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Clarified a source code comment.

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git-svn-id: http://svn.code.sf.net/p/scst/svn/trunk@1543 d57e44dd-8a1f-0410-8b47-8ef2f437770f
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Bart Van Assche
2010-03-15 19:25:29 +00:00
parent ab5da422b8
commit b05d967c8a
1 changed files with 15 additions and 8 deletions
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srpt/src/ib_srpt.c
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@@ -2558,14 +2558,21 @@ out:
* srpt_must_wait_for_cred() - Whether or not the target must wait with
* sending a response towards the initiator in order to avoid that the
* initiator locks up. The Linux SRP initiator locks up when:
* initiator.req_lim < req_lim_min (2 for SRP_CMD; 1 for SRP_TSK_MGMT).
* no new SRP_RSP is received, or new SRP_RSP do not increase initiator.req_lim.
* In order to avoid an initiator lock up, the target must not send an SRP_RSP
* that keeps initiator.req_lim < req_lim_min when initiator.req_lim
* < req_lim_min. when target.req_lim == req_lim_min - 1, initiator.req_lim must
* also equal req_lim_min - 1 because of the credit mechanism defined in the
* SRP standard. Hence wait with sending a response if that response would not
* increase initiator.req_lim.
* initiator.req_lim < req_lim_min (req_lim_min equals 2 for SRP_CMD and
* equals 1 for SRP_TSK_MGMT), no new SRP_RSP will be received by the
* initiator, or none of the received SRP_RSP responses increases
* initiator.req_lim. One possible strategy to avoid an initiator lockup is
* that the target does not send an SRP_RSP that makes initiator.req_lim <
* req_lim_min. While the target does not know the value of initiator.req_lim,
* one can deduce from the credit mechanism specified in the SRP standard that
* when target.req_lim == req_lim_min - 1, initiator.req_lim must also equal
* req_lim_min - 1. Hence wait with sending a response when target.req_lim <
* req_lim_min if that response would not increase initiator.req_lim. The last
* condition is equivalent to srpt_req_lim_delta(ch) + 1 <= 0, which is also
* equivalent to ch->req_lim - ch->last_response_req_lim + 1 <= 0.
*
* See also: For more information about how to reproduce the initiator lockup,
* see also http://bugzilla.kernel.org/show_bug.cgi?id=14235.
*/
static bool srpt_must_wait_for_cred(struct srpt_rdma_ch *ch, int req_lim_min)
{