diff options
author | Toby Gray <toby.gray@realvnc.com> | 2012-05-03 11:25:11 +0100 |
---|---|---|
committer | Pete Batard <pete@akeo.ie> | 2012-05-03 21:54:07 +0100 |
commit | 1ed09c7b2a5fc27c3cfea21740584879781bff67 (patch) | |
tree | 621da73f9bdf7c4f2df10583ab109c14665d8fb4 | |
parent | 939a4782b28c36dfddb68585c4b027a4d5494a5b (diff) | |
download | libusb-1ed09c7b2a5fc27c3cfea21740584879781bff67.tar.gz |
Windows: Fix deadlock in backend when submitting transfers.
Without this change the Windows backend needed to call usbi_fd_notification()
from within the backend's submit_transfer. This can cause deadlock when
attempting to lock the event lock if another thread was processing events on
the just-submitted transfer.
The deadlock comes about as the thread calling libusb_submit_transfer acquires
the transfer mutex before trying to acquire the event lock; this is the other
order of lock acquisition from an event thread handling activity on the just
submitted transfer. This could lead to one of two deadlocks:
1) If the transfer completes while usbi_fd_notification() is waiting for
the event lock and the callback attempts to resubmit the transfer.
2) If the transfer timeout is hit while usbi_fd_notification() is waiting
for the event lock then the attempt to cancel the transfer will deadlock.
This patch fixes both of these deadlocks by having libusb_submit_transfer()
only call usbi_fd_notification() after having released the transfer mutex.
-rw-r--r-- | libusb/io.c | 4 | ||||
-rw-r--r-- | libusb/libusbi.h | 3 | ||||
-rw-r--r-- | libusb/os/windows_usb.c | 6 | ||||
-rw-r--r-- | libusb/version.h | 2 |
4 files changed, 11 insertions, 4 deletions
diff --git a/libusb/io.c b/libusb/io.c index d7fae7e..ab32e70 100644 --- a/libusb/io.c +++ b/libusb/io.c @@ -1292,6 +1292,7 @@ int API_EXPORTED libusb_submit_transfer(struct libusb_transfer *transfer) LIBUSB_TRANSFER_TO_USBI_TRANSFER(transfer); int r; int first; + int updated_fds; usbi_mutex_lock(&itransfer->lock); itransfer->transferred = 0; @@ -1325,7 +1326,10 @@ int API_EXPORTED libusb_submit_transfer(struct libusb_transfer *transfer) #endif out: + updated_fds = (itransfer->flags & USBI_TRANSFER_UPDATED_FDS); usbi_mutex_unlock(&itransfer->lock); + if (updated_fds) + usbi_fd_notification(ctx); return r; } diff --git a/libusb/libusbi.h b/libusb/libusbi.h index c3d2158..0aa6bf9 100644 --- a/libusb/libusbi.h +++ b/libusb/libusbi.h @@ -347,6 +347,9 @@ enum usbi_transfer_flags { /* Operation on the transfer failed because the device disappeared */ USBI_TRANSFER_DEVICE_DISAPPEARED = 1 << 3, + + /* Set by backend submit_transfer() if the fds in use have been updated */ + USBI_TRANSFER_UPDATED_FDS = 1 << 4, }; #define USBI_TRANSFER_TO_LIBUSB_TRANSFER(transfer) \ diff --git a/libusb/os/windows_usb.c b/libusb/os/windows_usb.c index 1957964..f29f84c 100644 --- a/libusb/os/windows_usb.c +++ b/libusb/os/windows_usb.c @@ -1770,7 +1770,7 @@ static int submit_bulk_transfer(struct usbi_transfer *itransfer) usbi_add_pollfd(ctx, transfer_priv->pollable_fd.fd, (short)(IS_XFERIN(transfer) ? POLLIN : POLLOUT)); - usbi_fd_notification(ctx); + itransfer->flags |= USBI_TRANSFER_UPDATED_FDS; return LIBUSB_SUCCESS; } @@ -1790,7 +1790,7 @@ static int submit_iso_transfer(struct usbi_transfer *itransfer) usbi_add_pollfd(ctx, transfer_priv->pollable_fd.fd, (short)(IS_XFERIN(transfer) ? POLLIN : POLLOUT)); - usbi_fd_notification(ctx); + itransfer->flags |= USBI_TRANSFER_UPDATED_FDS; return LIBUSB_SUCCESS; } @@ -1809,7 +1809,7 @@ static int submit_control_transfer(struct usbi_transfer *itransfer) usbi_add_pollfd(ctx, transfer_priv->pollable_fd.fd, POLLIN); - usbi_fd_notification(ctx); + itransfer->flags |= USBI_TRANSFER_UPDATED_FDS; return LIBUSB_SUCCESS; } diff --git a/libusb/version.h b/libusb/version.h index ef81eba..c0df768 100644 --- a/libusb/version.h +++ b/libusb/version.h @@ -9,7 +9,7 @@ #define LIBUSB_MICRO 10 #endif #ifndef LIBUSB_NANO -#define LIBUSB_NANO 10488 +#define LIBUSB_NANO 10489 #endif /* LIBUSB_RC is the release candidate suffix. Should normally be empty. */ #ifndef LIBUSB_RC |