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* rds: Integer overflow in RDS cmsg handlingDan Rosenberg2010-11-17
| | | | | | | | | | | | | In rds_cmsg_rdma_args(), the user-provided args->nr_local value is restricted to less than UINT_MAX. This seems to need a tighter upper bound, since the calculation of total iov_size can overflow, resulting in a small sock_kmalloc() allocation. This would probably just result in walking off the heap and crashing when calling rds_rdma_pages() with a high count value. If it somehow doesn't crash here, then memory corruption could occur soon after. Signed-off-by: Dan Rosenberg <drosenberg@vsecurity.com> Signed-off-by: David S. Miller <davem@davemloft.net>
* rds: Fix rds message leak in rds_message_map_pagesPavel Emelyanov2010-11-08
| | | | | | | | The sgs allocation error path leaks the allocated message. Signed-off-by: Pavel Emelyanov <xemul@openvz.org> Acked-by: Andy Grover <andy.grover@oracle.com> Signed-off-by: David S. Miller <davem@davemloft.net>
* rds: Remove kfreed tcp conn from listPavel Emelyanov2010-11-03
| | | | | | | | All the rds_tcp_connection objects are stored list, but when being freed it should be removed from there. Signed-off-by: Pavel Emelyanov <xemul@openvz.org> Signed-off-by: David S. Miller <davem@davemloft.net>
* rds: Lost locking in loop connection freeingPavel Emelyanov2010-11-03
| | | | | | | | The conn is removed from list in there and this requires proper lock protection. Signed-off-by: Pavel Emelyanov <xemul@openvz.org> Signed-off-by: David S. Miller <davem@davemloft.net>
* RDS: Let rds_message_alloc_sgs() return NULLAndy Grover2010-10-30
| | | | | | | | | | | | | | | | | Even with the previous fix, we still are reading the iovecs once to determine SGs needed, and then again later on. Preallocating space for sg lists as part of rds_message seemed like a good idea but it might be better to not do this. While working to redo that code, this patch attempts to protect against userspace rewriting the rds_iovec array between the first and second accesses. The consequences of this would be either a too-small or too-large sg list array. Too large is not an issue. This patch changes all callers of message_alloc_sgs to handle running out of preallocated sgs, and fail gracefully. Signed-off-by: Andy Grover <andy.grover@oracle.com> Signed-off-by: David S. Miller <davem@davemloft.net>
* RDS: Copy rds_iovecs into kernel memory instead of rereading from userspaceAndy Grover2010-10-30
| | | | | | | | | | | | | | | | | | | Change rds_rdma_pages to take a passed-in rds_iovec array instead of doing copy_from_user itself. Change rds_cmsg_rdma_args to copy rds_iovec array once only. This eliminates the possibility of userspace changing it after our sanity checks. Implement stack-based storage for small numbers of iovecs, based on net/socket.c, to save an alloc in the extremely common case. Although this patch reduces iovec copies in cmsg_rdma_args to 1, we still do another one in rds_rdma_extra_size. Getting rid of that one will be trickier, so it'll be a separate patch. Signed-off-by: Andy Grover <andy.grover@oracle.com> Signed-off-by: David S. Miller <davem@davemloft.net>
* RDS: Clean up error handling in rds_cmsg_rdma_argsAndy Grover2010-10-30
| | | | | | | | | | We don't need to set ret = 0 at the end -- it's initialized to 0. Also, don't increment s_send_rdma stat if we're exiting with an error. Signed-off-by: Andy Grover <andy.grover@oracle.com> Signed-off-by: David S. Miller <davem@davemloft.net>
* RDS: Return -EINVAL if rds_rdma_pages returns an errorAndy Grover2010-10-30
| | | | | | | | rds_cmsg_rdma_args would still return success even if rds_rdma_pages returned an error (or overflowed). Signed-off-by: Andy Grover <andy.grover@oracle.com> Signed-off-by: David S. Miller <davem@davemloft.net>
* net: fix rds_iovec page count overflowLinus Torvalds2010-10-30
| | | | | | | | | | | | | | | | | | | As reported by Thomas Pollet, the rdma page counting can overflow. We get the rdma sizes in 64-bit unsigned entities, but then limit it to UINT_MAX bytes and shift them down to pages (so with a possible "+1" for an unaligned address). So each individual page count fits comfortably in an 'unsigned int' (not even close to overflowing into signed), but as they are added up, they might end up resulting in a signed return value. Which would be wrong. Catch the case of tot_pages turning negative, and return the appropriate error code. Reported-by: Thomas Pollet <thomas.pollet@gmail.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Andy Grover <andy.grover@oracle.com> Signed-off-by: David S. Miller <davem@davemloft.net>
* Merge branch 'master' of ↵David S. Miller2010-10-21
|\ | | | | | | | | | | | | master.kernel.org:/pub/scm/linux/kernel/git/davem/net-2.6 Conflicts: net/core/dev.c
| * De-pessimize rds_page_copy_userLinus Torvalds2010-10-15
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Don't try to "optimize" rds_page_copy_user() by using kmap_atomic() and the unsafe atomic user mode accessor functions. It's actually slower than the straightforward code on any reasonable modern CPU. Back when the code was written (although probably not by the time it was actually merged, though), 32-bit x86 may have been the dominant architecture. And there kmap_atomic() can be a lot faster than kmap() (unless you have very good locality, in which case the virtual address caching by kmap() can overcome all the downsides). But these days, x86-64 may not be more populous, but it's getting there (and if you care about performance, it's definitely already there - you'd have upgraded your CPU's already in the last few years). And on x86-64, the non-kmap_atomic() version is faster, simply because the code is simpler and doesn't have the "re-try page fault" case. People with old hardware are not likely to care about RDS anyway, and the optimization for the 32-bit case is simply buggy, since it doesn't verify the user addresses properly. Reported-by: Dan Rosenberg <drosenberg@vsecurity.com> Acked-by: Andrew Morton <akpm@linux-foundation.org> Cc: stable@kernel.org Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
* | rds: make local functions/variables staticstephen hemminger2010-10-21
| | | | | | | | | | | | | | | | | | The RDS protocol has lots of functions that should be declared static. rds_message_get/add_version_extension is removed since it defined but never used. Signed-off-by: Stephen Hemminger <shemminger@vyatta.com> Signed-off-by: David S. Miller <davem@davemloft.net>
* | Merge branch 'master' of ↵David S. Miller2010-09-27
|\| | | | | | | | | | | | | | | master.kernel.org:/pub/scm/linux/kernel/git/davem/net-2.6 Conflicts: drivers/net/qlcnic/qlcnic_init.c net/ipv4/ip_output.c
| * net: fix a lockdep splatEric Dumazet2010-09-25
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | We have for each socket : One spinlock (sk_slock.slock) One rwlock (sk_callback_lock) Possible scenarios are : (A) (this is used in net/sunrpc/xprtsock.c) read_lock(&sk->sk_callback_lock) (without blocking BH) <BH> spin_lock(&sk->sk_slock.slock); ... read_lock(&sk->sk_callback_lock); ... (B) write_lock_bh(&sk->sk_callback_lock) stuff write_unlock_bh(&sk->sk_callback_lock) (C) spin_lock_bh(&sk->sk_slock) ... write_lock_bh(&sk->sk_callback_lock) stuff write_unlock_bh(&sk->sk_callback_lock) spin_unlock_bh(&sk->sk_slock) This (C) case conflicts with (A) : CPU1 [A] CPU2 [C] read_lock(callback_lock) <BH> spin_lock_bh(slock) <wait to spin_lock(slock)> <wait to write_lock_bh(callback_lock)> We have one problematic (C) use case in inet_csk_listen_stop() : local_bh_disable(); bh_lock_sock(child); // spin_lock_bh(&sk->sk_slock) WARN_ON(sock_owned_by_user(child)); ... sock_orphan(child); // write_lock_bh(&sk->sk_callback_lock) lockdep is not happy with this, as reported by Tetsuo Handa It seems only way to deal with this is to use read_lock_bh(callbacklock) everywhere. Thanks to Jarek for pointing a bug in my first attempt and suggesting this solution. Reported-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> Tested-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com> CC: Jarek Poplawski <jarkao2@gmail.com> Tested-by: Eric Dumazet <eric.dumazet@gmail.com> Signed-off-by: David S. Miller <davem@davemloft.net>
* | rds: spin_lock_irq() is not nestableDan Carpenter2010-09-19
| | | | | | | | | | | | | | | | | | This is basically just a cleanup. IRQs were disabled on the previous line so we don't need to do it again here. In the current code IRQs would get turned on one line earlier than intended. Signed-off-by: Dan Carpenter <error27@gmail.com> Signed-off-by: David S. Miller <davem@davemloft.net>
* | rds: double unlock in rds_ib_cm_handle_connect()Dan Carpenter2010-09-19
| | | | | | | | | | | | | | We unlock after we goto out. Signed-off-by: Dan Carpenter <error27@gmail.com> Signed-off-by: David S. Miller <davem@davemloft.net>
* | rds: signedness bugDan Carpenter2010-09-19
| | | | | | | | | | | | | | | | In the original code if the copy_from_user() fails in rds_rdma_pages() then the error handling fails and we get a stack trace from kmalloc(). Signed-off-by: Dan Carpenter <error27@gmail.com> Signed-off-by: David S. Miller <davem@davemloft.net>
* | RDS: Implement masked atomic operationsAndy Grover2010-09-08
| | | | | | | | | | | | | | | | | | Add two CMSGs for masked versions of cswp and fadd. args struct modified to use a union for different atomic op type's arguments. Change IB to do masked atomic ops. Atomic op type in rds_message similarly unionized. Signed-off-by: Andy Grover <andy.grover@oracle.com>
* | RDS/IB: print string constants in more placesZach Brown2010-09-08
| | | | | | | | | | | | | | | | | | This prints the constant identifier for work completion status and rdma cm event types, like we already do for IB event types. A core string array helper is added that each string type uses. Signed-off-by: Zach Brown <zach.brown@oracle.com>
* | RDS: cancel connection work structs as we shut downZach Brown2010-09-08
| | | | | | | | | | | | | | Nothing was canceling the send and receive work that might have been queued as a conn was being destroyed. Signed-off-by: Zach Brown <zach.brown@oracle.com>
* | RDS: don't call rds_conn_shutdown() from rds_conn_destroy()Zach Brown2010-09-08
| | | | | | | | | | | | | | | | | | | | | | | | | | rds_conn_shutdown() can return before the connection is shut down when it encounters an existing state that it doesn't understand. This lets rds_conn_destroy() then start tearing down the conn from under paths that are still using it. It's more reliable the shutdown work and wait for krdsd to complete the shutdown callback. This stopped some hangs I was seeing where krdsd was trying to shut down a freed conn. Signed-off-by: Zach Brown <zach.brown@oracle.com>
* | RDS: have sockets get transport module referencesZach Brown2010-09-08
| | | | | | | | | | | | | | | | | | | | | | | | Right now there's nothing to stop the various paths that use rs->rs_transport from racing with rmmod and executing freed transport code. The simple fix is to have binding to a transport also hold a reference to the transport's module, removing this class of races. We already had an unused t_owner field which was set for the modular transports and which wasn't set for the built-in loop transport. Signed-off-by: Zach Brown <zach.brown@oracle.com>
* | RDS: remove old rs_transport commentZach Brown2010-09-08
| | | | | | | | | | | | | | rs_transport is now also used by the rdma paths once the socket is bound. We don't need this stale comment to tell us what cscope can. Signed-off-by: Zach Brown <zach.brown@oracle.com>
* | RDS: lock rds_conn_count decrement in rds_conn_destroy()Zach Brown2010-09-08
| | | | | | | | | | | | | | rds_conn_destroy() can race with all other modifications of the rds_conn_count but it was modifying the count without locking. Signed-off-by: Zach Brown <zach.brown@oracle.com>
* | RDS/IB: protect the list of IB devicesZach Brown2010-09-08
| | | | | | | | | | | | | | | | | | | | | | | | | | | | The RDS IB device list wasn't protected by any locking. Traversal in both the get_mr and FMR flushing paths could race with additon and removal. List manipulation is done with RCU primatives and is protected by the write side of a rwsem. The list traversal in the get_mr fast path is protected by a rcu read critical section. The FMR list traversal is more problematic because it can block while traversing the list. We protect this with the read side of the rwsem. Signed-off-by: Zach Brown <zach.brown@oracle.com>
* | RDS/IB: print IB event strings as well as their numberZach Brown2010-09-08
| | | | | | | | | | | | | | | | | | It's nice to not have to go digging in the code to see which event occurred. It's easy to throw together a quick array that maps the ib event enums to their strings. I didn't see anything in the stack that does this translation for us, but I also didn't look very hard. Signed-off-by: Zach Brown <zach.brown@oracle.com>
* | RDS: flush fmrs before allocating new onesChris Mason2010-09-08
| | | | | | | | | | | | | | | | | | | | | | Flushing FMRs is somewhat expensive, and is currently kicked off when the interrupt handler notices that we are getting low. The result of this is that FMR flushing only happens from the interrupt cpus. This spreads the load more effectively by triggering flushes just before we allocate a new FMR. Signed-off-by: Chris Mason <chris.mason@oracle.com>
* | RDS: properly use sg_init_tableChris Mason2010-09-08
| | | | | | | | | | | | This is only needed to keep debugging code from bugging. Signed-off-by: Chris Mason <chris.mason@oracle.com>
* | RDS/IB: track signaled sendsZach Brown2010-09-08
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | We're seeing bugs today where IB connection shutdown clears the send ring while the tasklet is processing completed sends. Implementation details cause this to dereference a null pointer. Shutdown needs to wait for send completion to stop before tearing down the connection. We can't simply wait for the ring to empty because it may contain unsignaled sends that will never be processed. This patch tracks the number of signaled sends that we've posted and waits for them to complete. It also makes sure that the tasklet has finished executing. Signed-off-by: Zach Brown <zach.brown@oracle.com>
* | RDS: remove __init and __exit annotationZach Brown2010-09-08
| | | | | | | | | | | | | | The trivial amount of memory saved isn't worth the cost of dealing with section mismatches. Signed-off-by: Zach Brown <zach.brown@oracle.com>
* | RDS/IB: Use SLAB_HWCACHE_ALIGN flag for kmem_cache_create()Andy Grover2010-09-08
| | | | | | | | | | | | | | We are *definitely* counting cycles as closely as DaveM, so ensure hwcache alignment for our recv ring control structs. Signed-off-by: Andy Grover <andy.grover@oracle.com>
* | RDS/IB: always process recv completionsZach Brown2010-09-08
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | The recv refill path was leaking fragments because the recv event handler had marked a ring element as free without freeing its frag. This was happening because it wasn't processing receives when the conn wasn't marked up or connecting, as can be the case if it races with rmmod. Two observations support always processing receives in the callback. First, buildup should only post receives, thus triggering recv event handler calls, once it has built up all the state to handle them. Teardown should destroy the CQ and drain the ring before tearing down the state needed to process recvs. Both appear to be true today. Second, this test was fundamentally racy. There is nothing to stop rmmod and connection destruction from swooping in the moment after the conn state was sampled but before real receive procesing starts. Signed-off-by: Zach Brown <zach.brown@oracle.com>
* | RDS: return to a single-threaded krdsdZach Brown2010-09-08
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | We were seeing very nasty bugs due to fundamental assumption the current code makes about concurrent work struct processing. The code simpy isn't able to handle concurrent connection shutdown work function execution today, for example, which is very much possible once a multi-threaded krdsd was introduced. The problem compounds as additional work structs are added to the mix. krdsd is no longer perforance critical now that send and receive posting and FMR flushing are done elsewhere, so the safest fix is to move back to the single threaded krdsd that the current code was built around. Signed-off-by: Zach Brown <zach.brown@oracle.com>
* | RDS/IB: create a work queue for FMR flushingZach Brown2010-09-08
| | | | | | | | | | | | | | | | | | | | | | | | This patch moves the FMR flushing work in to its own mult-threaded work queue. This is to maintain performance in preparation for returning the main krdsd work queue back to a single threaded work queue to avoid deep-rooted concurrency bugs. This is also good because it further separates FMRs, which might be removed some day, from the rest of the code base. Signed-off-by: Zach Brown <zach.brown@oracle.com>
* | RDS/IB: destroy connections on rmmodZach Brown2010-09-08
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | IB connections were not being destroyed during rmmod. First, recently IB device removal callback was changed to disconnect connections that used the removing device rather than destroying them. So connections with devices during rmmod were not being destroyed. Second, rds_ib_destroy_nodev_conns() was being called before connections are disassociated with devices. It would almost never find connections in the nodev list. We first get rid of rds_ib_destroy_conns(), which is no longer called, and refactor the existing caller into the main body of the function and get rid of the list and lock wrappers. Then we call rds_ib_destroy_nodev_conns() *after* ib_unregister_client() has removed the IB device from all the conns and put the conns on the nodev list. The result is that IB connections are destroyed by rmmod. Signed-off-by: Zach Brown <zach.brown@oracle.com>
* | RDS/IB: wait for IB dev freeing work to finish during rmmodZach Brown2010-09-08
| | | | | | | | | | | | | | | | The RDS IB client removal callback can queue work to drop the final reference to an IB device. We have to make sure that this function has returned before we complete rmmod or the work threads can try to execute freed code. Signed-off-by: Zach Brown <zach.brown@oracle.com>
* | RDS/IB: Make ib_recv_refill return voidAndy Grover2010-09-08
| | | | | | | | Signed-off-by: Andy Grover <andy.grover@oracle.com>
* | RDS: Remove unused XLIST_PTR_TAIL and xlist_protect()Andy Grover2010-09-08
| | | | | | | | | | | | Not used. Signed-off-by: Andy Grover <andy.grover@oracle.com>
* | RDS: whitespaceAndy Grover2010-09-08
| |
* | RDS: use delayed work for the FMR flushesChris Mason2010-09-08
| | | | | | | | | | | | | | | | Using a delayed work queue helps us make sure a healthy number of FMRs have queued up over the limit. It makes for a large improvement in RDMA iops. Signed-off-by: Chris Mason <chris.mason@oracle.com>
* | rds: more FMRs are fasterChris Mason2010-09-08
| | | | | | | | | | | | When we add more FMRs, we flush them less often and so we go faster. Signed-off-by: Chris Mason <chris.mason@oracle.com>
* | rds: recycle FMRs through lockless listsChris Mason2010-09-08
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | FRM allocation and recycling is performance critical and fairly lock intensive. The current code has a per connection lock that all processes bang on and it becomes a major bottleneck on large systems. This changes things to use a number of cmpxchg based lists instead, allowing us to go through the whole FMR lifecycle without locking inside RDS. Zach Brown pointed out that our usage of cmpxchg for xlist removal is racey if someone manages to remove and add back an FMR struct into the list while another CPU can see the FMR's address at the head of the list. The second CPU might assume the list hasn't changed when in fact any number of operations might have happened in between the deletion and reinsertion. This commit maintains a per cpu count of CPUs that are currently in xlist removal, and establishes a grace period to make sure that nobody can see an entry we have just removed from the list. Signed-off-by: Chris Mason <chris.mason@oracle.com>
* | rds: fix rds_send_xmit() serializationZach Brown2010-09-08
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | rds_send_xmit() was changed to hold an interrupt masking spinlock instead of a mutex so that it could be called from the IB receive tasklet path. This broke the TCP transport because its xmit method can block and masks and unmasks interrupts. This patch serializes callers to rds_send_xmit() with a simple bit instead of the current spinlock or previous mutex. This enables rds_send_xmit() to be called from any context and to call functions which block. Getting rid of the c_send_lock exposes the bare c_lock acquisitions which are changed to block interrupts. A waitqueue is added so that rds_conn_shutdown() can wait for callers to leave rds_send_xmit() before tearing down partial send state. This lets us get rid of c_senders. rds_send_xmit() is changed to check the conn state after acquiring the RDS_IN_XMIT bit to resolve races with the shutdown path. Previously both worked with the conn state and then the lock in the same order, allowing them to race and execute the paths concurrently. rds_send_reset() isn't racing with rds_send_xmit() now that rds_conn_shutdown() properly ensures that rds_send_xmit() can't start once the conn state has been changed. We can remove its previous use of the spinlock. Finally, c_send_generation is redundant. Callers can race to test the c_flags bit by simply retrying instead of racing to test the c_send_generation atomic. Signed-off-by: Zach Brown <zach.brown@oracle.com>
* | rds: block ints when acquiring c_lock in rds_conn_message_info()Zach Brown2010-09-08
| | | | | | | | | | | | | | | | conn->c_lock is acquired in interrupt context. rds_conn_message_info() is called from user context and was acquiring c_lock without blocking interrupts, leading to possible deadlocks. Signed-off-by: Zach Brown <zach.brown@oracle.com>
* | rds: remove unused rds_send_acked_before()Zach Brown2010-09-08
| | | | | | | | | | | | | | | | rds_send_acked_before() wasn't blocking interrupts when acquiring c_lock from user context but nothing calls it. Rather than fix its use of c_lock we just remove the function. Signed-off-by: Zach Brown <zach.brown@oracle.com>
* | RDS: use friendly gfp masks for prefillChris Mason2010-09-08
| | | | | | | | | | | | | | | | | | When prefilling the rds frags, we end up doing a lot of allocations. We're not in atomic context here, and so there's no reason to dip into atomic reserves. This changes the prefills to use masks that allow waiting. Signed-off-by: Chris Mason <chris.mason@oracle.com>
* | RDS/IB: Add caching of frags and incsChris Mason2010-09-08
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | This patch is based heavily on an initial patch by Chris Mason. Instead of freeing slab memory and pages, it keeps them, and funnels them back to be reused. The lock minimization strategy uses xchg and cmpxchg atomic ops for manipulation of pointers to list heads. We anchor the lists with a pointer to a list_head struct instead of a static list_head struct. We just have to carefully use the existing primitives with the difference between a pointer and a static head struct. For example, 'list_empty()' means that our anchor pointer points to a list with a single item instead of meaning that our static head element doesn't point to any list items. Original patch by Chris, with significant mods and fixes by Andy and Zach. Signed-off-by: Chris Mason <chris.mason@oracle.com> Signed-off-by: Andy Grover <andy.grover@oracle.com> Signed-off-by: Zach Brown <zach.brown@oracle.com>
* | RDS/IB: Remove ib_recv_unmap_page()Andy Grover2010-09-08
| | | | | | | | | | | | | | | | | | All it does is call unmap_sg(), so just call that directly. The comment above unmap_page also may be incorrect, so we shouldn't hold on to it, either. Signed-off-by: Andy Grover <andy.grover@oracle.com>
* | RDS: Assume recv->r_frag is always NULL in refill_one()Andy Grover2010-09-08
| | | | | | | | | | | | | | | | | | | | | | refill_one() should never be called on a recv struct that doesn't need a new r_frag allocated. Add a WARN and remove conditional around r_frag alloc code. Also, add a comment to explain why r_ibinc may or may not need refilling. Signed-off-by: Andy Grover <andy.grover@oracle.com>
* | RDS: Use page_remainder_alloc() for recv bufsAndy Grover2010-09-08
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Instead of splitting up a page into RDS_FRAG_SIZE chunks ourselves, ask rds_page_remainder_alloc() to do it. While it is possible PAGE_SIZE > FRAG_SIZE, on x86en it isn't, so having duplicate "carve up a page into buffers" code seems excessive. The other modification this spawns is the use of a single struct scatterlist in rds_page_frag instead of a bare page ptr. This causes verbosity to increase in some places, and decrease in others. Finally, I decided to unify the lifetimes and alloc/free of rds_page_frag and its page. This is a nice simplification in itself, but will be extra-nice once we come to adding cmason's recycling patch. Signed-off-by: Andy Grover <andy.grover@oracle.com>
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