventually
leading to a crash in the transport virtio transport driver.
To fix this issue and to prevent the same error from happening again by
other users of v9fs_co_run_in_worker() in future, auto wrap the supplied
code block into its own
do { } while (0);
loop inside the 'v9fs_co_run_in_worker' macro definition.
Full discussion and backtrace:
https://lists.gnu.org/archive/html/qemu-devel/2021-08/msg05209.html
https://lists.gnu.org/archive/html/qemu-devel/2021-09/msg00174.html
Fixes: 8d6cb10073
Signed-off-by: Christian Schoenebeck <qemu_oss@crudebyte.com>
Cc: qemu-stable@nongnu.org
Reviewed-by: Greg Kurz <groug@kaod.org>
Message-Id: <E1mLTBg-0002Bh-2D@lizzy.crudebyte.com>
114 lines
5.9 KiB
C
114 lines
5.9 KiB
C
/*
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* 9p backend
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*
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* Copyright IBM, Corp. 2010
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*
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* Authors:
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* Harsh Prateek Bora <harsh@linux.vnet.ibm.com>
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* Venkateswararao Jujjuri(JV) <jvrao@linux.vnet.ibm.com>
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*
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* This work is licensed under the terms of the GNU GPL, version 2. See
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* the COPYING file in the top-level directory.
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*
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*/
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#ifndef QEMU_9P_COTH_H
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#define QEMU_9P_COTH_H
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#include "qemu/thread.h"
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#include "qemu/coroutine.h"
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#include "9p.h"
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/**
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* we want to use bottom half because we want to make sure the below
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* sequence of events.
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*
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* 1. Yield the coroutine in the QEMU thread.
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* 2. Submit the coroutine to a worker thread.
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* 3. Enter the coroutine in the worker thread.
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* we cannot swap step 1 and 2, because that would imply worker thread
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* can enter coroutine while step1 is still running
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*
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* @b PERFORMANCE @b CONSIDERATIONS: As a rule of thumb, keep in mind
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* that hopping between threads adds @b latency! So when handling a
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* 9pfs request, avoid calling v9fs_co_run_in_worker() too often, because
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* this might otherwise sum up to a significant, huge overall latency for
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* providing the response for just a single request. For that reason it
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* is highly recommended to fetch all data from fs driver with a single
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* fs driver request on a background I/O thread (bottom half) in one rush
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* first and then eventually assembling the final response from that data
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* on main I/O thread (top half).
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*/
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#define v9fs_co_run_in_worker(code_block) \
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do { \
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QEMUBH *co_bh; \
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co_bh = qemu_bh_new(co_run_in_worker_bh, \
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qemu_coroutine_self()); \
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qemu_bh_schedule(co_bh); \
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/* \
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* yield in qemu thread and re-enter back \
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* in worker thread \
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*/ \
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qemu_coroutine_yield(); \
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qemu_bh_delete(co_bh); \
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do { \
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code_block; \
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} while (0); \
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/* re-enter back to qemu thread */ \
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qemu_coroutine_yield(); \
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} while (0)
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void co_run_in_worker_bh(void *);
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int coroutine_fn v9fs_co_readlink(V9fsPDU *, V9fsPath *, V9fsString *);
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int coroutine_fn v9fs_co_readdir(V9fsPDU *, V9fsFidState *, struct dirent **);
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int coroutine_fn v9fs_co_readdir_many(V9fsPDU *, V9fsFidState *,
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struct V9fsDirEnt **, off_t, int32_t,
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bool);
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off_t coroutine_fn v9fs_co_telldir(V9fsPDU *, V9fsFidState *);
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void coroutine_fn v9fs_co_seekdir(V9fsPDU *, V9fsFidState *, off_t);
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void coroutine_fn v9fs_co_rewinddir(V9fsPDU *, V9fsFidState *);
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int coroutine_fn v9fs_co_statfs(V9fsPDU *, V9fsPath *, struct statfs *);
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int coroutine_fn v9fs_co_lstat(V9fsPDU *, V9fsPath *, struct stat *);
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int coroutine_fn v9fs_co_chmod(V9fsPDU *, V9fsPath *, mode_t);
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int coroutine_fn v9fs_co_utimensat(V9fsPDU *, V9fsPath *, struct timespec [2]);
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int coroutine_fn v9fs_co_chown(V9fsPDU *, V9fsPath *, uid_t, gid_t);
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int coroutine_fn v9fs_co_truncate(V9fsPDU *, V9fsPath *, off_t);
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int coroutine_fn v9fs_co_llistxattr(V9fsPDU *, V9fsPath *, void *, size_t);
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int coroutine_fn v9fs_co_lgetxattr(V9fsPDU *, V9fsPath *,
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V9fsString *, void *, size_t);
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int coroutine_fn v9fs_co_mknod(V9fsPDU *, V9fsFidState *, V9fsString *, uid_t,
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gid_t, dev_t, mode_t, struct stat *);
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int coroutine_fn v9fs_co_mkdir(V9fsPDU *, V9fsFidState *, V9fsString *,
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mode_t, uid_t, gid_t, struct stat *);
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int coroutine_fn v9fs_co_remove(V9fsPDU *, V9fsPath *);
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int coroutine_fn v9fs_co_rename(V9fsPDU *, V9fsPath *, V9fsPath *);
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int coroutine_fn v9fs_co_unlinkat(V9fsPDU *, V9fsPath *, V9fsString *,
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int flags);
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int coroutine_fn v9fs_co_renameat(V9fsPDU *, V9fsPath *, V9fsString *,
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V9fsPath *, V9fsString *);
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int coroutine_fn v9fs_co_fstat(V9fsPDU *, V9fsFidState *, struct stat *);
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int coroutine_fn v9fs_co_opendir(V9fsPDU *, V9fsFidState *);
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int coroutine_fn v9fs_co_open(V9fsPDU *, V9fsFidState *, int);
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int coroutine_fn v9fs_co_open2(V9fsPDU *, V9fsFidState *, V9fsString *,
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gid_t, int, int, struct stat *);
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int coroutine_fn v9fs_co_lsetxattr(V9fsPDU *, V9fsPath *, V9fsString *,
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void *, size_t, int);
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int coroutine_fn v9fs_co_lremovexattr(V9fsPDU *, V9fsPath *, V9fsString *);
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int coroutine_fn v9fs_co_closedir(V9fsPDU *, V9fsFidOpenState *);
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int coroutine_fn v9fs_co_close(V9fsPDU *, V9fsFidOpenState *);
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int coroutine_fn v9fs_co_fsync(V9fsPDU *, V9fsFidState *, int);
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int coroutine_fn v9fs_co_symlink(V9fsPDU *, V9fsFidState *, V9fsString *,
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const char *, gid_t, struct stat *);
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int coroutine_fn v9fs_co_link(V9fsPDU *, V9fsFidState *,
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V9fsFidState *, V9fsString *);
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int coroutine_fn v9fs_co_pwritev(V9fsPDU *, V9fsFidState *,
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struct iovec *, int, int64_t);
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int coroutine_fn v9fs_co_preadv(V9fsPDU *, V9fsFidState *,
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struct iovec *, int, int64_t);
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int coroutine_fn v9fs_co_name_to_path(V9fsPDU *, V9fsPath *,
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const char *, V9fsPath *);
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int coroutine_fn v9fs_co_st_gen(V9fsPDU *pdu, V9fsPath *path, mode_t,
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V9fsStatDotl *v9stat);
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#endif
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