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When the kernel was compiled using the UBSAN option,
we saw the following stack trace:
[ 1184.827917] UBSAN: Undefined behaviour in drivers/infiniband/hw/mlx4/mr.c:349:27
[ 1184.828114] signed integer overflow:
[ 1184.828247] -2147483648 - 1 cannot be represented in type 'int'
The problem was caused by calling round_up in procedure
mlx4_ib_umem_calc_optimal_mtt_size (on line 349, as noted in the stack
trace) with the second parameter (1 << block_shift) (which is an int).
The second parameter should have been (1ULL << block_shift) (which
is an unsigned long long).
(1 << block_shift) is treated by the compiler as an int (because 1 is
an integer).
Now, local variable block_shift is initialized to 31.
If block_shift is 31, 1 << block_shift is 1 << 31 = 0x80000000=-214748368.
This is the most negative int value.
Inside the round_up macro, there is a cast applied to ((1 << 31) - 1).
However, this cast is applied AFTER ((1 << 31) - 1) is calculated.
Since (1 << 31) is treated as an int, we get the negative overflow
identified by UBSAN in the process of calculating ((1 << 31) - 1).
The fix is to change (1 << block_shift) to (1ULL << block_shift) on
line 349.
Fixes: 9901abf583 ("IB/mlx4: Use optimal numbers of MTT entries")
Signed-off-by: Jack Morgenstein <jackm@dev.mellanox.co.il>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>
Linux kernel
============
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In order to build the documentation, use ``make htmldocs`` or
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There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.
Please read the Documentation/process/changes.rst file, as it contains the
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the problems which may result by upgrading your kernel.