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authorMiklos Szeredi <miklos@szeredi.hu>2006-06-25 08:48:50 -0400
committerLinus Torvalds <torvalds@g5.osdl.org>2006-06-25 13:01:19 -0400
commit51eb01e73599efb88c6c20b1c226d20309a75450 (patch)
treec37e7a61ce7c049a4615dfb2ee994866d3c85bd6 /Documentation/filesystems/fuse.txt
parent3e8c54fad89144b8d63cc41619f363df1ec7cc42 (diff)
[PATCH] fuse: no backgrounding on interrupt
Don't put requests into the background when a fatal interrupt occurs while the request is in userspace. This removes a major wart from the implementation. Backgrounding of requests was introduced to allow breaking of deadlocks. However now the same can be achieved by aborting the filesystem through the 'abort' sysfs attribute. This is a change in the interface, but should not cause problems, since these kinds of deadlocks never happen during normal operation. Signed-off-by: Miklos Szeredi <miklos@szeredi.hu> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'Documentation/filesystems/fuse.txt')
-rw-r--r--Documentation/filesystems/fuse.txt40
1 files changed, 6 insertions, 34 deletions
diff --git a/Documentation/filesystems/fuse.txt b/Documentation/filesystems/fuse.txt
index 33f74310d161..e7747774ceb9 100644
--- a/Documentation/filesystems/fuse.txt
+++ b/Documentation/filesystems/fuse.txt
@@ -304,25 +304,7 @@ Scenario 1 - Simple deadlock
304 | | for "file"] 304 | | for "file"]
305 | | *DEADLOCK* 305 | | *DEADLOCK*
306 306
307The solution for this is to allow requests to be interrupted while 307The solution for this is to allow the filesystem to be aborted.
308they are in userspace:
309
310 | [interrupted by signal] |
311 | <fuse_unlink() |
312 | [release semaphore] | [semaphore acquired]
313 | <sys_unlink() |
314 | | >fuse_unlink()
315 | | [queue req on fc->pending]
316 | | [wake up fc->waitq]
317 | | [sleep on req->waitq]
318
319If the filesystem daemon was single threaded, this will stop here,
320since there's no other thread to dequeue and execute the request.
321In this case the solution is to kill the FUSE daemon as well. If
322there are multiple serving threads, you just have to kill them as
323long as any remain.
324
325Moral: a filesystem which deadlocks, can soon find itself dead.
326 308
327Scenario 2 - Tricky deadlock 309Scenario 2 - Tricky deadlock
328---------------------------- 310----------------------------
@@ -355,24 +337,14 @@ but is caused by a pagefault.
355 | | [lock page] 337 | | [lock page]
356 | | * DEADLOCK * 338 | | * DEADLOCK *
357 339
358Solution is again to let the the request be interrupted (not 340Solution is basically the same as above.
359elaborated further).
360 341
361An additional problem is that while the write buffer is being 342An additional problem is that while the write buffer is being
362copied to the request, the request must not be interrupted. This 343copied to the request, the request must not be interrupted. This
363is because the destination address of the copy may not be valid 344is because the destination address of the copy may not be valid
364after the request is interrupted. 345after the request is interrupted.
365 346
366This is solved with doing the copy atomically, and allowing 347This is solved with doing the copy atomically, and allowing abort
367interruption while the page(s) belonging to the write buffer are 348while the page(s) belonging to the write buffer are faulted with
368faulted with get_user_pages(). The 'req->locked' flag indicates 349get_user_pages(). The 'req->locked' flag indicates when the copy is
369when the copy is taking place, and interruption is delayed until 350taking place, and abort is delayed until this flag is unset.
370this flag is unset.
371
372Scenario 3 - Tricky deadlock with asynchronous read
373---------------------------------------------------
374
375The same situation as above, except thread-1 will wait on page lock
376and hence it will be uninterruptible as well. The solution is to
377abort the connection with forced umount (if mount is attached) or
378through the abort attribute in sysfs.