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author | Herbert Xu <herbert@gondor.apana.org.au> | 2006-01-06 00:09:47 -0800 |
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committer | Linus Torvalds <torvalds@g5.osdl.org> | 2006-01-06 08:33:20 -0800 |
commit | 4b2f0260c74324abca76ccaa42d426af163125e7 (patch) | |
tree | 881f76200dc3489b11497528feb72d6eae93bddb /include/linux/nbd.h | |
parent | bd6a59b22fd3bd044bb14978b885bcd042a10e8e (diff) | |
download | kernel_samsung_espresso10-4b2f0260c74324abca76ccaa42d426af163125e7.zip kernel_samsung_espresso10-4b2f0260c74324abca76ccaa42d426af163125e7.tar.gz kernel_samsung_espresso10-4b2f0260c74324abca76ccaa42d426af163125e7.tar.bz2 |
[PATCH] nbd: fix TX/RX race condition
Janos Haar of First NetCenter Bt. reported numerous crashes involving the
NBD driver. With his help, this was tracked down to bogus bio vectors
which in turn was the result of a race condition between the
receive/transmit routines in the NBD driver.
The bug manifests itself like this:
CPU0 CPU1
do_nbd_request
add req to queuelist
nbd_send_request
send req head
for each bio
kmap
send
nbd_read_stat
nbd_find_request
nbd_end_request
kunmap
When CPU1 finishes nbd_end_request, the request and all its associated
bio's are freed. So when CPU0 calls kunmap whose argument is derived from
the last bio, it may crash.
Under normal circumstances, the race occurs only on the last bio. However,
if an error is encountered on the remote NBD server (such as an incorrect
magic number in the request), or if there were a bug in the server, it is
possible for the nbd_end_request to occur any time after the request's
addition to the queuelist.
The following patch fixes this problem by making sure that requests are not
added to the queuelist until after they have been completed transmission.
In order for the receiving side to be ready for responses involving
requests still being transmitted, the patch introduces the concept of the
active request.
When a response matches the current active request, its processing is
delayed until after the tranmission has come to a stop.
This has been tested by Janos and it has been successful in curing this
race condition.
From: Herbert Xu <herbert@gondor.apana.org.au>
Here is an updated patch which removes the active_req wait in
nbd_clear_queue and the associated memory barrier.
I've also clarified this in the comment.
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Cc: <djani22@dynamicweb.hu>
Cc: Paul Clements <Paul.Clements@SteelEye.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'include/linux/nbd.h')
-rw-r--r-- | include/linux/nbd.h | 8 |
1 files changed, 8 insertions, 0 deletions
diff --git a/include/linux/nbd.h b/include/linux/nbd.h index 090e210..f95d51f 100644 --- a/include/linux/nbd.h +++ b/include/linux/nbd.h @@ -37,18 +37,26 @@ enum { /* userspace doesn't need the nbd_device structure */ #ifdef __KERNEL__ +#include <linux/wait.h> + /* values for flags field */ #define NBD_READ_ONLY 0x0001 #define NBD_WRITE_NOCHK 0x0002 +struct request; + struct nbd_device { int flags; int harderror; /* Code of hard error */ struct socket * sock; struct file * file; /* If == NULL, device is not ready, yet */ int magic; + spinlock_t queue_lock; struct list_head queue_head;/* Requests are added here... */ + struct request *active_req; + wait_queue_head_t active_wq; + struct semaphore tx_lock; struct gendisk *disk; int blksize; |