On Wed, Oct 30, 2019 at 03:43:10PM +0530, Ritesh Harjani wrote: > > > On 10/30/19 9:56 AM, Gao Xiang wrote: > > Similar to [1] [2], it seems a trivial cleanup since > > bio_alloc can handle memory allocation as mentioned in > > fs/direct-io.c (also see fs/block_dev.c, fs/buffer.c, ..) > > > > AFAIU, the reason is that, bio_alloc with __GFP_DIRECT_RECLAIM > flags guarantees bio allocation under some given restrictions, > as stated in fs/direct-io.c > So here it is ok to not check for NULL value from bio_alloc. > > I think we can update above info too in your commit msg. Please also add a short comment in the code itself, so it's clear why it's OK to skip the error check, and reference the comments for bio_alloc_bioset(). This is the fairly subtle bit which makes this change not obvious: * When @bs is not NULL, if %__GFP_DIRECT_RECLAIM is set then bio_alloc will * always be able to allocate a bio. This is due to the mempool guarantees. * To make this work, callers must never allocate more than 1 bio at a time * from this pool. Callers that need to allocate more than 1 bio must always * submit the previously allocated bio for IO before attempting to allocate * a new one. Failure to do so can cause deadlocks under memory pressure. * * Note that when running under generic_make_request() (i.e. any block * driver), bios are not submitted until after you return - see the code in * generic_make_request() that converts recursion into iteration, to prevent * stack overflows. * * This would normally mean allocating multiple bios under * generic_make_request() would be susceptible to deadlocks, but we have * deadlock avoidance code that resubmits any blocked bios from a rescuer * thread. Otherwise, someone else may not understand why it's safe to not check the error return then submit cleanup patch to add the error checking back. :-) - Ted
